diff --git a/src/cli/aws/__tests__/transaction-search.test.ts b/src/cli/aws/__tests__/transaction-search.test.ts
index 67ccd0ac6..33965d071 100644
--- a/src/cli/aws/__tests__/transaction-search.test.ts
+++ b/src/cli/aws/__tests__/transaction-search.test.ts
@@ -163,7 +163,8 @@ describe('enableTransactionSearch', () => {
       const result = await enableTransactionSearch('us-east-1', '123456789012');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Insufficient permissions to enable Application Signals');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Insufficient permissions to enable Application Signals');
     });
 
     it('returns error when Application Signals fails with generic error', async () => {
@@ -172,7 +173,8 @@ describe('enableTransactionSearch', () => {
       const result = await enableTransactionSearch('us-east-1', '123456789012');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Failed to enable Application Signals');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Failed to enable Application Signals');
     });
 
     it('returns error when CloudWatch Logs policy fails with AccessDenied', async () => {
@@ -184,7 +186,8 @@ describe('enableTransactionSearch', () => {
       const result = await enableTransactionSearch('us-east-1', '123456789012');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Insufficient permissions to configure CloudWatch Logs policy');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Insufficient permissions to configure CloudWatch Logs policy');
     });
 
     it('returns error when trace destination fails', async () => {
@@ -195,7 +198,8 @@ describe('enableTransactionSearch', () => {
       const result = await enableTransactionSearch('us-east-1', '123456789012');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Failed to configure trace destination');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Failed to configure trace destination');
     });
 
     it('returns error when indexing rule update fails', async () => {
@@ -215,7 +219,8 @@ describe('enableTransactionSearch', () => {
       const result = await enableTransactionSearch('us-east-1', '123456789012');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Failed to configure indexing rules');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Failed to configure indexing rules');
     });
 
     it('does not proceed to later steps when an earlier step fails', async () => {
diff --git a/src/cli/aws/transaction-search.ts b/src/cli/aws/transaction-search.ts
index 3a3b53fa6..e60e67206 100644
--- a/src/cli/aws/transaction-search.ts
+++ b/src/cli/aws/transaction-search.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../lib/types';
 import { getErrorMessage, isAccessDeniedError } from '../errors';
 import { getCredentialProvider } from './account';
 import { arnPrefix } from './partition';
@@ -14,10 +15,7 @@ import {
   XRayClient,
 } from '@aws-sdk/client-xray';
 
-export interface TransactionSearchEnableResult {
-  success: boolean;
-  error?: string;
-}
+export type TransactionSearchEnableResult = Result;
 
 const RESOURCE_POLICY_NAME = 'TransactionSearchXRayAccess';
 
@@ -44,9 +42,9 @@ export async function enableTransactionSearch(
   } catch (err: unknown) {
     const message = getErrorMessage(err);
     if (isAccessDeniedError(err)) {
-      return { success: false, error: `Insufficient permissions to enable Application Signals: ${message}` };
+      return { success: false, error: new Error(`Insufficient permissions to enable Application Signals: ${message}`) };
     }
-    return { success: false, error: `Failed to enable Application Signals: ${message}` };
+    return { success: false, error: new Error(`Failed to enable Application Signals: ${message}`) };
   }
 
   // Step 2: Create CloudWatch Logs resource policy for X-Ray (if needed)
@@ -80,9 +78,12 @@ export async function enableTransactionSearch(
   } catch (err: unknown) {
     const message = getErrorMessage(err);
     if (isAccessDeniedError(err)) {
-      return { success: false, error: `Insufficient permissions to configure CloudWatch Logs policy: ${message}` };
+      return {
+        success: false,
+        error: new Error(`Insufficient permissions to configure CloudWatch Logs policy: ${message}`),
+      };
     }
-    return { success: false, error: `Failed to configure CloudWatch Logs policy: ${message}` };
+    return { success: false, error: new Error(`Failed to configure CloudWatch Logs policy: ${message}`) };
   }
 
   const xrayClient = new XRayClient({ region, credentials });
@@ -96,9 +97,12 @@ export async function enableTransactionSearch(
   } catch (err: unknown) {
     const message = getErrorMessage(err);
     if (isAccessDeniedError(err)) {
-      return { success: false, error: `Insufficient permissions to configure trace destination: ${message}` };
+      return {
+        success: false,
+        error: new Error(`Insufficient permissions to configure trace destination: ${message}`),
+      };
     }
-    return { success: false, error: `Failed to configure trace destination: ${message}` };
+    return { success: false, error: new Error(`Failed to configure trace destination: ${message}`) };
   }
 
   // Step 4: Set indexing to 100% on the built-in Default rule (always exists, idempotent)
@@ -112,9 +116,9 @@ export async function enableTransactionSearch(
   } catch (err: unknown) {
     const message = getErrorMessage(err);
     if (isAccessDeniedError(err)) {
-      return { success: false, error: `Insufficient permissions to configure indexing rules: ${message}` };
+      return { success: false, error: new Error(`Insufficient permissions to configure indexing rules: ${message}`) };
     }
-    return { success: false, error: `Failed to configure indexing rules: ${message}` };
+    return { success: false, error: new Error(`Failed to configure indexing rules: ${message}`) };
   }
 
   return { success: true };
diff --git a/src/cli/commands/add/types.ts b/src/cli/commands/add/types.ts
index a066b1cc3..089abcfe1 100644
--- a/src/cli/commands/add/types.ts
+++ b/src/cli/commands/add/types.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import type {
   GatewayAuthorizerType,
   ModelProvider,
@@ -41,12 +42,7 @@ export interface AddAgentOptions extends VpcOptions {
   json?: boolean;
 }
 
-export interface AddAgentResult {
-  success: boolean;
-  agentName?: string;
-  agentPath?: string;
-  error?: string;
-}
+export type AddAgentResult = Result<{ agentName?: string; agentPath?: string }>;
 
 // Gateway types
 export interface AddGatewayOptions {
@@ -68,11 +64,7 @@ export interface AddGatewayOptions {
   json?: boolean;
 }
 
-export interface AddGatewayResult {
-  success: boolean;
-  gatewayName?: string;
-  error?: string;
-}
+export type AddGatewayResult = Result<{ gatewayName?: string }>;
 
 // Gateway Target types
 export interface AddGatewayTargetOptions {
@@ -100,12 +92,7 @@ export interface AddGatewayTargetOptions {
   json?: boolean;
 }
 
-export interface AddGatewayTargetResult {
-  success: boolean;
-  toolName?: string;
-  sourcePath?: string;
-  error?: string;
-}
+export type AddGatewayTargetResult = Result<{ toolName?: string; sourcePath?: string }>;
 
 // Memory types (v2: no owner/user concept)
 export interface AddMemoryOptions {
@@ -119,11 +106,7 @@ export interface AddMemoryOptions {
   json?: boolean;
 }
 
-export interface AddMemoryResult {
-  success: boolean;
-  memoryName?: string;
-  error?: string;
-}
+export type AddMemoryResult = Result<{ memoryName?: string }>;
 
 // Credential types (v2: credential, no owner/user concept)
 export interface AddCredentialOptions {
@@ -140,8 +123,4 @@ export interface AddCredentialOptions {
 /** @deprecated Use AddCredentialOptions */
 export type AddIdentityOptions = AddCredentialOptions;
 
-export interface AddCredentialResult {
-  success: boolean;
-  credentialName?: string;
-  error?: string;
-}
+export type AddCredentialResult = Result<{ credentialName?: string }>;
diff --git a/src/cli/commands/create/action.ts b/src/cli/commands/create/action.ts
index a00397f38..02bb1dd2e 100644
--- a/src/cli/commands/create/action.ts
+++ b/src/cli/commands/create/action.ts
@@ -57,7 +57,7 @@ export async function createProject(options: CreateProjectOptions): Promise<Crea
 
     // Fail on errors
     if (!depCheck.passed) {
-      return { success: false, error: depCheck.errors.join('\n'), warnings: depWarnings };
+      return { success: false, error: new Error(depCheck.errors.join('\n')), warnings: depWarnings };
     }
   }
 
@@ -93,7 +93,7 @@ export async function createProject(options: CreateProjectOptions): Promise<Crea
       const gitResult = await initGitRepo(projectRoot);
       if (gitResult.status === 'error') {
         onProgress?.('Initialize git repository', 'error');
-        return { success: false, error: gitResult.message, warnings: depWarnings };
+        return { success: false, error: new Error(gitResult.message), warnings: depWarnings };
       }
       onProgress?.('Initialize git repository', 'done');
     }
@@ -104,7 +104,7 @@ export async function createProject(options: CreateProjectOptions): Promise<Crea
       warnings: depWarnings.length > 0 ? depWarnings : undefined,
     };
   } catch (err) {
-    return { success: false, error: getErrorMessage(err), warnings: depWarnings };
+    return { success: false, error: new Error(getErrorMessage(err)), warnings: depWarnings };
   }
 }
 
@@ -174,7 +174,7 @@ export async function createProjectWithAgent(options: CreateWithAgentOptions): P
 
   // Fail on errors
   if (!depCheck.passed) {
-    return { success: false, error: depCheck.errors.join('\n'), warnings: depWarnings };
+    return { success: false, error: new Error(depCheck.errors.join('\n')), warnings: depWarnings };
   }
 
   // First create the base project (skip dependency check since we already did it)
@@ -217,7 +217,7 @@ export async function createProjectWithAgent(options: CreateWithAgentOptions): P
         warnings: depWarnings.length > 0 ? depWarnings : undefined,
       };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err), warnings: depWarnings };
+      return { success: false, error: new Error(getErrorMessage(err)), warnings: depWarnings };
     }
   }
 
@@ -310,7 +310,7 @@ export async function createProjectWithAgent(options: CreateWithAgentOptions): P
       warnings: depWarnings.length > 0 ? depWarnings : undefined,
     };
   } catch (err) {
-    return { success: false, error: getErrorMessage(err), warnings: depWarnings };
+    return { success: false, error: new Error(getErrorMessage(err)), warnings: depWarnings };
   }
 }
 
diff --git a/src/cli/commands/create/command.tsx b/src/cli/commands/create/command.tsx
index 42c8c7403..7b5cddc89 100644
--- a/src/cli/commands/create/command.tsx
+++ b/src/cli/commands/create/command.tsx
@@ -94,7 +94,7 @@ async function handleCreateCLI(options: CreateOptions): Promise<void> {
     const result = getDryRunInfo({ name: name!, projectName, cwd, language: options.language });
     if (options.json) {
       console.log(JSON.stringify(result));
-    } else {
+    } else if (result.success) {
       console.log('Dry run - would create:');
       for (const path of result.wouldCreate ?? []) {
         console.log(`  ${path}`);
@@ -158,7 +158,7 @@ async function handleCreateCLI(options: CreateOptions): Promise<void> {
       });
 
   if (options.json) {
-    console.log(JSON.stringify(result));
+    console.log(JSON.stringify(result.success ? result : { ...result, error: result.error.message }));
   } else if (result.success) {
     printCreateSummary(projectName!, result.agentName, options.language, options.framework);
     if (options.skipInstall) {
@@ -167,7 +167,7 @@ async function handleCreateCLI(options: CreateOptions): Promise<void> {
       );
     }
   } else {
-    console.error(result.error);
+    console.error(result.error.message);
   }
 
   process.exit(result.success ? 0 : 1);
diff --git a/src/cli/commands/create/types.ts b/src/cli/commands/create/types.ts
index f762a36eb..4216edf83 100644
--- a/src/cli/commands/create/types.ts
+++ b/src/cli/commands/create/types.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import type { VpcOptions } from '../shared/vpc-utils';
 
 export interface CreateOptions extends VpcOptions {
@@ -28,12 +29,10 @@ export interface CreateOptions extends VpcOptions {
   json?: boolean;
 }
 
-export interface CreateResult {
-  success: boolean;
+export type CreateResult = Result<{
   projectPath?: string;
   agentName?: string;
-  error?: string;
   dryRun?: boolean;
   wouldCreate?: string[];
   warnings?: string[];
-}
+}> & { warnings?: string[] };
diff --git a/src/cli/commands/deploy/actions.ts b/src/cli/commands/deploy/actions.ts
index acae6fb03..5573bc0a6 100644
--- a/src/cli/commands/deploy/actions.ts
+++ b/src/cli/commands/deploy/actions.ts
@@ -85,7 +85,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
       logger.finalize(false);
       return {
         success: false,
-        error: `Target "${options.target}" not found in aws-targets.json`,
+        error: new Error(`Target "${options.target}" not found in aws-targets.json`),
         logPath: logger.getRelativeLogPath(),
       };
     }
@@ -114,8 +114,9 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
       logger.finalize(false);
       return {
         success: false,
-        error:
-          'This will delete all deployed resources and the CloudFormation stack. Run with --yes to confirm teardown.',
+        error: new Error(
+          'This will delete all deployed resources and the CloudFormation stack. Run with --yes to confirm teardown.'
+        ),
         logPath: logger.getRelativeLogPath(),
       };
     }
@@ -169,7 +170,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
           errorResult?.error && typeof errorResult.error === 'string' ? errorResult.error : 'Identity setup failed';
         endStep('error', errorMsg);
         logger.finalize(false);
-        return { success: false, error: errorMsg, logPath: logger.getRelativeLogPath() };
+        return { success: false, error: new Error(errorMsg), logPath: logger.getRelativeLogPath() };
       }
       identityKmsKeyArn = identityResult.kmsKeyArn;
 
@@ -201,7 +202,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
         const errorMsg = 'OAuth credential setup failed. Check the log for details.';
         endStep('error', errorMsg);
         logger.finalize(false);
-        return { success: false, error: errorMsg, logPath: logger.getRelativeLogPath() };
+        return { success: false, error: new Error(errorMsg), logPath: logger.getRelativeLogPath() };
       }
 
       // Collect OAuth credential ARNs for deployed state
@@ -242,7 +243,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
     if (stackNames.length === 0) {
       endStep('error', 'No stacks found');
       logger.finalize(false);
-      return { success: false, error: 'No stacks found to deploy', logPath: logger.getRelativeLogPath() };
+      return { success: false, error: new Error('No stacks found to deploy'), logPath: logger.getRelativeLogPath() };
     }
     const stackName = stackNames[0]!;
     endStep('success');
@@ -259,7 +260,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
         logger.finalize(false);
         return {
           success: false,
-          error: 'AWS environment needs bootstrapping. Run with --yes to auto-bootstrap.',
+          error: new Error('AWS environment needs bootstrapping. Run with --yes to auto-bootstrap.'),
           logPath: logger.getRelativeLogPath(),
         };
       }
@@ -274,7 +275,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
       logger.finalize(false);
       return {
         success: false,
-        error: deployabilityCheck.message ?? 'Stack is not in a deployable state',
+        error: new Error(deployabilityCheck.message ?? 'Stack is not in a deployable state'),
         logPath: logger.getRelativeLogPath(),
       };
     }
@@ -359,7 +360,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
         logger.finalize(false);
         return {
           success: false,
-          error: `Stack teardown failed: ${teardownError}`,
+          error: new Error(`Stack teardown failed: ${teardownError}`),
           logPath: logger.getRelativeLogPath(),
         };
       }
@@ -639,8 +640,8 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
           agentNames,
           hasGateways,
         });
-        if (tsResult.error) {
-          logger.log(`Transaction search setup warning: ${tsResult.error}`, 'warn');
+        if (!tsResult.success) {
+          logger.log(`Transaction search setup warning: ${tsResult.error.message}`, 'warn');
         } else {
           notes.push(
             'Transaction search enabled. It takes ~10 minutes for transaction search to be fully active and for traces from invocations to be indexed.'
@@ -666,7 +667,7 @@ export async function handleDeploy(options: ValidatedDeployOptions): Promise<Dep
   } catch (err: unknown) {
     logger.log(getErrorMessage(err), 'error');
     logger.finalize(false);
-    return { success: false, error: getErrorMessage(err), logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(getErrorMessage(err)), logPath: logger.getRelativeLogPath() };
   } finally {
     if (toolkitWrapper) {
       await toolkitWrapper.dispose();
diff --git a/src/cli/commands/deploy/command.tsx b/src/cli/commands/deploy/command.tsx
index 5bc6e96d1..b6a76ff9f 100644
--- a/src/cli/commands/deploy/command.tsx
+++ b/src/cli/commands/deploy/command.tsx
@@ -85,7 +85,7 @@ async function handleDeployCLI(options: DeployOptions): Promise<void> {
   }
 
   if (options.json) {
-    console.log(JSON.stringify(result));
+    console.log(JSON.stringify(result.success ? result : { ...result, error: result.error.message }));
   } else if (result.success) {
     if (options.diff) {
       console.log(`\n✓ Diff complete for '${result.targetName}' (stack: ${result.stackName})`);
@@ -125,7 +125,7 @@ async function handleDeployCLI(options: DeployOptions): Promise<void> {
       console.log(`\nLog: ${result.logPath}`);
     }
   } else {
-    console.error(result.error);
+    console.error(result.error.message);
     if (result.logPath) {
       console.error(`Log: ${result.logPath}`);
     }
diff --git a/src/cli/commands/deploy/types.ts b/src/cli/commands/deploy/types.ts
index 44cdc7847..e005840ee 100644
--- a/src/cli/commands/deploy/types.ts
+++ b/src/cli/commands/deploy/types.ts
@@ -1,3 +1,5 @@
+import type { Result } from '../../../lib/types';
+
 export interface DeployOptions {
   target?: string;
   yes?: boolean;
@@ -8,8 +10,7 @@ export interface DeployOptions {
   diff?: boolean;
 }
 
-export interface DeployResult {
-  success: boolean;
+export type DeployResult = Result<{
   targetName?: string;
   stackName?: string;
   outputs?: Record<string, string>;
@@ -17,12 +18,6 @@ export interface DeployResult {
   nextSteps?: string[];
   notes?: string[];
   postDeployWarnings?: string[];
-  error?: string;
-}
+}> & { logPath?: string };
 
-export interface PreflightResult {
-  success: boolean;
-  stackNames?: string[];
-  needsBootstrap?: boolean;
-  error?: string;
-}
+export type PreflightResult = Result;
diff --git a/src/cli/commands/dev/browser-mode.ts b/src/cli/commands/dev/browser-mode.ts
index c35113e6d..9cfcc331b 100644
--- a/src/cli/commands/dev/browser-mode.ts
+++ b/src/cli/commands/dev/browser-mode.ts
@@ -199,7 +199,7 @@ export async function runBrowserMode(opts: BrowserModeOptions): Promise<void> {
           const configIO = new ConfigIO({ baseDir });
           const context = await loadDeployedProjectConfig(configIO);
           const resolved = resolveAgent(context, { runtime: agentName });
-          if (!resolved.success) return { success: false, error: resolved.error };
+          if (!resolved.success) return { success: false, error: resolved.error.message };
           return listTraces({
             region: resolved.agent.region,
             runtimeId: resolved.agent.runtimeId,
@@ -219,7 +219,7 @@ export async function runBrowserMode(opts: BrowserModeOptions): Promise<void> {
           const configIO = new ConfigIO({ baseDir });
           const context = await loadDeployedProjectConfig(configIO);
           const resolved = resolveAgent(context, { runtime: agentName });
-          if (!resolved.success) return { success: false, error: resolved.error };
+          if (!resolved.success) return { success: false, error: resolved.error.message };
           return fetchTraceRecords({
             region: resolved.agent.region,
             runtimeId: resolved.agent.runtimeId,
diff --git a/src/cli/commands/eval/command.tsx b/src/cli/commands/eval/command.tsx
index 9dff195c4..3431138cd 100644
--- a/src/cli/commands/eval/command.tsx
+++ b/src/cli/commands/eval/command.tsx
@@ -33,7 +33,7 @@ export const registerEval = (program: Command) => {
         }
 
         if (!result.success) {
-          render(<Text color="red">{result.error}</Text>);
+          render(<Text color="red">{result.error.message}</Text>);
           process.exit(1);
         }
 
diff --git a/src/cli/commands/import/__tests__/idempotency.test.ts b/src/cli/commands/import/__tests__/idempotency.test.ts
index 4b1938e28..9b236db44 100644
--- a/src/cli/commands/import/__tests__/idempotency.test.ts
+++ b/src/cli/commands/import/__tests__/idempotency.test.ts
@@ -280,8 +280,8 @@ describe('Import Idempotency (Test Group 7)', () => {
       const result = await handleImport({ source: '/tmp/config.yaml' });
 
       expect(result.success).toBe(true);
-      expect(result.importedAgents).toContain('my-agent');
-      expect(result.importedMemories).toContain('my-memory');
+      expect(result.success ? result.importedAgents : undefined).toContain('my-agent');
+      expect(result.success ? result.importedMemories : undefined).toContain('my-memory');
 
       expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(1);
       const writtenSpec = mockConfigIOInstance.writeProjectSpec.mock.calls[0]![0];
@@ -394,8 +394,8 @@ describe('Import Idempotency (Test Group 7)', () => {
       const result = await handleImport({ source: '/tmp/config.yaml' });
 
       expect(result.success).toBe(true);
-      expect(result.importedAgents).toEqual([]);
-      expect(result.importedMemories).toEqual([]);
+      expect(result.success ? result.importedAgents : undefined).toEqual([]);
+      expect(result.success ? result.importedMemories : undefined).toEqual([]);
     });
 
     it('does not corrupt deployed state on second import', async () => {
@@ -611,7 +611,7 @@ describe('Import Idempotency (Test Group 7)', () => {
       const result = await handleImport({ source: '/tmp/config.yaml' });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('No agents found');
+      expect(!result.success ? result.error.message : undefined).toContain('No agents found');
     });
 
     it('returns error when no project found', async () => {
@@ -620,7 +620,7 @@ describe('Import Idempotency (Test Group 7)', () => {
       const result = await handleImport({ source: '/tmp/config.yaml' });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('No agentcore project found');
+      expect(!result.success ? result.error.message : undefined).toContain('No agentcore project found');
     });
   });
 
diff --git a/src/cli/commands/import/__tests__/import-gateway-flow.test.ts b/src/cli/commands/import/__tests__/import-gateway-flow.test.ts
index 183a6e63f..0c44dc87b 100644
--- a/src/cli/commands/import/__tests__/import-gateway-flow.test.ts
+++ b/src/cli/commands/import/__tests__/import-gateway-flow.test.ts
@@ -178,7 +178,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(true);
-      expect(result.resourceId).toBe(GATEWAY_ID);
+      expect(result.success ? result.resourceId : undefined).toBe(GATEWAY_ID);
       expect(result.resourceType).toBe('gateway');
       expect(result.resourceName).toBe(GATEWAY_NAME);
 
@@ -195,12 +195,12 @@ describe('handleImportGateway', () => {
 
   describe('Rollback', () => {
     it('rolls back config on pipeline failure', async () => {
-      mockExecuteCdkImportPipeline.mockResolvedValue({ success: false, error: 'Phase 2 failed' });
+      mockExecuteCdkImportPipeline.mockResolvedValue({ success: false, error: new Error('Phase 2 failed') });
 
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(false);
-      expect(result.error).toBe('Phase 2 failed');
+      expect(!result.success ? result.error.message : undefined).toBe('Phase 2 failed');
 
       // First call = write merged config, second call = rollback
       expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
@@ -214,7 +214,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Could not find logical ID');
+      expect(!result.success ? result.error.message : undefined).toContain('Could not find logical ID');
 
       // First call = write merged config, second call = rollback
       expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
@@ -232,7 +232,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('already exists');
+      expect(!result.success ? result.error.message : undefined).toContain('already exists');
       expect(mockConfigIOInstance.writeProjectSpec).not.toHaveBeenCalled();
     });
 
@@ -303,7 +303,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('already exists');
+      expect(!result.success ? result.error.message : undefined).toContain('already exists');
     });
   });
 
@@ -316,7 +316,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({ arn: GATEWAY_ARN });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Invalid name');
+      expect(!result.success ? result.error.message : undefined).toContain('Invalid name');
       expect(mockConfigIOInstance.writeProjectSpec).not.toHaveBeenCalled();
     });
 
@@ -344,7 +344,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({});
 
       expect(result.success).toBe(true);
-      expect(result.resourceId).toBe(GATEWAY_ID);
+      expect(result.success ? result.resourceId : undefined).toBe(GATEWAY_ID);
       expect(mockGetGatewayDetail).toHaveBeenCalledWith({ region: REGION, gatewayId: GATEWAY_ID });
     });
 
@@ -357,7 +357,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({});
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Multiple gateways found');
+      expect(!result.success ? result.error.message : undefined).toContain('Multiple gateways found');
     });
 
     it('fails when no gateways exist and no --arn', async () => {
@@ -366,7 +366,7 @@ describe('handleImportGateway', () => {
       const result = await handleImportGateway({});
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('No gateways found');
+      expect(!result.success ? result.error.message : undefined).toContain('No gateways found');
     });
   });
 
diff --git a/src/cli/commands/import/__tests__/import-no-deploy.test.ts b/src/cli/commands/import/__tests__/import-no-deploy.test.ts
index f0b84303f..a29dff3bd 100644
--- a/src/cli/commands/import/__tests__/import-no-deploy.test.ts
+++ b/src/cli/commands/import/__tests__/import-no-deploy.test.ts
@@ -489,10 +489,10 @@ agents:
     });
 
     expect(result.success).toBe(true);
-    expect(result.importedAgents).toEqual([]);
-    expect(result.importedMemories).toEqual([]);
-    expect(result.stackName).toBeDefined();
-    expect(result.projectSpec).toBeDefined();
+    expect(result.success ? result.importedAgents : undefined).toEqual([]);
+    expect(result.success ? result.importedMemories : undefined).toEqual([]);
+    expect(result.success ? result.stackName : undefined).toBeDefined();
+    expect(result.success ? result.projectSpec : undefined).toBeDefined();
   });
 
   it('emits "No deployed resources found" message', async () => {
@@ -645,7 +645,7 @@ agents:
     const { handleImport } = await import('../actions.js');
     const result = await handleImport({ source: yamlPath });
 
-    expect(result.stackName).toBe('AgentCore-myproject-default');
+    expect(result.success ? result.stackName : undefined).toBe('AgentCore-myproject-default');
   });
 });
 
@@ -725,8 +725,8 @@ agents:
     // No physical IDs means target resolution is skipped entirely.
     // The import succeeds -- config merge + source copy still happen.
     expect(result.success).toBe(true);
-    expect(result.importedAgents).toEqual([]);
-    expect(result.importedMemories).toEqual([]);
+    expect(result.success ? result.importedAgents : undefined).toEqual([]);
+    expect(result.success ? result.importedMemories : undefined).toEqual([]);
   });
 
   it('succeeds when project already has targets even with null YAML account/region', async () => {
@@ -769,8 +769,8 @@ agents:
     const result = await handleImport({ source: yamlPath });
 
     expect(result.success).toBe(true);
-    expect(result.importedAgents).toEqual([]);
-    expect(result.importedMemories).toEqual([]);
+    expect(result.success ? result.importedAgents : undefined).toEqual([]);
+    expect(result.success ? result.importedMemories : undefined).toEqual([]);
   });
 
   it('does not write targets when YAML has account/region but no physical IDs', async () => {
@@ -816,7 +816,7 @@ agents:
     // No physical IDs means target is not written to disk
     expect(mockWriteAWSDeploymentTargets).not.toHaveBeenCalled();
     // But the stackName should still be computed using 'default' fallback
-    expect(result.stackName).toBe('AgentCore-myproject-default');
+    expect(result.success ? result.stackName : undefined).toBe('AgentCore-myproject-default');
   });
 });
 
diff --git a/src/cli/commands/import/__tests__/import-runtime-handler.test.ts b/src/cli/commands/import/__tests__/import-runtime-handler.test.ts
index b4fb7de90..506470d17 100644
--- a/src/cli/commands/import/__tests__/import-runtime-handler.test.ts
+++ b/src/cli/commands/import/__tests__/import-runtime-handler.test.ts
@@ -25,7 +25,7 @@ const mockParseAndValidateArn = vi.fn();
 const mockFindResourceInDeployedState = vi.fn();
 const mockFailResult = vi.fn((...args: unknown[]) => ({
   success: false,
-  error: args[1] as string,
+  error: new Error(args[1] as string),
   resourceType: args[2] as string,
   resourceName: args[3] as string,
   logPath: 'test.log',
@@ -205,8 +205,8 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Could not determine entrypoint');
-      expect(result.error).toContain('--entrypoint');
+      expect(!result.success ? result.error.message : undefined).toContain('Could not determine entrypoint');
+      expect(!result.success ? result.error.message : undefined).toContain('--entrypoint');
     });
 
     it('fails with clear error when entryPoint is undefined', async () => {
@@ -231,7 +231,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Could not determine entrypoint');
+      expect(!result.success ? result.error.message : undefined).toContain('Could not determine entrypoint');
     });
 
     it('fails with clear error when entryPoint is empty array', async () => {
@@ -256,7 +256,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Could not determine entrypoint');
+      expect(!result.success ? result.error.message : undefined).toContain('Could not determine entrypoint');
     });
 
     it('uses --entrypoint flag when provided, bypassing auto-detection', async () => {
@@ -369,7 +369,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Multiple runtimes found');
+      expect(!result.success ? result.error.message : undefined).toContain('Multiple runtimes found');
     });
 
     it('errors when no runtimes exist', async () => {
@@ -382,7 +382,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('No runtimes found');
+      expect(!result.success ? result.error.message : undefined).toContain('No runtimes found');
     });
   });
 
@@ -546,7 +546,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('--code');
+      expect(!result.success ? result.error.message : undefined).toContain('--code');
     });
 
     it('fails when source path does not exist', async () => {
@@ -574,7 +574,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('does not exist');
+      expect(!result.success ? result.error.message : undefined).toContain('does not exist');
     });
 
     it('fails when runtime name already exists in project', async () => {
@@ -606,7 +606,7 @@ describe('handleImportRuntime', () => {
       });
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('already exists');
+      expect(!result.success ? result.error.message : undefined).toContain('already exists');
     });
   });
 });
diff --git a/src/cli/commands/import/__tests__/phase-failure-rollback.test.ts b/src/cli/commands/import/__tests__/phase-failure-rollback.test.ts
index 149d65faf..d3bc9e4a3 100644
--- a/src/cli/commands/import/__tests__/phase-failure-rollback.test.ts
+++ b/src/cli/commands/import/__tests__/phase-failure-rollback.test.ts
@@ -250,7 +250,7 @@ describe('Config Rollback on Import Failure', () => {
     const result = await handleImport({ source: '/tmp/config.yaml' });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Phase 1 failed');
+    expect(!result.success ? result.error.message : undefined).toContain('Phase 1 failed');
 
     // First call = merge write, second call = rollback with original (empty) runtimes
     expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
@@ -266,7 +266,7 @@ describe('Config Rollback on Import Failure', () => {
     const result = await handleImport({ source: '/tmp/config.yaml' });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Phase 2 failed');
+    expect(!result.success ? result.error.message : undefined).toContain('Phase 2 failed');
 
     expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
     const rollbackData = mockConfigIOInstance.writeProjectSpec.mock.calls[1]![0];
@@ -281,7 +281,7 @@ describe('Config Rollback on Import Failure', () => {
     const result = await handleImport({ source: '/tmp/config.yaml' });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('CDK build failed');
+    expect(!result.success ? result.error.message : undefined).toContain('CDK build failed');
 
     expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
     const rollbackData = mockConfigIOInstance.writeProjectSpec.mock.calls[1]![0];
@@ -312,7 +312,7 @@ describe('Config Rollback on Import Failure', () => {
     const result = await handleImport({ source: '/tmp/config.yaml' });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No agents found');
+    expect(!result.success ? result.error.message : undefined).toContain('No agents found');
     // Config was never written, so no rollback
     expect(mockConfigIOInstance.writeProjectSpec).not.toHaveBeenCalled();
   });
@@ -339,7 +339,7 @@ describe('Config Rollback on Import Failure', () => {
     const result = await handleImport({ source: '/tmp/config.yaml' });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Could not read deployed template');
+    expect(!result.success ? result.error.message : undefined).toContain('Could not read deployed template');
 
     expect(mockConfigIOInstance.writeProjectSpec).toHaveBeenCalledTimes(2);
     const rollbackData = mockConfigIOInstance.writeProjectSpec.mock.calls[1]![0];
diff --git a/src/cli/commands/import/actions.ts b/src/cli/commands/import/actions.ts
index 71eb70f83..7352b30df 100644
--- a/src/cli/commands/import/actions.ts
+++ b/src/cli/commands/import/actions.ts
@@ -124,9 +124,10 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
     logger.startStep('Validate project context');
     const configRoot = findConfigRoot(process.cwd());
     if (!configRoot) {
-      const error =
-        'No agentcore project found in the current directory.\nRun `agentcore create <name>` first, then run import from inside the project.';
-      logger.endStep('error', error);
+      const error = new Error(
+        'No agentcore project found in the current directory.\nRun `agentcore create <name>` first, then run import from inside the project.'
+      );
+      logger.endStep('error', error.message);
       logger.finalize(false);
       return {
         success: false,
@@ -157,8 +158,8 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
     const parsed = parseStarterToolkitYaml(source);
 
     if (parsed.agents.length === 0) {
-      const error = 'No agents found in the YAML config';
-      logger.endStep('error', error);
+      const error = new Error('No agents found in the YAML config');
+      logger.endStep('error', error.message);
       logger.finalize(false);
       return { success: false, error, logPath: logger.getRelativeLogPath() };
     }
@@ -193,9 +194,10 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
       // If no targets exist (CLI-mode create leaves targets empty), create one from YAML info
       if (targets.length === 0) {
         if (!parsed.awsTarget.account || !parsed.awsTarget.region) {
-          const error =
-            'No deployment targets found in project and YAML has no AWS account/region info.\nRun `agentcore deploy` first to set up a target, then re-run import.';
-          logger.endStep('error', error);
+          const error = new Error(
+            'No deployment targets found in project and YAML has no AWS account/region info.\nRun `agentcore deploy` first to set up a target, then re-run import.'
+          );
+          logger.endStep('error', error.message);
           logger.finalize(false);
           return {
             success: false,
@@ -218,8 +220,8 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
         const found = targets.find(t => t.name === options.target);
         if (!found) {
           const names = targets.map(t => `  - ${t.name} (${t.region}, ${t.account})`).join('\n');
-          const error = `Target "${options.target}" not found. Available targets:\n${names}`;
-          logger.endStep('error', error);
+          const error = new Error(`Target "${options.target}" not found. Available targets:\n${names}`);
+          logger.endStep('error', error.message);
           logger.finalize(false);
           return {
             success: false,
@@ -232,8 +234,8 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
         target = targets[0]!;
       } else {
         const names = targets.map(t => `  - ${t.name} (${t.region}, ${t.account})`).join('\n');
-        const error = `Multiple deployment targets found. Specify one with --target:\n${names}`;
-        logger.endStep('error', error);
+        const error = new Error(`Multiple deployment targets found. Specify one with --target:\n${names}`);
+        logger.endStep('error', error.message);
         logger.finalize(false);
         return {
           success: false,
@@ -498,8 +500,8 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
 
     // At this point we know hasPhysicalIds is true, so target must be defined.
     if (!target) {
-      const error = 'No deployment target available for import.';
-      logger.endStep('error', error);
+      const error = new Error('No deployment target available for import.');
+      logger.endStep('error', error.message);
       logger.finalize(false);
       return { success: false, error, logPath: logger.getRelativeLogPath() };
     }
@@ -636,9 +638,9 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
     }
 
     if (!pipelineResult.success) {
-      const error = pipelineResult.error!;
+      const error = pipelineResult.error;
       await rollbackConfig();
-      logger.endStep('error', error);
+      logger.endStep('error', error.message);
       logger.finalize(false);
       return { success: false, error, logPath: logger.getRelativeLogPath() };
     }
@@ -658,6 +660,6 @@ export async function handleImport(options: ImportOptions): Promise<ImportResult
     await rollbackConfig();
     logger.log(message, 'error');
     logger.finalize(false);
-    return { success: false, error: message, logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(message), logPath: logger.getRelativeLogPath() };
   }
 }
diff --git a/src/cli/commands/import/command.ts b/src/cli/commands/import/command.ts
index 381167aaa..1f5fe81cc 100644
--- a/src/cli/commands/import/command.ts
+++ b/src/cli/commands/import/command.ts
@@ -140,7 +140,7 @@ export const registerImport = (program: Command) => {
           console.log(`Log: ${result.logPath}`);
         }
       } else {
-        console.error(`\n\x1b[31m[error]${reset} Import failed: ${result.error}`);
+        console.error(`\n\x1b[31m[error]${reset} Import failed: ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-evaluator.ts b/src/cli/commands/import/import-evaluator.ts
index 7c6c8b0d2..31a6f1d2f 100644
--- a/src/cli/commands/import/import-evaluator.ts
+++ b/src/cli/commands/import/import-evaluator.ts
@@ -151,7 +151,7 @@ export function registerImportEvaluator(importCmd: Command): void {
         console.log(`  ID: ${result.resourceId}`);
         console.log('');
       } else {
-        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error}`);
+        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-gateway.ts b/src/cli/commands/import/import-gateway.ts
index 3c2384e03..f78c63c9d 100644
--- a/src/cli/commands/import/import-gateway.ts
+++ b/src/cli/commands/import/import-gateway.ts
@@ -608,7 +608,7 @@ export async function handleImportGateway(options: ImportResourceOptions): Promi
 
     if (!pipelineResult.success) {
       await rollback();
-      logger.endStep('error', pipelineResult.error);
+      logger.endStep('error', pipelineResult.error.message);
       logger.finalize(false);
       return {
         success: false,
@@ -638,7 +638,7 @@ export async function handleImportGateway(options: ImportResourceOptions): Promi
     }
     return {
       success: false,
-      error: message,
+      error: new Error(message),
       resourceType: 'gateway',
       resourceName: options.name ?? '',
       logPath: importCtx?.logger.getRelativeLogPath(),
@@ -680,7 +680,7 @@ export function registerImportGateway(importCmd: Command): void {
         console.log(`  agentcore fetch access  ${ANSI.dim}Get gateway URL and token${ANSI.reset}`);
         console.log('');
       } else {
-        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error}`);
+        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-memory.ts b/src/cli/commands/import/import-memory.ts
index 2362d1353..02213c9f1 100644
--- a/src/cli/commands/import/import-memory.ts
+++ b/src/cli/commands/import/import-memory.ts
@@ -121,7 +121,7 @@ export function registerImportMemory(importCmd: Command): void {
         console.log(`  ID: ${result.resourceId}`);
         console.log('');
       } else {
-        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error}`);
+        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-online-eval.ts b/src/cli/commands/import/import-online-eval.ts
index 99935ecdf..b43fa174a 100644
--- a/src/cli/commands/import/import-online-eval.ts
+++ b/src/cli/commands/import/import-online-eval.ts
@@ -209,7 +209,7 @@ export function registerImportOnlineEval(importCmd: Command): void {
         console.log(`  ID: ${result.resourceId}`);
         console.log('');
       } else {
-        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error}`);
+        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-pipeline.ts b/src/cli/commands/import/import-pipeline.ts
index 75b9c70dd..e064a6bfe 100644
--- a/src/cli/commands/import/import-pipeline.ts
+++ b/src/cli/commands/import/import-pipeline.ts
@@ -1,4 +1,5 @@
 import type { ConfigIO } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import type { AwsDeploymentTarget } from '../../../schema';
 import { LocalCdkProject } from '../../cdk/local-cdk-project';
 import { silentIoHost } from '../../cdk/toolkit-lib';
@@ -27,12 +28,10 @@ export interface CdkImportPipelineInput {
   deployedStateEntries: ImportedResource[];
 }
 
-export interface CdkImportPipelineResult {
-  success: boolean;
-  error?: string;
+export type CdkImportPipelineResult = Result & {
   /** True when buildResourcesToImport returned an empty list. Callers decide if this is an error. */
   noResources?: boolean;
-}
+};
 
 /**
  * Shared CDK import pipeline: build → synth → bootstrap → publish assets → phase 1 → phase 2 → update state.
@@ -73,7 +72,7 @@ export async function executeCdkImportPipeline(input: CdkImportPipelineInput): P
     const files = fs.readdirSync(assemblyDirectory).filter((f: string) => f.endsWith('.template.json'));
     if (files.length === 0) {
       await toolkitWrapper.dispose();
-      return { success: false, error: 'No CloudFormation template found in CDK assembly' };
+      return { success: false, error: new Error('No CloudFormation template found in CDK assembly') };
     }
     synthTemplate = JSON.parse(fs.readFileSync(path.join(assemblyDirectory, files[0]!), 'utf-8')) as CfnTemplate;
   }
@@ -103,14 +102,14 @@ export async function executeCdkImportPipeline(input: CdkImportPipelineInput): P
   });
 
   if (!phase1Result.success) {
-    return { success: false, error: `Phase 1 failed: ${phase1Result.error}` };
+    return { success: false, error: new Error(`Phase 1 failed: ${phase1Result.error.message}`) };
   }
 
   // 6. Read deployed template
   onProgress('Reading deployed template...');
   const deployedTemplate = await getDeployedTemplate(target.region, stackName);
   if (!deployedTemplate) {
-    return { success: false, error: 'Could not read deployed template after Phase 1' };
+    return { success: false, error: new Error('Could not read deployed template after Phase 1') };
   }
 
   // 7. Build resources to import (caller-specific logic)
@@ -133,7 +132,7 @@ export async function executeCdkImportPipeline(input: CdkImportPipelineInput): P
   });
 
   if (!phase2Result.success) {
-    return { success: false, error: `Phase 2 failed: ${phase2Result.error}` };
+    return { success: false, error: new Error(`Phase 2 failed: ${phase2Result.error.message}`) };
   }
 
   // 9. Update deployed state
diff --git a/src/cli/commands/import/import-runtime.ts b/src/cli/commands/import/import-runtime.ts
index b1921d546..ff6ba0640 100644
--- a/src/cli/commands/import/import-runtime.ts
+++ b/src/cli/commands/import/import-runtime.ts
@@ -225,7 +225,7 @@ export function registerImportRuntime(importCmd: Command): void {
         console.log(`  agentcore invoke     ${ANSI.dim}Test your agent${ANSI.reset}`);
         console.log('');
       } else {
-        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error}`);
+        console.error(`\n${ANSI.red}[error]${ANSI.reset} ${result.error.message}`);
         if (result.logPath) {
           console.error(`Log: ${result.logPath}`);
         }
diff --git a/src/cli/commands/import/import-utils.ts b/src/cli/commands/import/import-utils.ts
index 5829bbc6c..e29ada5ee 100644
--- a/src/cli/commands/import/import-utils.ts
+++ b/src/cli/commands/import/import-utils.ts
@@ -67,7 +67,7 @@ export function failResult(
   logger.finalize(false);
   return {
     success: false,
-    error,
+    error: new Error(error),
     resourceType,
     resourceName,
     logPath: logger.getRelativeLogPath(),
diff --git a/src/cli/commands/import/phase1-update.ts b/src/cli/commands/import/phase1-update.ts
index 38d622c6b..67128b91d 100644
--- a/src/cli/commands/import/phase1-update.ts
+++ b/src/cli/commands/import/phase1-update.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws/account';
 import type { CfnTemplate } from './template-utils';
 import { filterCompanionOnlyTemplate } from './template-utils';
@@ -18,11 +19,7 @@ export interface Phase1Options {
   onProgress?: (message: string) => void;
 }
 
-export interface Phase1Result {
-  success: boolean;
-  stackExists: boolean;
-  error?: string;
-}
+export type Phase1Result = Result & { stackExists: boolean };
 
 /**
  * Phase 1: UPDATE (pre-import)
@@ -89,7 +86,7 @@ export async function executePhase1(options: Phase1Options): Promise<Phase1Resul
         onProgress?.('Stack already has companion resources, no update needed');
         return { success: true, stackExists: true };
       }
-      return { success: false, stackExists: true, error: message };
+      return { success: false, stackExists: true, error: new Error(message) };
     }
   } else {
     onProgress?.(`Creating stack ${stackName} with companion resources...`);
@@ -114,7 +111,7 @@ export async function executePhase1(options: Phase1Options): Promise<Phase1Resul
       onProgress?.('Phase 1 CREATE complete');
     } catch (err: unknown) {
       const message = err instanceof Error ? err.message : String(err);
-      return { success: false, stackExists: false, error: message };
+      return { success: false, stackExists: false, error: new Error(message) };
     }
   }
 
diff --git a/src/cli/commands/import/phase2-import.ts b/src/cli/commands/import/phase2-import.ts
index d898785f3..b67161df7 100644
--- a/src/cli/commands/import/phase2-import.ts
+++ b/src/cli/commands/import/phase2-import.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws/account';
 import type { CfnTemplate } from './template-utils';
 import { buildImportTemplate } from './template-utils';
@@ -26,10 +27,7 @@ export interface Phase2Options {
   onProgress?: (message: string) => void;
 }
 
-export interface Phase2Result {
-  success: boolean;
-  error?: string;
-}
+export type Phase2Result = Result;
 
 /**
  * Phase 2: IMPORT
@@ -125,11 +123,13 @@ export async function executePhase2(options: Phase2Options): Promise<Phase2Resul
       const existingStack = alreadyInStackMatch[2];
       return {
         success: false,
-        error: `Resource "${resourceId}" is already managed by CloudFormation stack "${existingStack}". It must be removed from that stack before importing into this project.`,
+        error: new Error(
+          `Resource "${resourceId}" is already managed by CloudFormation stack "${existingStack}". It must be removed from that stack before importing into this project.`
+        ),
       };
     }
 
-    return { success: false, error: `Import change set failed: ${message}` };
+    return { success: false, error: new Error(`Import change set failed: ${message}`) };
   }
 }
 
diff --git a/src/cli/commands/import/resource-import.ts b/src/cli/commands/import/resource-import.ts
index a21a160ec..163bbea18 100644
--- a/src/cli/commands/import/resource-import.ts
+++ b/src/cli/commands/import/resource-import.ts
@@ -224,7 +224,7 @@ export async function executeResourceImport<TDetail, TSummary>(
 
     if (!pipelineResult.success) {
       await rollback();
-      logger.endStep('error', pipelineResult.error);
+      logger.endStep('error', pipelineResult.error.message);
       logger.finalize(false);
       return {
         success: false,
@@ -254,7 +254,7 @@ export async function executeResourceImport<TDetail, TSummary>(
     }
     return {
       success: false,
-      error: message,
+      error: new Error(message),
       resourceType: descriptor.resourceType,
       resourceName: options.name ?? '',
       logPath: importCtx?.logger.getRelativeLogPath(),
diff --git a/src/cli/commands/import/types.ts b/src/cli/commands/import/types.ts
index 5d99c79c1..8102b3c18 100644
--- a/src/cli/commands/import/types.ts
+++ b/src/cli/commands/import/types.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import type {
   AgentCoreProjectSpec,
   AuthorizerConfig,
@@ -89,27 +90,21 @@ export interface ResourceToImport {
 /**
  * Result of the import command.
  */
-export interface ImportResult {
-  success: boolean;
-  error?: string;
+export type ImportResult = Result<{
   projectSpec?: AgentCoreProjectSpec;
   importedAgents?: string[];
   importedMemories?: string[];
   stackName?: string;
-  logPath?: string;
-}
+}> & { logPath?: string };
 
 /**
  * Result for single-resource import (runtime, memory, evaluator, etc.).
  */
-export interface ImportResourceResult {
-  success: boolean;
-  error?: string;
+export type ImportResourceResult = Result<{ resourceId?: string }> & {
   resourceType: ImportableResourceType;
   resourceName: string;
-  resourceId?: string;
   logPath?: string;
-}
+};
 
 /**
  * Options shared across import subcommands.
diff --git a/src/cli/commands/invoke/action.ts b/src/cli/commands/invoke/action.ts
index eb7aaaac2..e38e85ec7 100644
--- a/src/cli/commands/invoke/action.ts
+++ b/src/cli/commands/invoke/action.ts
@@ -43,41 +43,50 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
   // Resolve target
   const targetNames = Object.keys(deployedState.targets);
   if (targetNames.length === 0) {
-    return { success: false, error: 'No deployed targets found. Run `agentcore deploy` first.' };
+    return { success: false, error: new Error('No deployed targets found. Run `agentcore deploy` first.') };
   }
 
   const selectedTargetName = options.targetName ?? targetNames[0]!;
 
   if (options.targetName && !targetNames.includes(options.targetName)) {
-    return { success: false, error: `Target '${options.targetName}' not found. Available: ${targetNames.join(', ')}` };
+    return {
+      success: false,
+      error: new Error(`Target '${options.targetName}' not found. Available: ${targetNames.join(', ')}`),
+    };
   }
 
   const targetState = deployedState.targets[selectedTargetName];
   const targetConfig = awsTargets.find(t => t.name === selectedTargetName);
 
   if (!targetConfig) {
-    return { success: false, error: `Target config '${selectedTargetName}' not found in aws-targets` };
+    return { success: false, error: new Error(`Target config '${selectedTargetName}' not found in aws-targets`) };
   }
 
   if (project.runtimes.length === 0) {
-    return { success: false, error: 'No agents defined in configuration' };
+    return { success: false, error: new Error('No agents defined in configuration') };
   }
 
   // Resolve agent
   const agentNames = project.runtimes.map(a => a.name);
 
   if (!options.agentName && project.runtimes.length > 1) {
-    return { success: false, error: `Multiple runtimes found. Use --runtime to specify one: ${agentNames.join(', ')}` };
+    return {
+      success: false,
+      error: new Error(`Multiple runtimes found. Use --runtime to specify one: ${agentNames.join(', ')}`),
+    };
   }
 
   const agentSpec = options.agentName ? project.runtimes.find(a => a.name === options.agentName) : project.runtimes[0];
 
   if (options.agentName && !agentSpec) {
-    return { success: false, error: `Agent '${options.agentName}' not found. Available: ${agentNames.join(', ')}` };
+    return {
+      success: false,
+      error: new Error(`Agent '${options.agentName}' not found. Available: ${agentNames.join(', ')}`),
+    };
   }
 
   if (!agentSpec) {
-    return { success: false, error: 'No agents defined in configuration' };
+    return { success: false, error: new Error('No agents defined in configuration') };
   }
 
   // Warn about VPC mode endpoint requirements
@@ -91,7 +100,10 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
   const agentState = targetState?.resources?.runtimes?.[agentSpec.name];
 
   if (!agentState) {
-    return { success: false, error: `Agent '${agentSpec.name}' is not deployed to target '${selectedTargetName}'` };
+    return {
+      success: false,
+      error: new Error(`Agent '${agentSpec.name}' is not deployed to target '${selectedTargetName}'`),
+    };
   }
 
   // Build config bundle baggage if a bundle is associated with this agent
@@ -118,13 +130,17 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       } catch (err) {
         return {
           success: false,
-          error: `CUSTOM_JWT agent requires a bearer token. Auto-fetch failed: ${err instanceof Error ? err.message : String(err)}\nProvide one manually with --bearer-token.`,
+          error: new Error(
+            `CUSTOM_JWT agent requires a bearer token. Auto-fetch failed: ${err instanceof Error ? err.message : String(err)}\nProvide one manually with --bearer-token.`
+          ),
         };
       }
     } else {
       return {
         success: false,
-        error: `Agent '${agentSpec.name}' is configured for CUSTOM_JWT but no bearer token is available.\nEither provide --bearer-token or re-add the agent with --client-id and --client-secret to enable auto-fetch.`,
+        error: new Error(
+          `Agent '${agentSpec.name}' is configured for CUSTOM_JWT but no bearer token is available.\nEither provide --bearer-token or re-add the agent with --client-id and --client-secret to enable auto-fetch.`
+        ),
       };
     }
   }
@@ -147,7 +163,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
     });
     const command = options.prompt;
     if (!command) {
-      return { success: false, error: '--exec requires a command (prompt)' };
+      return { success: false, error: new Error('--exec requires a command (prompt)') };
     }
     logger.logPrompt(command, options.sessionId, options.userId);
 
@@ -195,8 +211,15 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       logger.logResponse(stdout || stderr || `exit code: ${exitCode}`);
 
       if (options.json) {
+        if (exitCode !== 0) {
+          return {
+            success: false,
+            error: new Error(stderr || `exit code: ${exitCode}`),
+            logFilePath: logger.logFilePath,
+          };
+        }
         return {
-          success: exitCode === 0,
+          success: true,
           agentName: agentSpec.name,
           targetName: selectedTargetName,
           response: JSON.stringify({ stdout, stderr, exitCode, status }),
@@ -207,9 +230,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       if (exitCode === undefined) {
         return {
           success: false,
-          agentName: agentSpec.name,
-          targetName: selectedTargetName,
-          error: 'Command stream ended without exit code',
+          error: new Error('Command stream ended without exit code'),
           logFilePath: logger.logFilePath,
         };
       }
@@ -217,9 +238,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       if (exitCode !== 0) {
         return {
           success: false,
-          agentName: agentSpec.name,
-          targetName: selectedTargetName,
-          error: `Command exited with code ${exitCode}${status === 'TIMED_OUT' ? ' (timed out)' : ''}`,
+          error: new Error(`Command exited with code ${exitCode}${status === 'TIMED_OUT' ? ' (timed out)' : ''}`),
           logFilePath: logger.logFilePath,
         };
       }
@@ -261,7 +280,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       } catch (err) {
         return {
           success: false,
-          error: `Failed to list MCP tools: ${err instanceof Error ? err.message : String(err)}`,
+          error: new Error(`Failed to list MCP tools: ${err instanceof Error ? err.message : String(err)}`),
         };
       }
     }
@@ -271,7 +290,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       if (!options.tool) {
         return {
           success: false,
-          error: 'MCP call-tool requires --tool <name>. Use "list-tools" to see available tools.',
+          error: new Error('MCP call-tool requires --tool <name>. Use "list-tools" to see available tools.'),
         };
       }
       let args: Record<string, unknown> = {};
@@ -279,7 +298,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
         try {
           args = JSON.parse(options.input) as Record<string, unknown>;
         } catch {
-          return { success: false, error: `Invalid JSON for --input: ${options.input}` };
+          return { success: false, error: new Error(`Invalid JSON for --input: ${options.input}`) };
         }
       }
       try {
@@ -295,7 +314,7 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       } catch (err) {
         return {
           success: false,
-          error: `Failed to call MCP tool: ${err instanceof Error ? err.message : String(err)}`,
+          error: new Error(`Failed to call MCP tool: ${err instanceof Error ? err.message : String(err)}`),
         };
       }
     }
@@ -303,14 +322,15 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
     if (!options.prompt) {
       return {
         success: false,
-        error:
-          'MCP agents require a command. Usage:\n  agentcore invoke list-tools\n  agentcore invoke call-tool --tool <name> --input \'{"arg": "value"}\'',
+        error: new Error(
+          'MCP agents require a command. Usage:\n  agentcore invoke list-tools\n  agentcore invoke call-tool --tool <name> --input \'{"arg": "value"}\''
+        ),
       };
     }
   }
 
   if (!options.prompt) {
-    return { success: false, error: 'No prompt provided. Usage: agentcore invoke "your prompt"' };
+    return { success: false, error: new Error('No prompt provided. Usage: agentcore invoke "your prompt"') };
   }
 
   // A2A protocol handling — send JSON-RPC message/send via InvokeAgentRuntime
@@ -343,7 +363,10 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
         response,
       };
     } catch (err) {
-      return { success: false, error: `A2A invoke failed: ${err instanceof Error ? err.message : String(err)}` };
+      return {
+        success: false,
+        error: new Error(`A2A invoke failed: ${err instanceof Error ? err.message : String(err)}`),
+      };
     }
   }
 
@@ -388,8 +411,15 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
 
       logger.logResponse(response);
 
+      if (hasError) {
+        return {
+          success: false,
+          error: new Error(response),
+          logFilePath: logger.logFilePath,
+        };
+      }
       return {
-        success: !hasError,
+        success: true,
         agentName: agentSpec.name,
         targetName: selectedTargetName,
         response,
@@ -398,7 +428,11 @@ export async function handleInvoke(context: InvokeContext, options: InvokeOption
       };
     } catch (err) {
       logger.logError(err, 'AGUI invoke failed');
-      return { success: false, error: `AGUI invoke failed: ${err instanceof Error ? err.message : String(err)}` };
+      return {
+        success: false,
+        error: new Error(`AGUI invoke failed: ${err instanceof Error ? err.message : String(err)}`),
+        logFilePath: logger.logFilePath,
+      };
     }
   }
 
diff --git a/src/cli/commands/invoke/command.tsx b/src/cli/commands/invoke/command.tsx
index cc0cd1e35..619b20a32 100644
--- a/src/cli/commands/invoke/command.tsx
+++ b/src/cli/commands/invoke/command.tsx
@@ -58,7 +58,7 @@ async function handleInvokeCLI(options: InvokeOptions): Promise<void> {
       console.log(JSON.stringify(result));
     } else if (options.stream) {
       // Streaming already wrote to stdout, just show session and log path
-      if (result.sessionId) {
+      if (result.success && result.sessionId) {
         console.error(`\nSession: ${result.sessionId}`);
         console.error(`To resume: agentcore invoke --session-id ${result.sessionId}`);
       }
@@ -72,7 +72,7 @@ async function handleInvokeCLI(options: InvokeOptions): Promise<void> {
       } else if (!result.success && result.error) {
         console.error(result.error);
       }
-      if (result.sessionId) {
+      if (result.success && result.sessionId) {
         console.error(`\nSession: ${result.sessionId}`);
         console.error(`To resume: agentcore invoke --session-id ${result.sessionId}`);
       }
diff --git a/src/cli/commands/invoke/types.ts b/src/cli/commands/invoke/types.ts
index 61401c332..b8c62ede1 100644
--- a/src/cli/commands/invoke/types.ts
+++ b/src/cli/commands/invoke/types.ts
@@ -1,3 +1,5 @@
+import type { Result } from '../../../lib/types';
+
 export interface InvokeOptions {
   agentName?: string;
   targetName?: string;
@@ -22,12 +24,9 @@ export interface InvokeOptions {
   bearerToken?: string;
 }
 
-export interface InvokeResult {
-  success: boolean;
+export type InvokeResult = Result<{
   agentName?: string;
   targetName?: string;
   response?: string;
   sessionId?: string;
-  error?: string;
-  logFilePath?: string;
-}
+}> & { logFilePath?: string };
diff --git a/src/cli/commands/logs/__tests__/action.test.ts b/src/cli/commands/logs/__tests__/action.test.ts
index 07d072320..1cd58c625 100644
--- a/src/cli/commands/logs/__tests__/action.test.ts
+++ b/src/cli/commands/logs/__tests__/action.test.ts
@@ -132,9 +132,9 @@ describe('resolveAgentContext', () => {
     const result = resolveAgentContext(context, {});
     expect(result.success).toBe(false);
     if (!result.success) {
-      expect(result.error).toContain('Multiple runtimes found');
-      expect(result.error).toContain('AgentA');
-      expect(result.error).toContain('AgentB');
+      expect(result.error.message).toContain('Multiple runtimes found');
+      expect(result.error.message).toContain('AgentA');
+      expect(result.error.message).toContain('AgentB');
     }
   });
 
@@ -205,7 +205,7 @@ describe('resolveAgentContext', () => {
     const result = resolveAgentContext(makeContext(), { runtime: 'UnknownAgent' });
     expect(result.success).toBe(false);
     if (!result.success) {
-      expect(result.error).toContain("Runtime 'UnknownAgent' not found");
+      expect(result.error.message).toContain("Runtime 'UnknownAgent' not found");
     }
   });
 
@@ -230,7 +230,7 @@ describe('resolveAgentContext', () => {
     const result = resolveAgentContext(context, {});
     expect(result.success).toBe(false);
     if (!result.success) {
-      expect(result.error).toContain('No runtimes defined');
+      expect(result.error.message).toContain('No runtimes defined');
     }
   });
 
@@ -249,7 +249,7 @@ describe('resolveAgentContext', () => {
     const result = resolveAgentContext(context, {});
     expect(result.success).toBe(false);
     if (!result.success) {
-      expect(result.error).toContain('is not deployed');
+      expect(result.error.message).toContain('is not deployed');
     }
   });
 });
diff --git a/src/cli/commands/logs/action.ts b/src/cli/commands/logs/action.ts
index 72be2c864..7f5a24187 100644
--- a/src/cli/commands/logs/action.ts
+++ b/src/cli/commands/logs/action.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { parseTimeString } from '../../../lib/utils';
 import { searchLogs, streamLogs } from '../../aws/cloudwatch';
 import { DEFAULT_ENDPOINT_NAME } from '../../constants';
@@ -17,10 +18,7 @@ export interface AgentContext {
   logGroupName: string;
 }
 
-export interface LogsResult {
-  success: boolean;
-  error?: string;
-}
+export type LogsResult = Result;
 
 /**
  * Detect whether to stream or search based on options
@@ -49,10 +47,10 @@ export function formatLogLine(event: { timestamp: number; message: string }, jso
 export function resolveAgentContext(
   context: DeployedProjectConfig,
   options: LogsOptions
-): { success: true; agentContext: AgentContext } | { success: false; error: string } {
+): Result<{ agentContext: AgentContext }> {
   const result = resolveAgent(context, options);
   if (!result.success) {
-    return { success: false, error: result.error };
+    return result;
   }
   const { agent } = result;
   const endpointName = DEFAULT_ENDPOINT_NAME;
@@ -78,7 +76,7 @@ export async function handleLogs(options: LogsOptions): Promise<LogsResult> {
   if (options.level && !VALID_LEVELS.includes(options.level.toLowerCase())) {
     return {
       success: false,
-      error: `Invalid log level: "${options.level}". Valid levels: ${VALID_LEVELS.join(', ')}`,
+      error: new Error(`Invalid log level: "${options.level}". Valid levels: ${VALID_LEVELS.join(', ')}`),
     };
   }
 
@@ -96,7 +94,7 @@ export async function handleLogs(options: LogsOptions): Promise<LogsResult> {
   try {
     filterPattern = buildFilterPattern({ level: options.level, query: options.query });
   } catch (err) {
-    return { success: false, error: (err as Error).message };
+    return { success: false, error: err as Error };
   }
 
   const mode = detectMode(options);
@@ -143,7 +141,7 @@ export async function handleLogs(options: LogsOptions): Promise<LogsResult> {
     if (errorName === 'ResourceNotFoundException') {
       return {
         success: false,
-        error: `No logs found for agent '${agentContext.agentName}'. Has the agent been invoked?`,
+        error: new Error(`No logs found for agent '${agentContext.agentName}'. Has the agent been invoked?`),
       };
     }
 
diff --git a/src/cli/commands/logs/command.tsx b/src/cli/commands/logs/command.tsx
index 05649887d..ba6d1ef21 100644
--- a/src/cli/commands/logs/command.tsx
+++ b/src/cli/commands/logs/command.tsx
@@ -34,7 +34,7 @@ export const registerLogs = (program: Command) => {
         const result = await handleLogs(cliOptions);
 
         if (!result.success) {
-          render(<Text color="red">{result.error}</Text>);
+          render(<Text color="red">{result.error.message}</Text>);
           process.exit(1);
         }
       } catch (error) {
@@ -59,7 +59,7 @@ export const registerLogs = (program: Command) => {
         const result = await handleLogsEval(cliOptions);
 
         if (!result.success) {
-          render(<Text color="red">{result.error}</Text>);
+          render(<Text color="red">{result.error.message}</Text>);
           process.exit(1);
         }
       } catch (error) {
diff --git a/src/cli/commands/package/action.ts b/src/cli/commands/package/action.ts
index 5a99baa05..7c528b492 100644
--- a/src/cli/commands/package/action.ts
+++ b/src/cli/commands/package/action.ts
@@ -6,6 +6,7 @@ import {
   resolveCodeLocation,
   validateAgentExists,
 } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import type { AgentCoreProjectSpec } from '../../../schema';
 import { join, resolve } from 'path';
 
@@ -40,12 +41,7 @@ export interface PackageAgentResult {
   sizeMb: string;
 }
 
-export interface PackageResult {
-  success: boolean;
-  results: PackageAgentResult[];
-  skipped: string[];
-  error?: string;
-}
+export type PackageResult = Result & { results: PackageAgentResult[]; skipped: string[] };
 
 export async function handlePackage(context: PackageContext): Promise<PackageResult> {
   const { project, configBaseDir, targetAgent } = context;
diff --git a/src/cli/commands/pause/command.tsx b/src/cli/commands/pause/command.tsx
index 82a79bccf..e72fe032f 100644
--- a/src/cli/commands/pause/command.tsx
+++ b/src/cli/commands/pause/command.tsx
@@ -55,7 +55,7 @@ function registerOnlineEvalSubcommand(parent: Command, action: 'pause' | 'resume
           const displayName = cliOptions.arn ? result.configId : name;
           console.log(`${pastTense} online eval config "${displayName}" (status: ${result.executionStatus})`);
         } else {
-          render(<Text color="red">{result.error}</Text>);
+          render(<Text color="red">{result.error.message}</Text>);
         }
 
         process.exit(result.success ? 0 : 1);
diff --git a/src/cli/commands/remove/command.tsx b/src/cli/commands/remove/command.tsx
index 05e532688..ca26b2826 100644
--- a/src/cli/commands/remove/command.tsx
+++ b/src/cli/commands/remove/command.tsx
@@ -48,14 +48,14 @@ async function handleRemoveAll(_options: RemoveAllOptions): Promise<RemoveResult
       note: 'Your source code has not been modified. Run `agentcore deploy` to apply changes to AWS.',
     };
   } catch (err) {
-    return { success: false, error: getErrorMessage(err) };
+    return { success: false, error: new Error(getErrorMessage(err)) };
   }
 }
 
 async function handleRemoveAllCLI(options: RemoveAllOptions): Promise<void> {
   validateRemoveAllOptions(options);
   const result = await handleRemoveAll(options);
-  console.log(JSON.stringify(result));
+  console.log(JSON.stringify(result.success ? result : { ...result, error: result.error.message }));
   process.exit(result.success ? 0 : 1);
 }
 
diff --git a/src/cli/commands/remove/types.ts b/src/cli/commands/remove/types.ts
index 9a30f5e24..c6832c121 100644
--- a/src/cli/commands/remove/types.ts
+++ b/src/cli/commands/remove/types.ts
@@ -1,3 +1,5 @@
+import type { Result } from '../../../lib/types';
+
 export type ResourceType =
   | 'agent'
   | 'gateway'
@@ -25,11 +27,9 @@ export interface RemoveAllOptions {
   json?: boolean;
 }
 
-export interface RemoveResult {
-  success: boolean;
+export type RemoveResult = Result<{
   resourceType?: ResourceType;
   resourceName?: string;
   message?: string;
   note?: string;
-  error?: string;
-}
+}>;
diff --git a/src/cli/commands/run/command.tsx b/src/cli/commands/run/command.tsx
index e5ba8ca59..7afc646e1 100644
--- a/src/cli/commands/run/command.tsx
+++ b/src/cli/commands/run/command.tsx
@@ -25,7 +25,7 @@ const RECOMMENDATION_TYPE_MAP: Record<string, RecommendationType> = {
 };
 
 function formatRunOutput(result: Awaited<ReturnType<typeof handleRunEval>>): void {
-  if (!result.run) return;
+  if (!result.success) return;
 
   const { run } = result;
   const date = new Date(run.timestamp).toLocaleString([], {
@@ -151,7 +151,7 @@ export const registerRun = (program: Command) => {
             formatRunOutput(result);
           } else {
             formatRunOutput(result);
-            render(<Text color="red">{result.error}</Text>);
+            render(<Text color="red">{result.error.message}</Text>);
           }
 
           process.exit(result.success ? 0 : 1);
@@ -244,7 +244,7 @@ export const registerRun = (program: Command) => {
           } else if (result.success) {
             formatBatchEvalOutput(result);
           } else {
-            render(<Text color="red">{result.error}</Text>);
+            render(<Text color="red">{result.error.message}</Text>);
             if (result.logFilePath) {
               console.error(`\nLog: ${result.logFilePath}`);
             }
@@ -403,7 +403,7 @@ export const registerRun = (program: Command) => {
             if (cliOptions.json) {
               console.log(JSON.stringify(result));
             } else {
-              render(<Text color="red">{result.error}</Text>);
+              render(<Text color="red">{result.error.message}</Text>);
               if (result.logFilePath) {
                 console.error(`\nLog: ${result.logFilePath}`);
               }
@@ -495,7 +495,7 @@ function formatBatchEvalOutput(result: RunBatchEvaluationCommandResult): void {
   console.log(`Status: ${result.status}`);
 
   // Show session stats from API if available
-  const evalResults = result.evaluationResults;
+  const evalResults = result.success ? result.evaluationResults : undefined;
   if (evalResults) {
     const parts: string[] = [];
     if (evalResults.totalNumberOfSessions != null) parts.push(`${evalResults.totalNumberOfSessions} sessions`);
diff --git a/src/cli/commands/status/action.ts b/src/cli/commands/status/action.ts
index 271b05bc9..bd5a121bc 100644
--- a/src/cli/commands/status/action.ts
+++ b/src/cli/commands/status/action.ts
@@ -1,4 +1,5 @@
 import { ConfigIO } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import type { AgentCoreProjectSpec, AwsDeploymentTargets, DeployedResourceState, DeployedState } from '../../../schema';
 import { getAgentRuntimeStatus } from '../../aws';
 import { getEvaluator, getOnlineEvaluationConfig } from '../../aws/agentcore-control';
@@ -32,15 +33,12 @@ export interface ResourceStatusEntry {
   invocationUrl?: string;
 }
 
-export interface ProjectStatusResult {
-  success: boolean;
+export type ProjectStatusResult = Result<{ targetRegion?: string }> & {
   projectName: string;
   targetName: string;
-  targetRegion?: string;
   resources: ResourceStatusEntry[];
-  error?: string;
   logPath?: string;
-}
+};
 
 export interface StatusContext {
   project: AgentCoreProjectSpec;
@@ -48,14 +46,11 @@ export interface StatusContext {
   awsTargets: AwsDeploymentTargets;
 }
 
-export interface RuntimeLookupResult {
-  success: boolean;
+export type RuntimeLookupResult = Result<{
   targetName?: string;
   runtimeId?: string;
   runtimeStatus?: string;
-  error?: string;
-  logPath?: string;
-}
+}> & { logPath?: string };
 
 /**
  * Loads configuration required for status check.
@@ -336,7 +331,7 @@ export async function handleProjectStatus(
       projectName: project.name,
       targetName: options.targetName,
       resources: [],
-      error,
+      error: new Error(error),
       logPath: logger.getRelativeLogPath(),
     };
   }
@@ -504,7 +499,7 @@ export async function handleRuntimeLookup(
     const error = 'No deployment targets found. Run `agentcore create` first.';
     logger.endStep('error', error);
     logger.finalize(false);
-    return { success: false, error, logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(error), logPath: logger.getRelativeLogPath() };
   }
 
   const selectedTargetName = options.targetName ?? targetNames[0]!;
@@ -513,7 +508,7 @@ export async function handleRuntimeLookup(
     const error = `Target '${options.targetName}' not found. Available: ${targetNames.join(', ')}`;
     logger.endStep('error', error);
     logger.finalize(false);
-    return { success: false, error, logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(error), logPath: logger.getRelativeLogPath() };
   }
 
   const targetConfig = awsTargets.find(target => target.name === selectedTargetName);
@@ -522,7 +517,7 @@ export async function handleRuntimeLookup(
     const error = `Target config '${selectedTargetName}' not found in aws-targets`;
     logger.endStep('error', error);
     logger.finalize(false);
-    return { success: false, error, logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(error), logPath: logger.getRelativeLogPath() };
   }
 
   logger.log(`Target: ${selectedTargetName} (${targetConfig.region})`);
@@ -550,6 +545,6 @@ export async function handleRuntimeLookup(
     const errorMsg = getErrorMessage(error);
     logger.endStep('error', errorMsg);
     logger.finalize(false);
-    return { success: false, error: errorMsg, logPath: logger.getRelativeLogPath() };
+    return { success: false, error: new Error(errorMsg), logPath: logger.getRelativeLogPath() };
   }
 }
diff --git a/src/cli/commands/status/command.tsx b/src/cli/commands/status/command.tsx
index 506ad10ec..083df19a6 100644
--- a/src/cli/commands/status/command.tsx
+++ b/src/cli/commands/status/command.tsx
@@ -105,7 +105,7 @@ export const registerStatus = (program: Command) => {
           }
 
           if (!result.success) {
-            render(<Text color="red">{result.error}</Text>);
+            render(<Text color="red">{result.error.message}</Text>);
             return;
           }
 
@@ -132,7 +132,7 @@ export const registerStatus = (program: Command) => {
         }
 
         if (!result.success) {
-          render(<Text color="red">{result.error}</Text>);
+          render(<Text color="red">{result.error.message}</Text>);
           return;
         }
 
diff --git a/src/cli/commands/traces/action.ts b/src/cli/commands/traces/action.ts
index d761cd4b7..8c5fe3c65 100644
--- a/src/cli/commands/traces/action.ts
+++ b/src/cli/commands/traces/action.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { parseTimeString } from '../../../lib/utils';
 import type { DeployedProjectConfig } from '../../operations/resolve-agent';
 import { resolveAgent } from '../../operations/resolve-agent';
@@ -19,7 +20,7 @@ export async function handleTracesList(
 ): Promise<TracesListResult> {
   const resolved = resolveAgent(context, options);
   if (!resolved.success) {
-    return { success: false, error: resolved.error };
+    return { success: false, error: resolved.error.message };
   }
 
   const { agent } = resolved;
@@ -56,7 +57,7 @@ export async function handleTracesList(
   });
 
   if (!result.success) {
-    return { success: false, error: result.error, consoleUrl };
+    return { success: false, error: result.error.message, consoleUrl };
   }
 
   return {
@@ -68,14 +69,11 @@ export async function handleTracesList(
   };
 }
 
-export interface TracesGetResult {
-  success: boolean;
+export type TracesGetResult = Result<{
   agentName?: string;
   targetName?: string;
-  consoleUrl?: string;
   filePath?: string;
-  error?: string;
-}
+}> & { consoleUrl?: string };
 
 export async function handleTracesGet(
   context: DeployedProjectConfig,
diff --git a/src/cli/commands/traces/command.tsx b/src/cli/commands/traces/command.tsx
index 0222ce419..f9aa2f8b6 100644
--- a/src/cli/commands/traces/command.tsx
+++ b/src/cli/commands/traces/command.tsx
@@ -109,7 +109,7 @@ export const registerTraces = (program: Command) => {
         if (!result.success) {
           render(
             <Box flexDirection="column">
-              <Text color="red">Error: {result.error}</Text>
+              <Text color="red">Error: {result.error.message}</Text>
               {result.consoleUrl && <Text color="gray">Console: {result.consoleUrl}</Text>}
             </Box>
           );
diff --git a/src/cli/commands/validate/__tests__/action.test.ts b/src/cli/commands/validate/__tests__/action.test.ts
index d6774f252..1685f8dd9 100644
--- a/src/cli/commands/validate/__tests__/action.test.ts
+++ b/src/cli/commands/validate/__tests__/action.test.ts
@@ -74,7 +74,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No agentcore project found');
+    expect(!result.success ? result.error.message : undefined).toContain('No agentcore project found');
   });
 
   it('returns success when all configs are valid', async () => {
@@ -95,7 +95,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('invalid project');
+    expect(!result.success ? result.error.message : undefined).toContain('invalid project');
   });
 
   it('returns error when AWS targets fails', async () => {
@@ -106,7 +106,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('bad targets');
+    expect(!result.success ? result.error.message : undefined).toContain('bad targets');
   });
 
   it('validates state file when it exists', async () => {
@@ -132,7 +132,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('bad state');
+    expect(!result.success ? result.error.message : undefined).toContain('bad state');
   });
 
   it('uses custom directory when provided', async () => {
@@ -155,7 +155,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('field "name" is required');
+    expect(!result.success ? result.error.message : undefined).toBe('field "name" is required');
   });
 
   it('formats ConfigParseError with cause', async () => {
@@ -166,8 +166,8 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Invalid JSON in agentcore.json');
-    expect(result.error).toContain('Unexpected token');
+    expect(!result.success ? result.error.message : undefined).toContain('Invalid JSON in agentcore.json');
+    expect(!result.success ? result.error.message : undefined).toContain('Unexpected token');
   });
 
   it('formats ConfigReadError with cause', async () => {
@@ -180,8 +180,8 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Failed to read agentcore.json');
-    expect(result.error).toContain('EACCES');
+    expect(!result.success ? result.error.message : undefined).toContain('Failed to read agentcore.json');
+    expect(!result.success ? result.error.message : undefined).toContain('EACCES');
   });
 
   it('formats ConfigNotFoundError with file name', async () => {
@@ -192,7 +192,7 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('Required file not found: agentcore.json');
+    expect(!result.success ? result.error.message : undefined).toBe('Required file not found: agentcore.json');
   });
 
   it('formats non-Error values as strings', async () => {
@@ -202,6 +202,6 @@ describe('handleValidate', () => {
     const result = await handleValidate({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('string error');
+    expect(!result.success ? result.error.message : undefined).toBe('string error');
   });
 });
diff --git a/src/cli/commands/validate/action.ts b/src/cli/commands/validate/action.ts
index 572f5cf7d..99031c996 100644
--- a/src/cli/commands/validate/action.ts
+++ b/src/cli/commands/validate/action.ts
@@ -7,15 +7,13 @@ import {
   NoProjectError,
   findConfigRoot,
 } from '../../../lib';
+import type { Result } from '../../../lib/types';
 
 export interface ValidateOptions {
   directory?: string;
 }
 
-export interface ValidateResult {
-  success: boolean;
-  error?: string;
-}
+export type ValidateResult = Result;
 
 /**
  * Validates all AgentCore schema files in the project.
@@ -29,7 +27,7 @@ export async function handleValidate(options: ValidateOptions): Promise<Validate
   if (!configRoot) {
     return {
       success: false,
-      error: new NoProjectError().message,
+      error: new NoProjectError(),
     };
   }
 
@@ -39,14 +37,14 @@ export async function handleValidate(options: ValidateOptions): Promise<Validate
   try {
     await configIO.readProjectSpec();
   } catch (err) {
-    return { success: false, error: formatError(err, 'agentcore.json') };
+    return { success: false, error: new Error(formatError(err, 'agentcore.json')) };
   }
 
   // Validate AWS targets (aws-targets.json)
   try {
     await configIO.readAWSDeploymentTargets();
   } catch (err) {
-    return { success: false, error: formatError(err, 'aws-targets.json') };
+    return { success: false, error: new Error(formatError(err, 'aws-targets.json')) };
   }
 
   // Validate deployed state if it exists (.cli/state.json)
@@ -54,7 +52,7 @@ export async function handleValidate(options: ValidateOptions): Promise<Validate
     try {
       await configIO.readDeployedState();
     } catch (err) {
-      return { success: false, error: formatError(err, '.cli/state.json') };
+      return { success: false, error: new Error(formatError(err, '.cli/state.json')) };
     }
   }
 
diff --git a/src/cli/commands/validate/command.tsx b/src/cli/commands/validate/command.tsx
index b4149a804..7f2fb2bff 100644
--- a/src/cli/commands/validate/command.tsx
+++ b/src/cli/commands/validate/command.tsx
@@ -15,7 +15,7 @@ export const registerValidate = (program: Command) => {
         render(<Text color="green">Valid</Text>);
         process.exit(0);
       } else {
-        render(<Text color="red">{result.error}</Text>);
+        render(<Text color="red">{result.error.message}</Text>);
         process.exit(1);
       }
     });
diff --git a/src/cli/operations/agent/import/index.ts b/src/cli/operations/agent/import/index.ts
index e49d9e3c0..e3226bdba 100644
--- a/src/cli/operations/agent/import/index.ts
+++ b/src/cli/operations/agent/import/index.ts
@@ -9,7 +9,7 @@ import { getBedrockAgentConfig } from '../../../aws/bedrock-import';
 import { getErrorMessage } from '../../../errors';
 import type { JwtConfigOptions } from '../../../primitives/auth-utils';
 import { createManagedOAuthCredential } from '../../../primitives/auth-utils';
-import type { AddResult } from '../../../primitives/types';
+import type { Result } from '../../../primitives/types';
 import type { MemoryOption } from '../../../tui/screens/generate/types';
 import { setupPythonProject } from '../../python';
 import { writeAgentToProject } from '../generate/write-agent-to-project';
@@ -36,7 +36,7 @@ export interface ExecuteImportAgentParams {
 
 export async function executeImportAgent(
   params: ExecuteImportAgentParams
-): Promise<AddResult<{ agentName: string; agentPath: string }>> {
+): Promise<Result<{ agentName: string; agentPath: string }>> {
   const {
     name,
     framework,
@@ -120,6 +120,6 @@ export async function executeImportAgent(
 
     return { success: true, agentName: name, agentPath };
   } catch (err) {
-    return { success: false, error: getErrorMessage(err) };
+    return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
   }
 }
diff --git a/src/cli/operations/deploy/post-deploy-observability.ts b/src/cli/operations/deploy/post-deploy-observability.ts
index 0616a65dc..b153a376e 100644
--- a/src/cli/operations/deploy/post-deploy-observability.ts
+++ b/src/cli/operations/deploy/post-deploy-observability.ts
@@ -1,4 +1,5 @@
 import { readGlobalConfigSync } from '../../../lib/schemas/io/global-config';
+import type { Result } from '../../../lib/types';
 import { enableTransactionSearch } from '../../aws/transaction-search';
 
 export interface TransactionSearchSetupOptions {
@@ -8,10 +9,7 @@ export interface TransactionSearchSetupOptions {
   hasGateways?: boolean;
 }
 
-export interface TransactionSearchSetupResult {
-  success: boolean;
-  error?: string;
-}
+export type TransactionSearchSetupResult = Result;
 
 /**
  * Post-deploy step: enable CloudWatch Transaction Search (Application Signals +
diff --git a/src/cli/operations/deploy/teardown.ts b/src/cli/operations/deploy/teardown.ts
index 2e38f2576..8373448e3 100644
--- a/src/cli/operations/deploy/teardown.ts
+++ b/src/cli/operations/deploy/teardown.ts
@@ -1,4 +1,5 @@
 import { CONFIG_DIR, ConfigIO } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import type { AwsDeploymentTarget } from '../../../schema';
 import { withTargetRegion } from '../../aws';
 import { deleteConfigurationBundle } from '../../aws/agentcore-config-bundles';
@@ -99,10 +100,7 @@ export function getCdkProjectDir(cwd?: string): string {
   return join(baseDir, CONFIG_DIR, 'cdk');
 }
 
-export interface StackTeardownResult {
-  success: boolean;
-  error?: string;
-}
+export type StackTeardownResult = Result;
 
 /**
  * Perform full stack teardown for a target: destroy CloudFormation stack,
diff --git a/src/cli/operations/dev/web-ui/web-server.ts b/src/cli/operations/dev/web-ui/web-server.ts
index 2b20b2d07..c7fa72e19 100644
--- a/src/cli/operations/dev/web-ui/web-server.ts
+++ b/src/cli/operations/dev/web-ui/web-server.ts
@@ -89,7 +89,7 @@ export type ListCloudWatchTracesHandler = (
   harnessName: string | undefined,
   startTime?: number,
   endTime?: number
-) => Promise<{ success: boolean; traces?: unknown[]; error?: string }>;
+) => Promise<{ success: boolean; traces?: unknown[]; error?: string | Error }>;
 
 /**
  * Custom handler for GET /api/cloudwatch-traces/:traceId.
@@ -101,7 +101,7 @@ export type GetCloudWatchTraceHandler = (
   traceId: string,
   startTime?: number,
   endTime?: number
-) => Promise<{ success: boolean; records?: unknown[]; spans?: unknown[]; error?: string }>;
+) => Promise<{ success: boolean; records?: unknown[]; spans?: unknown[]; error?: string | Error }>;
 
 /**
  * Custom handler for GET /api/memory.
@@ -111,7 +111,7 @@ export type ListMemoryRecordsHandler = (
   memoryName: string,
   namespace: string,
   strategyId?: string
-) => Promise<{ success: boolean; records?: unknown[]; error?: string }>;
+) => Promise<{ success: boolean; records?: unknown[]; error?: string | Error }>;
 
 /**
  * Custom handler for POST /api/memory/search.
@@ -122,7 +122,7 @@ export type RetrieveMemoryRecordsHandler = (
   namespace: string,
   searchQuery: string,
   strategyId?: string
-) => Promise<{ success: boolean; records?: unknown[]; error?: string }>;
+) => Promise<{ success: boolean; records?: unknown[]; error?: string | Error }>;
 
 export interface WebUIOptions {
   /** Server mode identifier (currently only 'dev' is used) */
diff --git a/src/cli/operations/eval/__tests__/list-eval-runs.test.ts b/src/cli/operations/eval/__tests__/list-eval-runs.test.ts
index c9a71a8cf..4bcf69339 100644
--- a/src/cli/operations/eval/__tests__/list-eval-runs.test.ts
+++ b/src/cli/operations/eval/__tests__/list-eval-runs.test.ts
@@ -29,6 +29,7 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({});
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toHaveLength(2);
   });
 
@@ -43,7 +44,9 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({ agent: 'agent-a' });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toHaveLength(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.runs!.every(r => r.agent === 'agent-a')).toBe(true);
   });
 
@@ -58,6 +61,7 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({ limit: 2 });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toHaveLength(2);
   });
 
@@ -72,8 +76,11 @@ describe('handleListEvalRuns', () => {
 
     const result = handleListEvalRuns({ agent: 'a', limit: 2 });
 
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toHaveLength(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.runs![0]!.timestamp).toBe('2025-01-15T10:00:00.000Z');
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.runs![1]!.timestamp).toBe('2025-01-15T12:00:00.000Z');
   });
 
@@ -83,6 +90,7 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({});
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toEqual([]);
   });
 
@@ -94,7 +102,9 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('disk error');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('disk error');
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.runs).toBeUndefined();
   });
 
@@ -106,6 +116,7 @@ describe('handleListEvalRuns', () => {
     const result = handleListEvalRuns({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('42');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('42');
   });
 });
diff --git a/src/cli/operations/eval/__tests__/logs-eval.test.ts b/src/cli/operations/eval/__tests__/logs-eval.test.ts
index 5411d842e..69b5adbb6 100644
--- a/src/cli/operations/eval/__tests__/logs-eval.test.ts
+++ b/src/cli/operations/eval/__tests__/logs-eval.test.ts
@@ -96,12 +96,13 @@ describe('handleLogsEval', () => {
 
   it('returns error when agent resolution fails', async () => {
     mockLoadDeployedProjectConfig.mockResolvedValue({});
-    mockResolveAgent.mockReturnValue({ success: false, error: 'No agents defined' });
+    mockResolveAgent.mockReturnValue({ success: false, error: new Error('No agents defined') });
 
     const result = await handleLogsEval({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('No agents defined');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('No agents defined');
   });
 
   it('returns error when no online eval configs exist for the agent', async () => {
@@ -112,7 +113,8 @@ describe('handleLogsEval', () => {
     const result = await handleLogsEval({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No deployed online eval configs found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No deployed online eval configs found');
   });
 
   it('returns error when online eval configs exist but none are deployed', async () => {
@@ -123,7 +125,8 @@ describe('handleLogsEval', () => {
     const result = await handleLogsEval({});
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No deployed online eval configs found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No deployed online eval configs found');
   });
 
   it('searches logs with time range when --since is specified', async () => {
diff --git a/src/cli/operations/eval/__tests__/pause-resume.test.ts b/src/cli/operations/eval/__tests__/pause-resume.test.ts
index 834525675..ee31bc1b9 100644
--- a/src/cli/operations/eval/__tests__/pause-resume.test.ts
+++ b/src/cli/operations/eval/__tests__/pause-resume.test.ts
@@ -47,6 +47,7 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'my-config' }, 'pause');
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.executionStatus).toBe('DISABLED');
     expect(mockUpdateOnlineEvalExecutionStatus).toHaveBeenCalledWith({
       region: 'us-east-1',
@@ -66,6 +67,7 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'my-config' }, 'resume');
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.executionStatus).toBe('ENABLED');
     expect(mockUpdateOnlineEvalExecutionStatus).toHaveBeenCalledWith({
       region: 'us-east-1',
@@ -84,7 +86,8 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'my-config' }, 'pause');
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No deployed targets found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No deployed targets found');
   });
 
   it('returns error when config name is not found in deployed state', async () => {
@@ -93,8 +96,10 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'missing-config' }, 'pause');
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('missing-config');
-    expect(result.error).toContain('not found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('missing-config');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not found');
   });
 
   it('returns error when target config is missing from aws-targets', async () => {
@@ -106,8 +111,10 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'my-config' }, 'pause');
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Target config');
-    expect(result.error).toContain('not found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Target config');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not found');
   });
 
   it('returns error when the SDK call fails', async () => {
@@ -117,7 +124,8 @@ describe('handlePauseResume', () => {
     const result = await handlePauseResume({ name: 'my-config' }, 'pause');
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('Service unavailable');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('Service unavailable');
   });
 
   describe('ARN mode', () => {
@@ -132,6 +140,7 @@ describe('handlePauseResume', () => {
       const result = await handlePauseResume({ name: '', arn }, 'pause');
 
       expect(result.success).toBe(true);
+      // @ts-expect-error -- test accesses success-branch field
       expect(result.executionStatus).toBe('DISABLED');
       expect(mockLoadDeployedProjectConfig).not.toHaveBeenCalled();
       expect(mockUpdateOnlineEvalExecutionStatus).toHaveBeenCalledWith({
@@ -152,6 +161,7 @@ describe('handlePauseResume', () => {
       const result = await handlePauseResume({ name: '', arn, region: 'eu-west-1' }, 'resume');
 
       expect(result.success).toBe(true);
+      // @ts-expect-error -- test accesses success-branch field
       expect(result.executionStatus).toBe('ENABLED');
       expect(mockUpdateOnlineEvalExecutionStatus).toHaveBeenCalledWith({
         region: 'eu-west-1',
@@ -164,7 +174,8 @@ describe('handlePauseResume', () => {
       const result = await handlePauseResume({ name: '', arn: 'not-an-arn' }, 'pause');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Invalid online eval config ARN');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Invalid online eval config ARN');
     });
 
     it('returns error when config ID cannot be extracted from ARN', async () => {
@@ -172,7 +183,8 @@ describe('handlePauseResume', () => {
       const result = await handlePauseResume({ name: '', arn }, 'pause');
 
       expect(result.success).toBe(false);
-      expect(result.error).toContain('Could not extract config ID');
+      // @ts-expect-error -- test accesses failure-branch field
+      expect(result.error.message).toContain('Could not extract config ID');
     });
   });
 });
diff --git a/src/cli/operations/eval/__tests__/run-eval.test.ts b/src/cli/operations/eval/__tests__/run-eval.test.ts
index 39314af69..0d8edcf30 100644
--- a/src/cli/operations/eval/__tests__/run-eval.test.ts
+++ b/src/cli/operations/eval/__tests__/run-eval.test.ts
@@ -146,12 +146,13 @@ describe('handleRunEval', () => {
 
   it('returns error when agent resolution fails', async () => {
     mockLoadDeployedProjectConfig.mockResolvedValue({});
-    mockResolveAgent.mockReturnValue({ success: false, error: 'No agents defined' });
+    mockResolveAgent.mockReturnValue({ success: false, error: new Error('No agents defined') });
 
     const result = await handleRunEval({ evaluator: ['Builtin.GoalSuccessRate'], days: 7 });
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('No agents defined');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('No agents defined');
   });
 
   it('returns error when a custom evaluator is not found in deployed state', async () => {
@@ -171,8 +172,10 @@ describe('handleRunEval', () => {
     const result = await handleRunEval({ evaluator: ['MissingEval'], days: 7 });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('MissingEval');
-    expect(result.error).toContain('not found in deployed state');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('MissingEval');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not found in deployed state');
   });
 
   it('resolves builtin evaluators without deployed state lookup', async () => {
@@ -195,7 +198,8 @@ describe('handleRunEval', () => {
     const result = await handleRunEval({ evaluator: ['Builtin.GoalSuccessRate'], days: 7 });
 
     // Fails because no spans, but NOT because evaluator wasn't found
-    expect(result.error).toContain('No session spans found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No session spans found');
   });
 
   it('resolves custom evaluator name to deployed evaluator ID', async () => {
@@ -279,8 +283,10 @@ describe('handleRunEval', () => {
     const result = await handleRunEval({ evaluator: ['Builtin.GoalSuccessRate'], days: 7 });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No session spans found');
-    expect(result.error).toContain('my-agent');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No session spans found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('my-agent');
   });
 
   // ─── Successful evaluation ────────────────────────────────────────────────
@@ -325,10 +331,14 @@ describe('handleRunEval', () => {
     const result = await handleRunEval({ evaluator: ['Builtin.GoalSuccessRate'], days: 7 });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.run).toBeDefined();
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.sessionCount).toBe(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results).toHaveLength(1);
 
+    // @ts-expect-error -- test accesses discriminated union field
     const evalResult = result.run!.results[0]!;
     expect(evalResult.aggregateScore).toBe(3.0); // (4 + 2) / 2
     expect(evalResult.sessionScores).toHaveLength(2);
@@ -362,6 +372,7 @@ describe('handleRunEval', () => {
     const result = await handleRunEval({ evaluator: ['Builtin.GoalSuccessRate'], days: 7 });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     const evalResult = result.run!.results[0]!;
     // Only the non-errored session (value 5.0) should be in the aggregate
     expect(evalResult.aggregateScore).toBe(5.0);
@@ -394,6 +405,7 @@ describe('handleRunEval', () => {
     expect(result.success).toBe(true);
     expect(mockSaveEvalRun).toHaveBeenCalled();
     expect(mockWriteFileSync).not.toHaveBeenCalled();
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.filePath).toBe('/tmp/eval-results/eval_2025-01-15_10-00-00.json');
   });
 
@@ -425,6 +437,7 @@ describe('handleRunEval', () => {
     expect(result.success).toBe(true);
     expect(mockWriteFileSync).toHaveBeenCalledWith('/tmp/my-output.json', expect.any(String));
     expect(mockSaveEvalRun).not.toHaveBeenCalled();
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.filePath).toBe('/tmp/my-output.json');
   });
 
@@ -462,10 +475,15 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results).toHaveLength(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results[0]!.evaluator).toBe('Builtin.GoalSuccessRate');
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results[0]!.aggregateScore).toBe(0.9);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results[1]!.evaluator).toBe('CustomEval');
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.results[1]!.aggregateScore).toBe(4.5);
   });
 
@@ -485,6 +503,7 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.agent).toBe('rt-arn-test');
     expect(mockLoadDeployedProjectConfig).not.toHaveBeenCalled();
     expect(mockResolveAgent).not.toHaveBeenCalled();
@@ -533,7 +552,8 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Invalid agent runtime ARN');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Invalid agent runtime ARN');
   });
 
   it('rejects custom evaluator names in ARN mode', async () => {
@@ -544,7 +564,8 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('cannot be resolved in ARN mode');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('cannot be resolved in ARN mode');
   });
 
   it('saves to cwd in ARN mode when no --output is specified', async () => {
@@ -566,6 +587,7 @@ describe('handleRunEval', () => {
       expect.stringContaining('eval_2025-01-15_10-00-00.json'),
       expect.any(String)
     );
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.filePath).toContain('eval_2025-01-15_10-00-00.json');
   });
 
@@ -584,6 +606,7 @@ describe('handleRunEval', () => {
 
     expect(result.success).toBe(true);
     expect(mockWriteFileSync).toHaveBeenCalledWith('/tmp/custom-eval.json', expect.any(String));
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.filePath).toBe('/tmp/custom-eval.json');
   });
 
@@ -595,7 +618,8 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No evaluators specified');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No evaluators specified');
   });
 
   // ─── Endpoint selection ──────────────────────────────────────────────────
@@ -1200,6 +1224,7 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.run!.referenceInputs).toEqual({
       expectedTrajectory: ['tool_1', 'tool_2'],
     });
@@ -1216,6 +1241,7 @@ describe('handleRunEval', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('require exactly one session');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('require exactly one session');
   });
 });
diff --git a/src/cli/operations/eval/batch-eval-storage.ts b/src/cli/operations/eval/batch-eval-storage.ts
index 3145120ba..7296c8aaa 100644
--- a/src/cli/operations/eval/batch-eval-storage.ts
+++ b/src/cli/operations/eval/batch-eval-storage.ts
@@ -40,7 +40,7 @@ export function saveBatchEvalRun(result: RunBatchEvaluationCommandResult): strin
     completedAt: result.completedAt,
     evaluators: result.results.map(r => r.evaluatorId),
     results: result.results,
-    evaluationResults: result.evaluationResults,
+    evaluationResults: result.success ? result.evaluationResults : undefined,
   };
 
   writeFileSync(filePath, JSON.stringify(record, null, 2));
diff --git a/src/cli/operations/eval/list-eval-runs.ts b/src/cli/operations/eval/list-eval-runs.ts
index 66b0ed528..96674a0c8 100644
--- a/src/cli/operations/eval/list-eval-runs.ts
+++ b/src/cli/operations/eval/list-eval-runs.ts
@@ -1,12 +1,9 @@
+import type { Result } from '../../../lib/types';
 import { getErrorMessage } from '../../errors';
 import { listEvalRuns } from './storage';
 import type { EvalRunResult, ListEvalRunsOptions } from './types';
 
-export interface ListEvalRunsResult {
-  success: boolean;
-  error?: string;
-  runs?: EvalRunResult[];
-}
+export type ListEvalRunsResult = Result<{ runs: EvalRunResult[] }>;
 
 export function handleListEvalRuns(options: ListEvalRunsOptions): ListEvalRunsResult {
   try {
@@ -22,6 +19,6 @@ export function handleListEvalRuns(options: ListEvalRunsOptions): ListEvalRunsRe
 
     return { success: true, runs };
   } catch (err) {
-    return { success: false, error: getErrorMessage(err) };
+    return { success: false, error: new Error(getErrorMessage(err)) };
   }
 }
diff --git a/src/cli/operations/eval/logs-eval.ts b/src/cli/operations/eval/logs-eval.ts
index 430103a44..070993a3e 100644
--- a/src/cli/operations/eval/logs-eval.ts
+++ b/src/cli/operations/eval/logs-eval.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { parseTimeString } from '../../../lib/utils';
 import { getOnlineEvaluationConfig } from '../../aws/agentcore-control';
 import { searchLogs, streamLogs } from '../../aws/cloudwatch';
@@ -13,10 +14,7 @@ export interface LogsEvalOptions {
   follow?: boolean;
 }
 
-export interface LogsEvalResult {
-  success: boolean;
-  error?: string;
-}
+export type LogsEvalResult = Result;
 
 function formatLogLine(event: { timestamp: number; message: string }, json: boolean): string {
   if (json) {
@@ -75,7 +73,7 @@ export async function handleLogsEval(options: LogsEvalOptions): Promise<LogsEval
   const agentResult = resolveAgent(context, { runtime: options.agent });
 
   if (!agentResult.success) {
-    return { success: false, error: agentResult.error };
+    return { success: false, error: new Error(agentResult.error.message) };
   }
 
   const { agent } = agentResult;
@@ -85,7 +83,7 @@ export async function handleLogsEval(options: LogsEvalOptions): Promise<LogsEval
   if (resolvedLogGroups.length === 0) {
     return {
       success: false,
-      error: `No deployed online eval configs found. Add one with 'agentcore add online-eval' and deploy.`,
+      error: new Error(`No deployed online eval configs found. Add one with 'agentcore add online-eval' and deploy.`),
     };
   }
 
diff --git a/src/cli/operations/eval/pause-resume.ts b/src/cli/operations/eval/pause-resume.ts
index ce2ff467b..b773705b1 100644
--- a/src/cli/operations/eval/pause-resume.ts
+++ b/src/cli/operations/eval/pause-resume.ts
@@ -1,23 +1,17 @@
+import type { Result } from '../../../lib/types';
 import type { OnlineEvalExecutionStatus } from '../../aws/agentcore-control';
 import { updateOnlineEvalExecutionStatus } from '../../aws/agentcore-control';
 import { loadDeployedProjectConfig } from '../resolve-agent';
 import type { OnlineEvalActionOptions } from './types';
 
-export interface PauseResumeResult {
-  success: boolean;
-  error?: string;
-  configId?: string;
-  executionStatus?: string;
-}
+export type PauseResumeResult = Result<{ configId: string; executionStatus: string }>;
 
-async function resolveOnlineEvalConfig(
-  configName: string
-): Promise<{ success: true; configId: string; region: string } | { success: false; error: string }> {
+async function resolveOnlineEvalConfig(configName: string): Promise<Result<{ configId: string; region: string }>> {
   const context = await loadDeployedProjectConfig();
   const targetNames = Object.keys(context.deployedState.targets);
 
   if (targetNames.length === 0) {
-    return { success: false, error: 'No deployed targets found. Run `agentcore deploy` first.' };
+    return { success: false, error: new Error('No deployed targets found. Run `agentcore deploy` first.') };
   }
 
   const targetName = targetNames[0]!;
@@ -27,13 +21,13 @@ async function resolveOnlineEvalConfig(
   if (!deployedConfig) {
     return {
       success: false,
-      error: `Online eval config "${configName}" not found in deployed state. Has it been deployed?`,
+      error: new Error(`Online eval config "${configName}" not found in deployed state. Has it been deployed?`),
     };
   }
 
   const targetConfig = context.awsTargets.find(t => t.name === targetName);
   if (!targetConfig) {
-    return { success: false, error: `Target config "${targetName}" not found in aws-targets.` };
+    return { success: false, error: new Error(`Target config "${targetName}" not found in aws-targets.`) };
   }
 
   return {
@@ -47,24 +41,21 @@ async function resolveOnlineEvalConfig(
  * Parse an online eval config ARN to extract the config ID and region.
  * ARN format: arn:aws:bedrock-agentcore:<region>:<account>:online-evaluation-config/<configId>
  */
-function parseOnlineEvalConfigArn(
-  arn: string,
-  regionOverride?: string
-): { success: true; configId: string; region: string } | { success: false; error: string } {
+function parseOnlineEvalConfigArn(arn: string, regionOverride?: string): Result<{ configId: string; region: string }> {
   const parts = arn.split(':');
   if (parts.length < 6 || !arn.startsWith('arn:')) {
-    return { success: false, error: `Invalid online eval config ARN: ${arn}` };
+    return { success: false, error: new Error(`Invalid online eval config ARN: ${arn}`) };
   }
 
   const region = regionOverride ?? parts[3];
   if (!region) {
-    return { success: false, error: 'Could not determine region from ARN. Use --region to specify.' };
+    return { success: false, error: new Error('Could not determine region from ARN. Use --region to specify.') };
   }
 
   const resource = parts.slice(5).join(':');
   const match = /online-evaluation-config\/(.+)$/.exec(resource);
   if (!match) {
-    return { success: false, error: `Could not extract config ID from ARN: ${arn}` };
+    return { success: false, error: new Error(`Could not extract config ID from ARN: ${arn}`) };
   }
 
   return { success: true, configId: match[1]!, region };
@@ -73,9 +64,7 @@ function parseOnlineEvalConfigArn(
 /**
  * Resolve config ID and region from either a project config name or an ARN.
  */
-async function resolveConfig(
-  options: OnlineEvalActionOptions
-): Promise<{ success: true; configId: string; region: string } | { success: false; error: string }> {
+async function resolveConfig(options: OnlineEvalActionOptions): Promise<Result<{ configId: string; region: string }>> {
   if (options.arn) {
     return parseOnlineEvalConfigArn(options.arn, options.region);
   }
@@ -88,7 +77,7 @@ export async function handlePauseResume(
 ): Promise<PauseResumeResult> {
   const resolution = await resolveConfig(options);
   if (!resolution.success) {
-    return resolution;
+    return { success: false, error: new Error(resolution.error.message) };
   }
 
   const executionStatus: OnlineEvalExecutionStatus = action === 'pause' ? 'DISABLED' : 'ENABLED';
@@ -106,6 +95,6 @@ export async function handlePauseResume(
       executionStatus: result.executionStatus,
     };
   } catch (err) {
-    return { success: false, error: (err as Error).message };
+    return { success: false, error: err instanceof Error ? err : new Error(String(err)) };
   }
 }
diff --git a/src/cli/operations/eval/run-batch-evaluation.ts b/src/cli/operations/eval/run-batch-evaluation.ts
index 0962f4e0a..2cc595bb6 100644
--- a/src/cli/operations/eval/run-batch-evaluation.ts
+++ b/src/cli/operations/eval/run-batch-evaluation.ts
@@ -7,6 +7,7 @@
  *   5. Return results
  */
 import { ConfigIO } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import type { DeployedState } from '../../../schema';
 import { generateClientToken, getBatchEvaluation, startBatchEvaluation } from '../../aws/agentcore-batch-evaluation';
 import type {
@@ -54,18 +55,17 @@ export interface BatchEvaluationResult {
   error?: string;
 }
 
-export interface RunBatchEvaluationCommandResult {
-  success: boolean;
-  error?: string;
+export type RunBatchEvaluationCommandResult = Result<{
+  evaluationResults?: EvaluationResults;
+}> & {
   batchEvaluationId?: string;
   name?: string;
   status?: string;
   results: BatchEvaluationResult[];
-  evaluationResults?: EvaluationResults;
   startedAt?: string;
   completedAt?: string;
   logFilePath?: string;
-}
+};
 
 // ============================================================================
 // Constants
@@ -116,7 +116,7 @@ export async function runBatchEvaluationCommand(
       logger?.log(error, 'error');
       logger?.endStep('error', error);
       logger?.finalize(false);
-      return { success: false, error, results: [], logFilePath: logger?.logFilePath };
+      return { success: false, error: new Error(error), results: [], logFilePath: logger?.logFilePath };
     }
 
     const runtimeId = agentState.runtimeId;
@@ -152,7 +152,9 @@ export async function runBatchEvaluationCommand(
       if (!/^[a-zA-Z][a-zA-Z0-9_]{0,47}$/.test(options.name)) {
         return {
           success: false,
-          error: `Batch evaluation name must start with a letter and contain only letters, digits, and underscores (max 48 chars). Got: "${options.name}"`,
+          error: new Error(
+            `Batch evaluation name must start with a letter and contain only letters, digits, and underscores (max 48 chars). Got: "${options.name}"`
+          ),
           results: [],
           logFilePath: logger?.logFilePath,
         };
@@ -242,7 +244,7 @@ export async function runBatchEvaluationCommand(
       logger?.finalize(false);
       return {
         success: false,
-        error,
+        error: new Error(error),
         batchEvaluationId: startResult.batchEvaluationId,
         name: evalName,
         status: current.status,
@@ -287,7 +289,12 @@ export async function runBatchEvaluationCommand(
     const error = err instanceof Error ? err.message : String(err);
     logger?.log(error, 'error');
     logger?.finalize(false);
-    return { success: false, error, results: [], logFilePath: logger?.logFilePath };
+    return {
+      success: false,
+      error: err instanceof Error ? err : new Error(error),
+      results: [],
+      logFilePath: logger?.logFilePath,
+    };
   }
 }
 
diff --git a/src/cli/operations/eval/run-eval.ts b/src/cli/operations/eval/run-eval.ts
index 90cd519c7..393068d9d 100644
--- a/src/cli/operations/eval/run-eval.ts
+++ b/src/cli/operations/eval/run-eval.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws';
 import { evaluate } from '../../aws/agentcore';
 import type { EvaluationReferenceInput } from '../../aws/agentcore';
@@ -30,7 +31,7 @@ interface ResolvedEvalContext {
   evaluatorLabels: string[];
 }
 
-type ResolveResult = { success: true; ctx: ResolvedEvalContext } | { success: false; error: string };
+type ResolveResult = Result<{ ctx: ResolvedEvalContext }>;
 
 /**
  * Resolve evaluator IDs from ARN strings or raw IDs.
@@ -53,18 +54,18 @@ function resolveFromArn(options: RunEvalOptions): ResolveResult {
   // Parse ARN: arn:aws:bedrock-agentcore:<region>:<account>:runtime/<runtimeId>
   const arnParts = arn.split(':');
   if (arnParts.length < 6) {
-    return { success: false, error: `Invalid agent runtime ARN: ${arn}` };
+    return { success: false, error: new Error(`Invalid agent runtime ARN: ${arn}`) };
   }
 
   const region = options.region ?? arnParts[3];
   if (!region) {
-    return { success: false, error: 'Could not determine region from ARN. Use --region to specify.' };
+    return { success: false, error: new Error('Could not determine region from ARN. Use --region to specify.') };
   }
 
   const resourcePart = arnParts.slice(5).join(':');
   const runtimeMatch = /runtime\/(.+)$/.exec(resourcePart);
   if (!runtimeMatch) {
-    return { success: false, error: `Could not extract runtime ID from ARN: ${arn}` };
+    return { success: false, error: new Error(`Could not extract runtime ID from ARN: ${arn}`) };
   }
   const runtimeId = runtimeMatch[1]!;
 
@@ -79,7 +80,9 @@ function resolveFromArn(options: RunEvalOptions): ResolveResult {
     } else {
       return {
         success: false,
-        error: `Custom evaluator "${evalName}" cannot be resolved in ARN mode. Use --evaluator-arn with an evaluator ARN or ID, or use Builtin.* evaluators.`,
+        error: new Error(
+          `Custom evaluator "${evalName}" cannot be resolved in ARN mode. Use --evaluator-arn with an evaluator ARN or ID, or use Builtin.* evaluators.`
+        ),
       };
     }
   }
@@ -91,7 +94,10 @@ function resolveFromArn(options: RunEvalOptions): ResolveResult {
   }
 
   if (evaluatorIds.length === 0) {
-    return { success: false, error: 'No evaluators specified. Use -e/--evaluator with Builtin.* or --evaluator-arn.' };
+    return {
+      success: false,
+      error: new Error('No evaluators specified. Use -e/--evaluator with Builtin.* or --evaluator-arn.'),
+    };
   }
 
   const endpointName = options.endpoint ?? process.env.AGENTCORE_RUNTIME_ENDPOINT ?? DEFAULT_ENDPOINT_NAME;
@@ -139,7 +145,7 @@ function resolveFromProject(context: DeployedProjectConfig, options: RunEvalOpti
     if (!deployedEval) {
       return {
         success: false,
-        error: `Evaluator "${evalName}" not found in deployed state. Has it been deployed?`,
+        error: new Error(`Evaluator "${evalName}" not found in deployed state. Has it been deployed?`),
       };
     }
     evaluatorIds.push(deployedEval.evaluatorId);
@@ -154,7 +160,7 @@ function resolveFromProject(context: DeployedProjectConfig, options: RunEvalOpti
   }
 
   if (evaluatorIds.length === 0) {
-    return { success: false, error: 'No evaluators specified. Use -e/--evaluator or --evaluator-arn.' };
+    return { success: false, error: new Error('No evaluators specified. Use -e/--evaluator or --evaluator-arn.') };
   }
 
   return {
@@ -551,12 +557,7 @@ async function fetchSessionSpans(opts: FetchSpansOptions): Promise<SessionSpans[
   return sessions;
 }
 
-export interface RunEvalResult {
-  success: boolean;
-  error?: string;
-  run?: EvalRunResult;
-  filePath?: string;
-}
+export type RunEvalResult = Result<{ run: EvalRunResult; filePath: string }>;
 
 export async function handleRunEval(options: RunEvalOptions): Promise<RunEvalResult> {
   let resolution: ResolveResult;
@@ -569,7 +570,7 @@ export async function handleRunEval(options: RunEvalOptions): Promise<RunEvalRes
   }
 
   if (!resolution.success) {
-    return { success: false, error: resolution.error };
+    return { success: false, error: new Error(resolution.error.message) };
   }
 
   const { ctx } = resolution;
@@ -593,7 +594,9 @@ export async function handleRunEval(options: RunEvalOptions): Promise<RunEvalRes
   if (sessions.length === 0) {
     return {
       success: false,
-      error: `No session spans found for agent "${ctx.agentLabel}" in the last ${options.days} day(s). Has the agent been invoked?`,
+      error: new Error(
+        `No session spans found for agent "${ctx.agentLabel}" in the last ${options.days} day(s). Has the agent been invoked?`
+      ),
     };
   }
 
@@ -610,8 +613,9 @@ export async function handleRunEval(options: RunEvalOptions): Promise<RunEvalRes
   if (hasRefInputs && sessions.length !== 1) {
     return {
       success: false,
-      error:
-        'Ground truth flags (-A, --expected-trajectory, --expected-response) require exactly one session. Use -s/--session-id to target a single session.',
+      error: new Error(
+        'Ground truth flags (-A, --expected-trajectory, --expected-response) require exactly one session. Use -s/--session-id to target a single session.'
+      ),
     };
   }
   if (hasRefInputs) {
@@ -642,7 +646,9 @@ export async function handleRunEval(options: RunEvalOptions): Promise<RunEvalRes
       if (!traceId) {
         return {
           success: false,
-          error: 'Expected response provided but no trace IDs found in session spans. Use -t/--trace-id to specify.',
+          error: new Error(
+            'Expected response provided but no trace IDs found in session spans. Use -t/--trace-id to specify.'
+          ),
         };
       }
       refInputs.push({
diff --git a/src/cli/operations/mcp/__tests__/create-mcp-utils.test.ts b/src/cli/operations/mcp/__tests__/create-mcp-utils.test.ts
index 19cb635a1..45dfc1169 100644
--- a/src/cli/operations/mcp/__tests__/create-mcp-utils.test.ts
+++ b/src/cli/operations/mcp/__tests__/create-mcp-utils.test.ts
@@ -200,7 +200,10 @@ describe('GatewayPrimitive.add (createGateway)', () => {
     });
 
     expect(result).toEqual(
-      expect.objectContaining({ success: false, error: expect.stringContaining('Gateway "dup-gw" already exists') })
+      expect.objectContaining({
+        success: false,
+        error: expect.objectContaining({ message: expect.stringContaining('Gateway "dup-gw" already exists') }),
+      })
     );
   });
 
diff --git a/src/cli/operations/memory/__tests__/create-memory.test.ts b/src/cli/operations/memory/__tests__/create-memory.test.ts
index a0b8077c4..09c827ac0 100644
--- a/src/cli/operations/memory/__tests__/create-memory.test.ts
+++ b/src/cli/operations/memory/__tests__/create-memory.test.ts
@@ -86,7 +86,7 @@ describe('add', () => {
       expiry: 30,
     });
 
-    expect(result).toEqual(expect.objectContaining({ success: false, error: expect.any(String) }));
+    expect(result).toEqual(expect.objectContaining({ success: false, error: expect.any(Error) }));
     expect(mockWriteProjectSpec).not.toHaveBeenCalled();
   });
 
@@ -96,7 +96,10 @@ describe('add', () => {
     const result = await primitive.add({ name: 'Existing', strategies: '', expiry: 30 });
 
     expect(result).toEqual(
-      expect.objectContaining({ success: false, error: expect.stringContaining('Memory "Existing" already exists') })
+      expect.objectContaining({
+        success: false,
+        error: expect.objectContaining({ message: expect.stringContaining('Memory "Existing" already exists') }),
+      })
     );
   });
 });
diff --git a/src/cli/operations/memory/list-memory-records.ts b/src/cli/operations/memory/list-memory-records.ts
index 8bbf34628..b31b077d6 100644
--- a/src/cli/operations/memory/list-memory-records.ts
+++ b/src/cli/operations/memory/list-memory-records.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws';
 import { BedrockAgentCoreClient, ListMemoryRecordsCommand } from '@aws-sdk/client-bedrock-agentcore';
 
@@ -20,12 +21,7 @@ export interface ListMemoryRecordsOptions {
   nextToken?: string;
 }
 
-export interface ListMemoryRecordsResult {
-  success: boolean;
-  records?: MemoryRecordEntry[];
-  nextToken?: string;
-  error?: string;
-}
+export type ListMemoryRecordsResult = Result<{ records: MemoryRecordEntry[]; nextToken?: string }>;
 
 /**
  * Lists memory records for a deployed memory resource via the AWS SDK.
@@ -63,8 +59,8 @@ export async function listMemoryRecords(options: ListMemoryRecordsOptions): Prom
   } catch (error: unknown) {
     const err = error as Error;
     if (err.name === 'ResourceNotFoundException') {
-      return { success: false, error: `Memory '${memoryId}' not found. It may not have been deployed yet.` };
+      return { success: false, error: new Error(`Memory '${memoryId}' not found. It may not have been deployed yet.`) };
     }
-    return { success: false, error: err.message ?? String(error) };
+    return { success: false, error: new Error(err.message ?? String(error)) };
   }
 }
diff --git a/src/cli/operations/memory/retrieve-memory-records.ts b/src/cli/operations/memory/retrieve-memory-records.ts
index e8d2a65ed..d2414ef25 100644
--- a/src/cli/operations/memory/retrieve-memory-records.ts
+++ b/src/cli/operations/memory/retrieve-memory-records.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws';
 import type { MemoryRecordEntry } from './list-memory-records';
 import { BedrockAgentCoreClient, RetrieveMemoryRecordsCommand } from '@aws-sdk/client-bedrock-agentcore';
@@ -13,12 +14,7 @@ export interface RetrieveMemoryRecordsOptions {
   nextToken?: string;
 }
 
-export interface RetrieveMemoryRecordsResult {
-  success: boolean;
-  records?: MemoryRecordEntry[];
-  nextToken?: string;
-  error?: string;
-}
+export type RetrieveMemoryRecordsResult = Result<{ records: MemoryRecordEntry[]; nextToken?: string }>;
 
 /**
  * Searches memory records using semantic retrieval via the AWS SDK.
@@ -62,8 +58,8 @@ export async function retrieveMemoryRecords(
   } catch (error: unknown) {
     const err = error as Error;
     if (err.name === 'ResourceNotFoundException') {
-      return { success: false, error: `Memory '${memoryId}' not found. It may not have been deployed yet.` };
+      return { success: false, error: new Error(`Memory '${memoryId}' not found. It may not have been deployed yet.`) };
     }
-    return { success: false, error: err.message ?? String(error) };
+    return { success: false, error: new Error(err.message ?? String(error)) };
   }
 }
diff --git a/src/cli/operations/recommendation/__tests__/apply-to-bundle.test.ts b/src/cli/operations/recommendation/__tests__/apply-to-bundle.test.ts
index 5e0fb668a..686d5daed 100644
--- a/src/cli/operations/recommendation/__tests__/apply-to-bundle.test.ts
+++ b/src/cli/operations/recommendation/__tests__/apply-to-bundle.test.ts
@@ -99,6 +99,7 @@ describe('applyRecommendationToBundle', () => {
     );
 
     expect(applyResult.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(applyResult.newVersionId).toBe(NEW_VERSION_ID);
 
     // Verify spec was written with server components
@@ -133,6 +134,7 @@ describe('applyRecommendationToBundle', () => {
     );
 
     expect(applyResult.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(applyResult.newVersionId).toBe(NEW_VERSION_ID);
   });
 
@@ -153,6 +155,7 @@ describe('applyRecommendationToBundle', () => {
     );
 
     expect(applyResult.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(applyResult.newVersionId).toBe(NEW_VERSION_ID);
   });
 
@@ -172,7 +175,8 @@ describe('applyRecommendationToBundle', () => {
     );
 
     expect(applyResult.success).toBe(false);
-    expect(applyResult.error).toContain('does not contain a new config bundle version');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(applyResult.error.message).toContain('does not contain a new config bundle version');
     expect(writeSpecSpy).not.toHaveBeenCalled();
   });
 
@@ -193,7 +197,8 @@ describe('applyRecommendationToBundle', () => {
     );
 
     expect(applyResult.success).toBe(false);
-    expect(applyResult.error).toContain('NonExistent');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(applyResult.error.message).toContain('NonExistent');
     expect(writeSpecSpy).not.toHaveBeenCalled();
   });
 });
diff --git a/src/cli/operations/recommendation/__tests__/recommendation-storage.test.ts b/src/cli/operations/recommendation/__tests__/recommendation-storage.test.ts
index f6a60b6e8..1ff0f4c55 100644
--- a/src/cli/operations/recommendation/__tests__/recommendation-storage.test.ts
+++ b/src/cli/operations/recommendation/__tests__/recommendation-storage.test.ts
@@ -17,9 +17,9 @@ function makeTmpDir(): string {
   return dir;
 }
 
-function makeResult(overrides: Partial<RunRecommendationCommandResult> = {}): RunRecommendationCommandResult {
+function makeResult(overrides: Record<string, unknown> = {}): RunRecommendationCommandResult {
   return {
-    success: true,
+    success: true as const,
     recommendationId: 'rec-123',
     status: 'COMPLETED',
     startedAt: '2026-03-24T10:00:00.000Z',
diff --git a/src/cli/operations/recommendation/__tests__/run-recommendation.test.ts b/src/cli/operations/recommendation/__tests__/run-recommendation.test.ts
index b26a59b32..7e7dfab9a 100644
--- a/src/cli/operations/recommendation/__tests__/run-recommendation.test.ts
+++ b/src/cli/operations/recommendation/__tests__/run-recommendation.test.ts
@@ -72,8 +72,10 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('NonExistentAgent');
-    expect(result.error).toContain('not deployed');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('NonExistentAgent');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not deployed');
   });
 
   it('returns error when evaluator cannot be resolved', async () => {
@@ -87,8 +89,10 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('UnknownEvaluator');
-    expect(result.error).toContain('not found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('UnknownEvaluator');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not found');
   });
 
   it('returns result on COMPLETED status', async () => {
@@ -126,6 +130,7 @@ describe('runRecommendationCommand', () => {
     expect(result.success).toBe(true);
     expect(result.recommendationId).toBe('rec-001');
     expect(result.status).toBe('COMPLETED');
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.result?.systemPromptRecommendationResult?.recommendedSystemPrompt).toBe('Optimized prompt');
   });
 
@@ -154,7 +159,8 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('FAILED');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('FAILED');
     expect(result.recommendationId).toBe('rec-002');
   });
 
@@ -288,7 +294,8 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('API timeout');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('API timeout');
   });
 
   it('retries transient poll failures and succeeds', async () => {
@@ -346,9 +353,12 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('consecutive errors');
-    expect(result.error).toContain('fetch failed');
-    expect(result.error).toContain('rec-retry-fail');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('consecutive errors');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('fetch failed');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('rec-retry-fail');
     expect(mockGetRecommendation).toHaveBeenCalledTimes(3);
   });
 
@@ -378,8 +388,10 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Polling timed out');
-    expect(result.error).toContain('rec-timeout');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Polling timed out');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('rec-timeout');
   });
 
   it('reads system prompt from file when inputSource is file', async () => {
@@ -539,7 +551,8 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No spans found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No spans found');
   });
 
   it('derives service name from runtimeId by stripping hash suffix', async () => {
@@ -665,9 +678,12 @@ describe('runRecommendationCommand', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Insufficient trace data');
-    expect(result.error).toContain('INSUFFICIENT_DATA');
-    expect(result.error).toContain('Not enough traces');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Insufficient trace data');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('INSUFFICIENT_DATA');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Not enough traces');
     // Request IDs are logged to file only, not included in the error message
   });
 
diff --git a/src/cli/operations/recommendation/apply-to-bundle.ts b/src/cli/operations/recommendation/apply-to-bundle.ts
index bf9060d10..8ed55ff0d 100644
--- a/src/cli/operations/recommendation/apply-to-bundle.ts
+++ b/src/cli/operations/recommendation/apply-to-bundle.ts
@@ -10,6 +10,7 @@
  * updates the local agentcore.json components to match the server state.
  */
 import { ConfigIO } from '../../../lib';
+import type { Result } from '../../../lib/types';
 import { getConfigurationBundleVersion } from '../../aws/agentcore-config-bundles';
 import type { RecommendationResult } from '../../aws/agentcore-recommendation';
 
@@ -24,12 +25,7 @@ export interface ApplyRecommendationOptions {
   region: string;
 }
 
-export interface ApplyRecommendationResult {
-  success: boolean;
-  error?: string;
-  /** New version ID that was synced from the server */
-  newVersionId?: string;
-}
+export type ApplyRecommendationResult = Result<{ newVersionId: string }>;
 
 /**
  * Extract the bundleId from a bundle ARN.
@@ -58,8 +54,9 @@ export async function applyRecommendationToBundle(
   if (!resultBundle) {
     return {
       success: false,
-      error:
-        'Recommendation result does not contain a new config bundle version. The server may not have applied the recommendation to the bundle.',
+      error: new Error(
+        'Recommendation result does not contain a new config bundle version. The server may not have applied the recommendation to the bundle.'
+      ),
     };
   }
 
@@ -67,7 +64,7 @@ export async function applyRecommendationToBundle(
   if (!bundleId) {
     return {
       success: false,
-      error: `Could not extract bundle ID from ARN: ${resultBundle.bundleArn}`,
+      error: new Error(`Could not extract bundle ID from ARN: ${resultBundle.bundleArn}`),
     };
   }
 
@@ -107,7 +104,7 @@ export async function applyRecommendationToBundle(
   if (!bundle) {
     return {
       success: false,
-      error: `Config bundle "${identifier}" not found in agentcore.json.`,
+      error: new Error(`Config bundle "${identifier}" not found in agentcore.json.`),
     };
   }
 
diff --git a/src/cli/operations/recommendation/recommendation-storage.ts b/src/cli/operations/recommendation/recommendation-storage.ts
index e60846574..575a86ef9 100644
--- a/src/cli/operations/recommendation/recommendation-storage.ts
+++ b/src/cli/operations/recommendation/recommendation-storage.ts
@@ -45,7 +45,7 @@ export function saveRecommendationRun(
     status: result.status ?? 'unknown',
     startedAt: result.startedAt,
     completedAt: result.completedAt,
-    result: result.result,
+    result: result.success ? result.result : undefined,
   };
 
   writeFileSync(filePath, JSON.stringify(record, null, 2));
diff --git a/src/cli/operations/recommendation/run-recommendation.ts b/src/cli/operations/recommendation/run-recommendation.ts
index 0423cfe32..25ab9a1d3 100644
--- a/src/cli/operations/recommendation/run-recommendation.ts
+++ b/src/cli/operations/recommendation/run-recommendation.ts
@@ -60,7 +60,7 @@ export async function runRecommendationCommand(
       logger?.finalize(false);
       return {
         success: false,
-        error: `Agent "${options.agent}" not deployed. Run \`agentcore deploy\` first.`,
+        error: new Error(`Agent "${options.agent}" not deployed. Run \`agentcore deploy\` first.`),
         logFilePath: logger?.logFilePath,
       };
     }
@@ -73,7 +73,9 @@ export async function runRecommendationCommand(
       if (!evaluatorId) {
         return {
           success: false,
-          error: `Evaluator "${evaluator}" not found in deployed state. Use a Builtin.* name, a full ARN, or deploy a custom evaluator first.`,
+          error: new Error(
+            `Evaluator "${evaluator}" not found in deployed state. Use a Builtin.* name, a full ARN, or deploy a custom evaluator first.`
+          ),
           logFilePath: logger?.logFilePath,
         };
       }
@@ -82,7 +84,7 @@ export async function runRecommendationCommand(
     if (options.type === 'SYSTEM_PROMPT_RECOMMENDATION' && evaluatorIds.length !== 1) {
       return {
         success: false,
-        error: 'System prompt recommendations require exactly one evaluator.',
+        error: new Error('System prompt recommendations require exactly one evaluator.'),
         logFilePath: logger?.logFilePath,
       };
     }
@@ -105,7 +107,7 @@ export async function runRecommendationCommand(
     ) {
       return {
         success: false,
-        error: 'System prompt content is required. Provide via --inline, --prompt-file, or --bundle-name.',
+        error: new Error('System prompt content is required. Provide via --inline, --prompt-file, or --bundle-name.'),
         logFilePath: logger?.logFilePath,
       };
     }
@@ -132,7 +134,9 @@ export async function runRecommendationCommand(
         if (!bundleArn) {
           return {
             success: false,
-            error: `Config bundle "${options.bundleName}" not found in deployed state. Run \`agentcore deploy\` first.`,
+            error: new Error(
+              `Config bundle "${options.bundleName}" not found in deployed state. Run \`agentcore deploy\` first.`
+            ),
             logFilePath: logger?.logFilePath,
           };
         }
@@ -230,7 +234,9 @@ export async function runRecommendationCommand(
         logger?.finalize(false);
         return {
           success: false,
-          error: `Polling timed out after ${Math.round(maxDurationMs / 60000)} minutes. The recommendation may still be running server-side.\nRecommendation ID: ${startResult.recommendationId}`,
+          error: new Error(
+            `Polling timed out after ${Math.round(maxDurationMs / 60000)} minutes. The recommendation may still be running server-side.\nRecommendation ID: ${startResult.recommendationId}`
+          ),
           recommendationId: startResult.recommendationId,
           status: currentStatus,
           logFilePath: logger?.logFilePath,
@@ -255,7 +261,9 @@ export async function runRecommendationCommand(
           logger?.finalize(false);
           return {
             success: false,
-            error: `Polling failed after ${MAX_POLL_RETRIES} consecutive errors: ${pollErrMsg}\nThe recommendation may still be running server-side.\nRecommendation ID: ${startResult.recommendationId}`,
+            error: new Error(
+              `Polling failed after ${MAX_POLL_RETRIES} consecutive errors: ${pollErrMsg}\nThe recommendation may still be running server-side.\nRecommendation ID: ${startResult.recommendationId}`
+            ),
             recommendationId: startResult.recommendationId,
             status: currentStatus,
             logFilePath: logger?.logFilePath,
@@ -303,9 +311,11 @@ export async function runRecommendationCommand(
 
         return {
           success: false,
-          error: failureDetails
-            ? `Recommendation failed: ${failureDetails}`
-            : `Recommendation finished with status: ${currentStatus}`,
+          error: new Error(
+            failureDetails
+              ? `Recommendation failed: ${failureDetails}`
+              : `Recommendation finished with status: ${currentStatus}`
+          ),
           recommendationId: startResult.recommendationId,
           status: currentStatus,
           logFilePath: logger?.logFilePath,
@@ -319,7 +329,7 @@ export async function runRecommendationCommand(
     logger?.finalize(false);
     return {
       success: false,
-      error: `Recommendation ended with unexpected status: ${currentStatus}`,
+      error: new Error(`Recommendation ended with unexpected status: ${currentStatus}`),
       recommendationId: startResult.recommendationId,
       status: currentStatus,
       logFilePath: logger?.logFilePath,
@@ -331,7 +341,7 @@ export async function runRecommendationCommand(
     logger?.finalize(false);
     return {
       success: false,
-      error: errorMsg,
+      error: err instanceof Error ? err : new Error(errorMsg),
       logFilePath: logger?.logFilePath,
     };
   }
diff --git a/src/cli/operations/recommendation/types.ts b/src/cli/operations/recommendation/types.ts
index 426ba84a8..74393a33b 100644
--- a/src/cli/operations/recommendation/types.ts
+++ b/src/cli/operations/recommendation/types.ts
@@ -1,6 +1,7 @@
 /**
  * Shared types for the recommendation feature.
  */
+import type { Result } from '../../../lib/types';
 import type { RecommendationResult, RecommendationType } from '../../aws/agentcore-recommendation';
 
 export type { RecommendationType } from '../../aws/agentcore-recommendation';
@@ -56,17 +57,13 @@ export interface RunRecommendationCommandOptions {
   onStarted?: (info: { recommendationId: string; region: string }) => void;
 }
 
-export interface RunRecommendationCommandResult {
-  success: boolean;
-  error?: string;
-  recommendationId?: string;
-  status?: string;
-  /** The recommendation result from the API (populated on COMPLETED) */
+export type RunRecommendationCommandResult = Result<{
   result?: RecommendationResult;
-  /** Resolved AWS region used for the recommendation */
   region?: string;
+}> & {
+  recommendationId?: string;
+  status?: string;
   startedAt?: string;
   completedAt?: string;
-  /** Path to the execution log file */
   logFilePath?: string;
-}
+};
diff --git a/src/cli/operations/remove/__tests__/remove-agent-ops.test.ts b/src/cli/operations/remove/__tests__/remove-agent-ops.test.ts
index fb2b9fedc..ee955342c 100644
--- a/src/cli/operations/remove/__tests__/remove-agent-ops.test.ts
+++ b/src/cli/operations/remove/__tests__/remove-agent-ops.test.ts
@@ -87,7 +87,10 @@ describe('remove', () => {
 
     const result = await primitive.remove('Missing');
 
-    expect(result).toEqual({ success: false, error: 'Agent "Missing" not found.' });
+    expect(result).toEqual({
+      success: false,
+      error: expect.objectContaining({ message: 'Agent "Missing" not found.' }),
+    });
   });
 
   it('returns error on exception', async () => {
@@ -95,6 +98,6 @@ describe('remove', () => {
 
     const result = await primitive.remove('Agent1');
 
-    expect(result).toEqual({ success: false, error: 'read fail' });
+    expect(result).toEqual({ success: false, error: expect.objectContaining({ message: 'read fail' }) });
   });
 });
diff --git a/src/cli/operations/remove/__tests__/remove-gateway-ops.test.ts b/src/cli/operations/remove/__tests__/remove-gateway-ops.test.ts
index 54293df5a..e06aa4f78 100644
--- a/src/cli/operations/remove/__tests__/remove-gateway-ops.test.ts
+++ b/src/cli/operations/remove/__tests__/remove-gateway-ops.test.ts
@@ -101,7 +101,10 @@ describe('remove', () => {
 
     const result = await primitive.remove('missing');
 
-    expect(result).toEqual({ success: false, error: 'Gateway "missing" not found.' });
+    expect(result).toEqual({
+      success: false,
+      error: expect.objectContaining({ message: 'Gateway "missing" not found.' }),
+    });
   });
 
   it('returns error on exception', async () => {
@@ -109,6 +112,6 @@ describe('remove', () => {
 
     const result = await primitive.remove('gw1');
 
-    expect(result).toEqual({ success: false, error: 'read fail' });
+    expect(result).toEqual({ success: false, error: expect.objectContaining({ message: 'read fail' }) });
   });
 });
diff --git a/src/cli/operations/remove/__tests__/remove-identity-ops.test.ts b/src/cli/operations/remove/__tests__/remove-identity-ops.test.ts
index 1b1bbb8e7..6610b2950 100644
--- a/src/cli/operations/remove/__tests__/remove-identity-ops.test.ts
+++ b/src/cli/operations/remove/__tests__/remove-identity-ops.test.ts
@@ -93,7 +93,10 @@ describe('remove', () => {
 
     const result = await primitive.remove('Missing');
 
-    expect(result).toEqual({ success: false, error: 'Credential "Missing" not found.' });
+    expect(result).toEqual({
+      success: false,
+      error: expect.objectContaining({ message: 'Credential "Missing" not found.' }),
+    });
   });
 
   it('returns error on exception', async () => {
@@ -101,6 +104,6 @@ describe('remove', () => {
 
     const result = await primitive.remove('Cred1');
 
-    expect(result).toEqual({ success: false, error: 'read fail' });
+    expect(result).toEqual({ success: false, error: expect.objectContaining({ message: 'read fail' }) });
   });
 });
diff --git a/src/cli/operations/remove/__tests__/remove-memory-ops.test.ts b/src/cli/operations/remove/__tests__/remove-memory-ops.test.ts
index d42bedb94..0ef487340 100644
--- a/src/cli/operations/remove/__tests__/remove-memory-ops.test.ts
+++ b/src/cli/operations/remove/__tests__/remove-memory-ops.test.ts
@@ -84,7 +84,10 @@ describe('remove', () => {
 
     const result = await primitive.remove('Missing');
 
-    expect(result).toEqual({ success: false, error: 'Memory "Missing" not found.' });
+    expect(result).toEqual({
+      success: false,
+      error: expect.objectContaining({ message: 'Memory "Missing" not found.' }),
+    });
   });
 
   it('returns error on exception', async () => {
@@ -92,6 +95,6 @@ describe('remove', () => {
 
     const result = await primitive.remove('Mem1');
 
-    expect(result).toEqual({ success: false, error: 'read fail' });
+    expect(result).toEqual({ success: false, error: expect.objectContaining({ message: 'read fail' }) });
   });
 });
diff --git a/src/cli/operations/remove/remove-gateway-target.ts b/src/cli/operations/remove/remove-gateway-target.ts
index 0ceebf7eb..5a1f7e2d8 100644
--- a/src/cli/operations/remove/remove-gateway-target.ts
+++ b/src/cli/operations/remove/remove-gateway-target.ts
@@ -1,6 +1,7 @@
 import { ConfigIO } from '../../../lib';
 import type { AgentCoreCliMcpDefs, AgentCoreMcpSpec } from '../../../schema';
-import type { RemovalPreview, RemovalResult, SchemaChange } from './types';
+import { getErrorMessage } from '../../errors';
+import type { RemovalPreview, Result, SchemaChange } from './types';
 import { existsSync } from 'fs';
 import { rm } from 'fs/promises';
 import { join } from 'path';
@@ -155,7 +156,7 @@ function computeRemovedToolMcpDefs(
 /**
  * Remove a gateway target from the project.
  */
-export async function removeGatewayTarget(tool: RemovableGatewayTarget): Promise<RemovalResult> {
+export async function removeGatewayTarget(tool: RemovableGatewayTarget): Promise<Result> {
   try {
     const configIO = new ConfigIO();
     const project = await configIO.readProjectSpec();
@@ -172,11 +173,11 @@ export async function removeGatewayTarget(tool: RemovableGatewayTarget): Promise
 
     const gateway = mcpSpec.agentCoreGateways.find(g => g.name === tool.gatewayName);
     if (!gateway) {
-      return { success: false, error: `Gateway "${tool.gatewayName}" not found.` };
+      return { success: false, error: new Error(`Gateway "${tool.gatewayName}" not found.`) };
     }
     const target = gateway.targets.find(t => t.name === tool.name);
     if (!target) {
-      return { success: false, error: `Target "${tool.name}" not found in gateway "${tool.gatewayName}".` };
+      return { success: false, error: new Error(`Target "${tool.name}" not found in gateway "${tool.gatewayName}".`) };
     }
     if (target.compute?.implementation && 'path' in target.compute.implementation) {
       toolPath = target.compute.implementation.path;
@@ -200,7 +201,6 @@ export async function removeGatewayTarget(tool: RemovableGatewayTarget): Promise
 
     return { success: true };
   } catch (err) {
-    const message = err instanceof Error ? err.message : 'Unknown error';
-    return { success: false, error: message };
+    return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
   }
 }
diff --git a/src/cli/operations/remove/types.ts b/src/cli/operations/remove/types.ts
index 2194a66f7..18a2c565d 100644
--- a/src/cli/operations/remove/types.ts
+++ b/src/cli/operations/remove/types.ts
@@ -21,10 +21,7 @@ export interface RemovalPreview {
   schemaChanges: SchemaChange[];
 }
 
-/**
- * Result of a removal operation.
- */
-export type RemovalResult = { success: true } | { success: false; error: string };
+export type { Result } from '../../../lib/types';
 
 /**
  * Snapshot of all schemas before removal (for diff computation).
diff --git a/src/cli/operations/resolve-agent.ts b/src/cli/operations/resolve-agent.ts
index 8f8ee6ba3..165ad23d1 100644
--- a/src/cli/operations/resolve-agent.ts
+++ b/src/cli/operations/resolve-agent.ts
@@ -1,4 +1,5 @@
 import { ConfigIO } from '../../lib';
+import type { Result } from '../../lib/types';
 import type { AgentCoreProjectSpec, AwsDeploymentTargets, DeployedState } from '../../schema';
 
 export interface DeployedProjectConfig {
@@ -32,11 +33,11 @@ export async function loadDeployedProjectConfig(configIO: ConfigIO = new ConfigI
 export function resolveAgent(
   context: DeployedProjectConfig,
   options: { runtime?: string }
-): { success: true; agent: ResolvedAgent } | { success: false; error: string } {
+): Result<{ agent: ResolvedAgent }> {
   const { project, deployedState, awsTargets } = context;
 
   if (project.runtimes.length === 0) {
-    return { success: false, error: 'No runtimes defined in agentcore.json' };
+    return { success: false, error: new Error('No runtimes defined in agentcore.json') };
   }
 
   // Resolve runtime
@@ -45,7 +46,7 @@ export function resolveAgent(
   if (!options.runtime && project.runtimes.length > 1) {
     return {
       success: false,
-      error: `Multiple runtimes found. Use --runtime to specify one: ${runtimeNames.join(', ')}`,
+      error: new Error(`Multiple runtimes found. Use --runtime to specify one: ${runtimeNames.join(', ')}`),
     };
   }
 
@@ -54,18 +55,18 @@ export function resolveAgent(
   if (options.runtime && !agentSpec) {
     return {
       success: false,
-      error: `Runtime '${options.runtime}' not found. Available: ${runtimeNames.join(', ')}`,
+      error: new Error(`Runtime '${options.runtime}' not found. Available: ${runtimeNames.join(', ')}`),
     };
   }
 
   if (!agentSpec) {
-    return { success: false, error: 'No runtimes defined in agentcore.json' };
+    return { success: false, error: new Error('No runtimes defined in agentcore.json') };
   }
 
   // Resolve target
   const targetNames = Object.keys(deployedState.targets);
   if (targetNames.length === 0) {
-    return { success: false, error: 'No deployed targets found. Run `agentcore deploy` first.' };
+    return { success: false, error: new Error('No deployed targets found. Run `agentcore deploy` first.') };
   }
   const selectedTargetName = targetNames[0]!;
 
@@ -73,7 +74,7 @@ export function resolveAgent(
   const targetConfig = awsTargets.find(t => t.name === selectedTargetName);
 
   if (!targetConfig) {
-    return { success: false, error: `Target config '${selectedTargetName}' not found in aws-targets` };
+    return { success: false, error: new Error(`Target config '${selectedTargetName}' not found in aws-targets`) };
   }
 
   // Get the deployed state for this specific agent
@@ -82,7 +83,9 @@ export function resolveAgent(
   if (!agentState) {
     return {
       success: false,
-      error: `Runtime '${agentSpec.name}' is not deployed to target '${selectedTargetName}'. Run 'agentcore deploy' first.`,
+      error: new Error(
+        `Runtime '${agentSpec.name}' is not deployed to target '${selectedTargetName}'. Run 'agentcore deploy' first.`
+      ),
     };
   }
 
diff --git a/src/cli/operations/traces/__tests__/get-trace.test.ts b/src/cli/operations/traces/__tests__/get-trace.test.ts
index c6fda22f4..6611389f0 100644
--- a/src/cli/operations/traces/__tests__/get-trace.test.ts
+++ b/src/cli/operations/traces/__tests__/get-trace.test.ts
@@ -62,12 +62,15 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.records).toHaveLength(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.records![0]).toEqual({
       '@timestamp': '2024-01-01T00:00:00Z',
       '@message': { traceId: 'abc123', spanId: 'span1' },
       '@ptr': 'ptr-value-1',
     });
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.records![1]).toEqual({
       '@timestamp': '2024-01-01T00:00:01Z',
       '@message': { traceId: 'abc123', spanId: 'span2' },
@@ -81,7 +84,8 @@ describe('fetchTraceRecords', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Invalid trace ID format');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Invalid trace ID format');
     expect(mockSend).not.toHaveBeenCalled();
   });
 
@@ -94,7 +98,8 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('No trace data found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('No trace data found');
   });
 
   it('returns error when query fails to start', async () => {
@@ -103,7 +108,8 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Failed to start CloudWatch Logs Insights query');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Failed to start CloudWatch Logs Insights query');
   });
 
   it('returns error when query status is Failed', async () => {
@@ -112,7 +118,8 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('failed');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('failed');
   });
 
   it('preserves @ptr when present in CloudWatch response', async () => {
@@ -130,7 +137,9 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.records).toHaveLength(1);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.records![0]!['@ptr']).toBe('cw-ptr-123');
   });
 
@@ -148,6 +157,7 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.records![0]).not.toHaveProperty('@ptr');
   });
 
@@ -165,7 +175,9 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.records).toHaveLength(1);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.records![0]!['@message']).toBe('plain text message');
   });
 
@@ -177,8 +189,10 @@ describe('fetchTraceRecords', () => {
     const result = await fetchTraceRecords(baseOptions);
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Log group');
-    expect(result.error).toContain('not found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Log group');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('not found');
   });
 });
 
@@ -209,6 +223,7 @@ describe('getTrace', () => {
     });
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.filePath).toContain('test-trace.json');
     expect(fs.default.mkdirSync).toHaveBeenCalled();
     expect(fs.default.writeFileSync).toHaveBeenCalledWith('/tmp/test-trace.json', expect.stringContaining('"traceId"'));
@@ -227,7 +242,8 @@ describe('getTrace', () => {
     });
 
     expect(result.success).toBe(false);
-    expect(result.error).toContain('Invalid trace ID format');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toContain('Invalid trace ID format');
     expect(fs.default.writeFileSync).not.toHaveBeenCalled();
   });
 });
diff --git a/src/cli/operations/traces/__tests__/list-traces.test.ts b/src/cli/operations/traces/__tests__/list-traces.test.ts
index 0bbe884de..a5513f439 100644
--- a/src/cli/operations/traces/__tests__/list-traces.test.ts
+++ b/src/cli/operations/traces/__tests__/list-traces.test.ts
@@ -39,13 +39,16 @@ describe('listTraces', () => {
     const result = await listTraces(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.traces).toHaveLength(2);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.traces![0]).toEqual({
       traceId: 'trace-1',
       timestamp: '2024-01-01T00:05:00Z',
       sessionId: 'sess-1',
       spanCount: '12',
     });
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.traces![1]).toEqual({
       traceId: 'trace-2',
       timestamp: '2024-01-01T00:03:00Z',
@@ -67,7 +70,9 @@ describe('listTraces', () => {
     const result = await listTraces(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.traces).toHaveLength(1);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.traces![0]!.traceId).toBe('trace-1');
   });
 
@@ -80,6 +85,7 @@ describe('listTraces', () => {
     const result = await listTraces(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses discriminated union field
     expect(result.traces![0]!.timestamp).toBe('2024-01-01T00:00:00Z');
   });
 
@@ -92,19 +98,21 @@ describe('listTraces', () => {
     const result = await listTraces(baseOptions);
 
     expect(result.success).toBe(true);
+    // @ts-expect-error -- test accesses success-branch field
     expect(result.traces).toHaveLength(0);
   });
 
   it('propagates errors from runInsightsQuery', async () => {
     mockRunInsightsQuery.mockResolvedValueOnce({
       success: false,
-      error: 'Log group not found',
+      error: new Error('Log group not found'),
     });
 
     const result = await listTraces(baseOptions);
 
     expect(result.success).toBe(false);
-    expect(result.error).toBe('Log group not found');
+    // @ts-expect-error -- test accesses failure-branch field
+    expect(result.error.message).toBe('Log group not found');
   });
 
   it('passes correct log group name and default limit', async () => {
diff --git a/src/cli/operations/traces/get-trace.ts b/src/cli/operations/traces/get-trace.ts
index a87f10a65..1de18e426 100644
--- a/src/cli/operations/traces/get-trace.ts
+++ b/src/cli/operations/traces/get-trace.ts
@@ -23,9 +23,9 @@ async function fetchSpans(
   traceId: string,
   startTime?: number,
   endTime?: number
-): Promise<{ success: boolean; spans?: CloudWatchSpanRecord[]; error?: string }> {
+): Promise<{ success: boolean; spans?: CloudWatchSpanRecord[]; error?: Error }> {
   if (!TRACE_ID_PATTERN.test(traceId)) {
-    return { success: false, error: 'Invalid trace ID format. Expected a hex string (e.g., abc123def456).' };
+    return { success: false, error: new Error('Invalid trace ID format. Expected a hex string (e.g., abc123def456).') };
   }
 
   const result = await runInsightsQuery({
@@ -82,7 +82,7 @@ export async function fetchTraceRecords(options: FetchTraceRecordsOptions): Prom
   const { region, runtimeId, traceId, includeSpans } = options;
 
   if (!TRACE_ID_PATTERN.test(traceId)) {
-    return { success: false, error: 'Invalid trace ID format. Expected a hex string (e.g., abc123def456).' };
+    return { success: false, error: new Error('Invalid trace ID format. Expected a hex string (e.g., abc123def456).') };
   }
 
   const [recordsResult, spansResult] = await Promise.all([
@@ -106,7 +106,7 @@ export async function fetchTraceRecords(options: FetchTraceRecordsOptions): Prom
   const traceData = recordsResult.rows ?? [];
 
   if (traceData.length === 0 && (!spansResult || (spansResult.spans ?? []).length === 0)) {
-    return { success: false, error: `No trace data found for trace ID: ${traceId}` };
+    return { success: false, error: new Error(`No trace data found for trace ID: ${traceId}`) };
   }
 
   const records: CloudWatchTraceRecord[] = traceData.map(entry => {
@@ -146,7 +146,7 @@ export async function getTrace(options: GetTraceOptions): Promise<GetTraceResult
   const { region, runtimeId, agentName, traceId, outputPath } = options;
 
   if (!TRACE_ID_PATTERN.test(traceId)) {
-    return { success: false, error: 'Invalid trace ID format. Expected a hex string (e.g., abc123def456).' };
+    return { success: false, error: new Error('Invalid trace ID format. Expected a hex string (e.g., abc123def456).') };
   }
 
   const result = await runInsightsQuery({
@@ -165,7 +165,7 @@ export async function getTrace(options: GetTraceOptions): Promise<GetTraceResult
 
   const traceData = result.rows ?? [];
   if (traceData.length === 0) {
-    return { success: false, error: `No trace data found for trace ID: ${traceId}` };
+    return { success: false, error: new Error(`No trace data found for trace ID: ${traceId}`) };
   }
 
   const parsedTrace = traceData.map(entry => {
diff --git a/src/cli/operations/traces/insights-query.ts b/src/cli/operations/traces/insights-query.ts
index 5a4da2031..c77465e97 100644
--- a/src/cli/operations/traces/insights-query.ts
+++ b/src/cli/operations/traces/insights-query.ts
@@ -1,3 +1,4 @@
+import type { Result } from '../../../lib/types';
 import { getCredentialProvider } from '../../aws';
 import { CloudWatchLogsClient, GetQueryResultsCommand, StartQueryCommand } from '@aws-sdk/client-cloudwatch-logs';
 
@@ -11,11 +12,7 @@ export interface InsightsQueryOptions {
   endTime?: number;
 }
 
-export interface InsightsQueryResult {
-  success: boolean;
-  rows?: Record<string, string>[];
-  error?: string;
-}
+export type InsightsQueryResult = Result<{ rows: Record<string, string>[] }>;
 
 async function pollQueryResults(client: CloudWatchLogsClient, queryId: string): Promise<InsightsQueryResult> {
   for (let i = 0; i < 60; i++) {
@@ -26,7 +23,7 @@ async function pollQueryResults(client: CloudWatchLogsClient, queryId: string):
 
     if (status === 'Complete' || status === 'Failed' || status === 'Cancelled') {
       if (status !== 'Complete') {
-        return { success: false, error: `Query ${status.toLowerCase()}` };
+        return { success: false, error: new Error(`Query ${status.toLowerCase()}`) };
       }
 
       const rows = (queryResults.results ?? []).map(row => {
@@ -42,7 +39,7 @@ async function pollQueryResults(client: CloudWatchLogsClient, queryId: string):
     }
   }
 
-  return { success: false, error: 'Query timed out after 60 seconds' };
+  return { success: false, error: new Error('Query timed out after 60 seconds') };
 }
 
 export async function runInsightsQuery(options: InsightsQueryOptions): Promise<InsightsQueryResult> {
@@ -68,7 +65,7 @@ export async function runInsightsQuery(options: InsightsQueryOptions): Promise<I
     );
 
     if (!startQuery.queryId) {
-      return { success: false, error: 'Failed to start CloudWatch Logs Insights query' };
+      return { success: false, error: new Error('Failed to start CloudWatch Logs Insights query') };
     }
 
     return await pollQueryResults(client, startQuery.queryId);
@@ -77,9 +74,11 @@ export async function runInsightsQuery(options: InsightsQueryOptions): Promise<I
     if (err.name === 'ResourceNotFoundException') {
       return {
         success: false,
-        error: `Log group '${logGroupName}' not found. The agent may not have been invoked yet, or traces may not be enabled.`,
+        error: new Error(
+          `Log group '${logGroupName}' not found. The agent may not have been invoked yet, or traces may not be enabled.`
+        ),
       };
     }
-    return { success: false, error: err.message ?? String(error) };
+    return { success: false, error: new Error(err.message ?? String(error)) };
   }
 }
diff --git a/src/cli/operations/traces/types.ts b/src/cli/operations/traces/types.ts
index fae88a83b..757fc3b39 100644
--- a/src/cli/operations/traces/types.ts
+++ b/src/cli/operations/traces/types.ts
@@ -1,3 +1,5 @@
+import type { Result } from '../../../lib/types';
+
 export interface CloudWatchTraceRecord {
   '@timestamp': string;
   '@message': unknown;
@@ -31,12 +33,7 @@ export interface FetchTraceRecordsOptions {
   includeSpans?: boolean;
 }
 
-export interface FetchTraceRecordsResult {
-  success: boolean;
-  records?: CloudWatchTraceRecord[];
-  spans?: CloudWatchSpanRecord[];
-  error?: string;
-}
+export type FetchTraceRecordsResult = Result<{ records: CloudWatchTraceRecord[]; spans?: CloudWatchSpanRecord[] }>;
 
 export interface GetTraceOptions {
   region: string;
@@ -48,11 +45,7 @@ export interface GetTraceOptions {
   endTime?: number;
 }
 
-export interface GetTraceResult {
-  success: boolean;
-  filePath?: string;
-  error?: string;
-}
+export type GetTraceResult = Result<{ filePath: string }>;
 
 export interface TraceEntry {
   traceId: string;
@@ -70,8 +63,4 @@ export interface ListTracesOptions {
   endTime?: number;
 }
 
-export interface ListTracesResult {
-  success: boolean;
-  traces?: TraceEntry[];
-  error?: string;
-}
+export type ListTracesResult = Result<{ traces: TraceEntry[] }>;
diff --git a/src/cli/primitives/ABTestPrimitive.ts b/src/cli/primitives/ABTestPrimitive.ts
index 9dd973571..4f0db08b8 100644
--- a/src/cli/primitives/ABTestPrimitive.ts
+++ b/src/cli/primitives/ABTestPrimitive.ts
@@ -2,10 +2,10 @@ import { findConfigRoot } from '../../lib';
 import type { ABTest } from '../../schema/schemas/primitives/ab-test';
 import { ABTestSchema } from '../../schema/schemas/primitives/ab-test';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { requireTTY } from '../tui/guards/tty';
 import { BasePrimitive } from './BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 export type GatewayChoice = { type: 'create-new' } | { type: 'existing-http'; name: string };
@@ -60,22 +60,22 @@ export class ABTestPrimitive extends BasePrimitive<AddABTestOptions, RemovableAB
   override readonly article = 'an';
   readonly primitiveSchema = ABTestSchema;
 
-  async add(options: AddABTestOptions): Promise<AddResult<{ abTestName: string }>> {
+  async add(options: AddABTestOptions): Promise<Result<{ abTestName: string }>> {
     try {
       const abTest = await this.createABTest(options);
       return { success: true, abTestName: abTest.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(testName: string, options?: { deleteGateway?: boolean }): Promise<RemovalResult> {
+  async remove(testName: string, options?: { deleteGateway?: boolean }): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const index = (project.abTests ?? []).findIndex(t => t.name === testName);
       if (index === -1) {
-        return { success: false, error: `AB test "${testName}" not found.` };
+        return { success: false, error: new Error(`AB test "${testName}" not found.`) };
       }
 
       const removedTest = project.abTests[index]!;
@@ -123,7 +123,7 @@ export class ABTestPrimitive extends BasePrimitive<AddABTestOptions, RemovableAB
 
       return { success: true };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -364,11 +364,11 @@ Target-Based Mode (--mode target-based)
               });
 
               if (cliOptions.json) {
-                console.log(JSON.stringify(result));
+                console.log(JSON.stringify(result.success ? result : { success: false, error: result.error.message }));
               } else if (result.success) {
                 console.log(`Added target-based AB test '${result.abTestName}'`);
               } else {
-                console.error(result.error);
+                console.error(result.error.message);
               }
               process.exit(result.success ? 0 : 1);
               return;
@@ -411,11 +411,11 @@ Target-Based Mode (--mode target-based)
             });
 
             if (cliOptions.json) {
-              console.log(JSON.stringify(result));
+              console.log(JSON.stringify(result.success ? result : { success: false, error: result.error.message }));
             } else if (result.success) {
               console.log(`Added AB test '${result.abTestName}'`);
             } else {
-              console.error(result.error);
+              console.error(result.error.message);
             }
             process.exit(result.success ? 0 : 1);
           } else {
@@ -475,7 +475,7 @@ Target-Based Mode (--mode target-based)
                 resourceType: this.kind,
                 resourceName: cliOptions.name,
                 message: result.success ? `Removed ${this.label.toLowerCase()} '${cliOptions.name}'` : undefined,
-                error: !result.success ? result.error : undefined,
+                error: !result.success ? result.error.message : undefined,
               })
             );
             process.exit(result.success ? 0 : 1);
@@ -598,12 +598,12 @@ Target-Based Mode (--mode target-based)
     return abTest;
   }
 
-  async addTargetBased(options: AddTargetBasedABTestOptions): Promise<AddResult<{ abTestName: string }>> {
+  async addTargetBased(options: AddTargetBasedABTestOptions): Promise<Result<{ abTestName: string }>> {
     try {
       const abTest = await this.createTargetBasedABTest(options);
       return { success: true, abTestName: abTest.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
diff --git a/src/cli/primitives/AgentPrimitive.tsx b/src/cli/primitives/AgentPrimitive.tsx
index b9873990b..528af65ca 100644
--- a/src/cli/primitives/AgentPrimitive.tsx
+++ b/src/cli/primitives/AgentPrimitive.tsx
@@ -34,7 +34,7 @@ import {
 } from '../operations/agent/generate';
 import { executeImportAgent } from '../operations/agent/import';
 import { setupPythonProject } from '../operations/python';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import {
   AgentType,
@@ -55,7 +55,7 @@ import { BasePrimitive } from './BasePrimitive';
 import { CredentialPrimitive } from './CredentialPrimitive';
 import { buildAuthorizerConfigFromJwtConfig, createManagedOAuthCredential } from './auth-utils';
 import { computeDefaultCredentialEnvVarName } from './credential-utils';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { mkdirSync } from 'fs';
 import { dirname, join } from 'path';
@@ -115,17 +115,17 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
     };
   }
 
-  async add(options: AddAgentOptions): Promise<AddResult<{ agentName: string; agentPath?: string }>> {
+  async add(options: AddAgentOptions): Promise<Result<{ agentName: string; agentPath?: string }>> {
     try {
       const configBaseDir = findConfigRoot();
       if (!configBaseDir) {
-        return { success: false, error: new NoProjectError().message };
+        return { success: false, error: new NoProjectError() };
       }
 
       const configIO = new ConfigIO({ baseDir: configBaseDir });
 
       if (!configIO.configExists('project')) {
-        return { success: false, error: new NoProjectError().message };
+        return { success: false, error: new NoProjectError() };
       }
 
       const project = await configIO.readProjectSpec();
@@ -133,7 +133,9 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
       if (existingAgent) {
         return {
           success: false,
-          error: `Agent "${options.name}" already exists. To update its configuration, edit agentcore/agentcore.json directly.`,
+          error: new Error(
+            `Agent "${options.name}" already exists. To update its configuration, edit agentcore/agentcore.json directly.`
+          ),
         };
       }
 
@@ -145,17 +147,17 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
         return await this.handleCreatePath(options, configBaseDir);
       }
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(agentName: string): Promise<RemovalResult> {
+  async remove(agentName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const agentIndex = project.runtimes.findIndex(a => a.name === agentName);
       if (agentIndex === -1) {
-        return { success: false, error: `Agent "${agentName}" not found.` };
+        return { success: false, error: new Error(`Agent "${agentName}" not found.`) };
       }
 
       // Remove agent (credentials preserved for potential reuse)
@@ -164,8 +166,7 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -333,7 +334,7 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
             });
 
             if (!result.success) {
-              throw new Error(result.error);
+              throw result.error;
             }
 
             if (cliOptions.json) {
@@ -400,7 +401,7 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
   private async handleCreatePath(
     options: AddAgentOptions,
     configBaseDir: string
-  ): Promise<AddResult<{ agentName: string; agentPath?: string }>> {
+  ): Promise<Result<{ agentName: string; agentPath?: string }>> {
     const projectRoot = dirname(configBaseDir);
     const configIO = new ConfigIO({ baseDir: configBaseDir });
     const project = await configIO.readProjectSpec();
@@ -510,7 +511,7 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
   private async handleImportPath(
     options: AddAgentOptions,
     configBaseDir: string
-  ): Promise<AddResult<{ agentName: string; agentPath?: string }>> {
+  ): Promise<Result<{ agentName: string; agentPath?: string }>> {
     return executeImportAgent({
       name: options.name,
       framework: options.framework,
@@ -532,7 +533,7 @@ export class AgentPrimitive extends BasePrimitive<AddAgentOptions, RemovableReso
     options: AddAgentOptions,
     configIO: ConfigIO,
     configBaseDir: string
-  ): Promise<AddResult<{ agentName: string; agentPath?: string }>> {
+  ): Promise<Result<{ agentName: string; agentPath?: string }>> {
     const codeLocation = options.codeLocation!.endsWith('/') ? options.codeLocation! : `${options.codeLocation!}/`;
 
     // Create the agent code directory so users know where to put their code
diff --git a/src/cli/primitives/BasePrimitive.ts b/src/cli/primitives/BasePrimitive.ts
index 149611c4f..1c689e491 100644
--- a/src/cli/primitives/BasePrimitive.ts
+++ b/src/cli/primitives/BasePrimitive.ts
@@ -4,7 +4,7 @@ import type { ResourceType } from '../commands/remove/types';
 import { getErrorMessage } from '../errors';
 import { requireTTY } from '../tui/guards/tty';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent, RemovableResource, RemovalPreview, RemovalResult } from './types';
+import type { AddScreenComponent, RemovableResource, RemovalPreview, Result } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import type { z } from 'zod';
 
@@ -37,12 +37,12 @@ export abstract class BasePrimitive<
    * Add a new resource of this type.
    * Each primitive owns its implementation entirely.
    */
-  abstract add(options: TAddOptions): Promise<AddResult>;
+  abstract add(options: TAddOptions): Promise<Result>;
 
   /**
    * Remove a resource by name.
    */
-  abstract remove(name: string): Promise<RemovalResult>;
+  abstract remove(name: string): Promise<Result>;
 
   /**
    * Preview what will be removed.
@@ -128,7 +128,7 @@ export abstract class BasePrimitive<
                 resourceName: cliOptions.name,
                 message: result.success ? `Removed ${this.label.toLowerCase()} '${cliOptions.name}'` : undefined,
                 note: result.success ? SOURCE_CODE_NOTE : undefined,
-                error: !result.success ? result.error : undefined,
+                error: !result.success ? result.error.message : undefined,
               })
             );
             process.exit(result.success ? 0 : 1);
diff --git a/src/cli/primitives/ConfigBundlePrimitive.ts b/src/cli/primitives/ConfigBundlePrimitive.ts
index 77f26205b..b10fb1dc1 100644
--- a/src/cli/primitives/ConfigBundlePrimitive.ts
+++ b/src/cli/primitives/ConfigBundlePrimitive.ts
@@ -2,9 +2,9 @@ import { findConfigRoot } from '../../lib';
 import type { ConfigBundle } from '../../schema';
 import { ConfigBundleSchema } from '../../schema';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { BasePrimitive } from './BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { readFileSync } from 'fs';
 
@@ -32,22 +32,22 @@ export class ConfigBundlePrimitive extends BasePrimitive<AddConfigBundleOptions,
   override readonly article = 'a';
   readonly primitiveSchema = ConfigBundleSchema;
 
-  async add(options: AddConfigBundleOptions): Promise<AddResult<{ bundleName: string }>> {
+  async add(options: AddConfigBundleOptions): Promise<Result<{ bundleName: string }>> {
     try {
       const bundle = await this.createConfigBundle(options);
       return { success: true, bundleName: bundle.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(bundleName: string): Promise<RemovalResult> {
+  async remove(bundleName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const index = (project.configBundles ?? []).findIndex(b => b.name === bundleName);
       if (index === -1) {
-        return { success: false, error: `Configuration bundle "${bundleName}" not found.` };
+        return { success: false, error: new Error(`Configuration bundle "${bundleName}" not found.`) };
       }
 
       project.configBundles.splice(index, 1);
@@ -55,7 +55,7 @@ export class ConfigBundlePrimitive extends BasePrimitive<AddConfigBundleOptions,
 
       return { success: true };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -170,11 +170,11 @@ export class ConfigBundlePrimitive extends BasePrimitive<AddConfigBundleOptions,
               });
 
               if (cliOptions.json) {
-                console.log(JSON.stringify(result));
+                console.log(JSON.stringify(result.success ? result : { success: false, error: result.error.message }));
               } else if (result.success) {
                 console.log(`Added configuration bundle '${result.bundleName}'`);
               } else {
-                console.error(result.error);
+                console.error(result.error.message);
               }
               process.exit(result.success ? 0 : 1);
             } else {
diff --git a/src/cli/primitives/CredentialPrimitive.tsx b/src/cli/primitives/CredentialPrimitive.tsx
index 9607094f8..1d82c8f49 100644
--- a/src/cli/primitives/CredentialPrimitive.tsx
+++ b/src/cli/primitives/CredentialPrimitive.tsx
@@ -3,13 +3,13 @@ import type { Credential, ModelProvider } from '../../schema';
 import { CredentialSchema } from '../../schema';
 import { validateAddCredentialOptions } from '../commands/add/validate';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { CredentialType, standardize } from '../telemetry/schemas/common-shapes.js';
 import { requireTTY } from '../tui/guards/tty';
 import { BasePrimitive } from './BasePrimitive';
 import { computeDefaultCredentialEnvVarName } from './credential-utils';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 /**
@@ -72,22 +72,22 @@ export class CredentialPrimitive extends BasePrimitive<AddCredentialOptions, Rem
 
   protected override readonly article: string = 'a';
 
-  async add(options: AddCredentialOptions): Promise<AddResult<{ credentialName: string }>> {
+  async add(options: AddCredentialOptions): Promise<Result<{ credentialName: string }>> {
     try {
       const credential = await this.createCredential(options);
       return { success: true, credentialName: credential.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(credentialName: string, options?: { force?: boolean }): Promise<RemovalResult> {
+  async remove(credentialName: string, options?: { force?: boolean }): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const credentialIndex = project.credentials.findIndex(c => c.name === credentialName);
       if (credentialIndex === -1) {
-        return { success: false, error: `Credential "${credentialName}" not found.` };
+        return { success: false, error: new Error(`Credential "${credentialName}" not found.`) };
       }
 
       const credential = project.credentials[credentialIndex]!;
@@ -96,7 +96,9 @@ export class CredentialPrimitive extends BasePrimitive<AddCredentialOptions, Rem
       if ('managed' in credential && credential.managed && !options?.force) {
         return {
           success: false,
-          error: `Credential "${credentialName}" is managed by the CLI and cannot be removed. Use force to override.`,
+          error: new Error(
+            `Credential "${credentialName}" is managed by the CLI and cannot be removed. Use force to override.`
+          ),
         };
       }
 
@@ -106,7 +108,9 @@ export class CredentialPrimitive extends BasePrimitive<AddCredentialOptions, Rem
         const targetList = referencingTargets.map(t => t.name).join(', ');
         return {
           success: false,
-          error: `Credential "${credentialName}" is referenced by gateway target(s): ${targetList}. Use force to override.`,
+          error: new Error(
+            `Credential "${credentialName}" is referenced by gateway target(s): ${targetList}. Use force to override.`
+          ),
         };
       }
 
@@ -115,8 +119,7 @@ export class CredentialPrimitive extends BasePrimitive<AddCredentialOptions, Rem
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -328,7 +331,7 @@ export class CredentialPrimitive extends BasePrimitive<AddCredentialOptions, Rem
               const result = await this.add(addOptions);
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
diff --git a/src/cli/primitives/EvaluatorPrimitive.ts b/src/cli/primitives/EvaluatorPrimitive.ts
index ec7372b08..fc032a21c 100644
--- a/src/cli/primitives/EvaluatorPrimitive.ts
+++ b/src/cli/primitives/EvaluatorPrimitive.ts
@@ -2,7 +2,7 @@ import { findConfigRoot } from '../../lib';
 import type { EvaluationLevel, Evaluator, EvaluatorConfig } from '../../schema';
 import { EvaluationLevelSchema, EvaluatorSchema } from '../../schema';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { EvaluatorType, Level, standardize } from '../telemetry/schemas/common-shapes.js';
 import { renderCodeBasedEvaluatorTemplate } from '../templates/EvaluatorRenderer';
@@ -14,7 +14,7 @@ import {
   validateInstructionPlaceholders,
 } from '../tui/screens/evaluator/types';
 import { BasePrimitive } from './BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { existsSync } from 'node:fs';
 import { rm } from 'node:fs/promises';
@@ -41,7 +41,7 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
   override readonly article = 'an';
   readonly primitiveSchema = EvaluatorSchema;
 
-  async add(options: AddEvaluatorOptions): Promise<AddResult<{ evaluatorName: string; codePath?: string }>> {
+  async add(options: AddEvaluatorOptions): Promise<Result<{ evaluatorName: string; codePath?: string }>> {
     try {
       const evaluator = await this.createEvaluator(options);
 
@@ -57,17 +57,17 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
 
       return { success: true, evaluatorName: evaluator.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(evaluatorName: string): Promise<RemovalResult> {
+  async remove(evaluatorName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const index = project.evaluators.findIndex(e => e.name === evaluatorName);
       if (index === -1) {
-        return { success: false, error: `Evaluator "${evaluatorName}" not found.` };
+        return { success: false, error: new Error(`Evaluator "${evaluatorName}" not found.`) };
       }
 
       // Warn if referenced by online eval configs
@@ -76,7 +76,9 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
         const configNames = referencingConfigs.map(c => c.name).join(', ');
         return {
           success: false,
-          error: `Evaluator "${evaluatorName}" is referenced by online eval config(s): ${configNames}. Remove those references first.`,
+          error: new Error(
+            `Evaluator "${evaluatorName}" is referenced by online eval config(s): ${configNames}. Remove those references first.`
+          ),
         };
       }
 
@@ -96,7 +98,7 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
 
       return { success: true };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -249,7 +251,7 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
 
                 if (!cliOptions.instructions) {
                   const level = levelResult.data!;
-                  const placeholders = LEVEL_PLACEHOLDERS[level].map(p => `{${p}}`).join(', ');
+                  const placeholders = LEVEL_PLACEHOLDERS[level].map((p: string) => `{${p}}`).join(', ');
                   fail(
                     `--instructions is required in non-interactive mode (or use --config). ` +
                       `Must include at least one placeholder for ${level}: ${placeholders}`
@@ -296,7 +298,7 @@ export class EvaluatorPrimitive extends BasePrimitive<AddEvaluatorOptions, Remov
               });
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
diff --git a/src/cli/primitives/GatewayPrimitive.ts b/src/cli/primitives/GatewayPrimitive.ts
index 625a3c4a5..270100032 100644
--- a/src/cli/primitives/GatewayPrimitive.ts
+++ b/src/cli/primitives/GatewayPrimitive.ts
@@ -11,7 +11,7 @@ import { AgentCoreGatewaySchema, PolicyEngineModeSchema } from '../../schema';
 import type { AddGatewayOptions as CLIAddGatewayOptions } from '../commands/add/types';
 import { validateAddGatewayOptions } from '../commands/add/validate';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { AuthorizerType, PolicyEngineMode, standardize } from '../telemetry/schemas/common-shapes.js';
 import { requireTTY } from '../tui/guards/tty';
@@ -19,7 +19,7 @@ import type { AddGatewayConfig } from '../tui/screens/mcp/types';
 import { BasePrimitive } from './BasePrimitive';
 import { buildAuthorizerConfigFromJwtConfig, createManagedOAuthCredential } from './auth-utils';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 /**
@@ -61,24 +61,24 @@ export class GatewayPrimitive extends BasePrimitive<AddGatewayOptions, Removable
   readonly label = 'Gateway';
   readonly primitiveSchema = AgentCoreGatewaySchema;
 
-  async add(options: AddGatewayOptions): Promise<AddResult<{ gatewayName: string }>> {
+  async add(options: AddGatewayOptions): Promise<Result<{ gatewayName: string }>> {
     try {
       const config = this.buildGatewayConfig(options);
       const result = await this.createGatewayFromWizard(config);
       return { success: true, gatewayName: result.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(gatewayName: string): Promise<RemovalResult> {
+  async remove(gatewayName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
       const mcpSpec = extractMcpSpec(project);
 
       const gateway = mcpSpec.agentCoreGateways.find(g => g.name === gatewayName);
       if (!gateway) {
-        return { success: false, error: `Gateway "${gatewayName}" not found.` };
+        return { success: false, error: new Error(`Gateway "${gatewayName}" not found.`) };
       }
 
       const newMcpSpec = this.computeRemovedGatewayMcpSpec(mcpSpec, gatewayName);
@@ -86,8 +86,7 @@ export class GatewayPrimitive extends BasePrimitive<AddGatewayOptions, Removable
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -218,7 +217,7 @@ export class GatewayPrimitive extends BasePrimitive<AddGatewayOptions, Removable
           });
 
           if (!result.success) {
-            throw new Error(result.error);
+            throw result.error;
           }
 
           if (cliOptions.json) {
@@ -270,7 +269,7 @@ export class GatewayPrimitive extends BasePrimitive<AddGatewayOptions, Removable
                 resourceName: cliOptions.name,
                 message: result.success ? `Removed gateway '${cliOptions.name}'` : undefined,
                 note: result.success ? SOURCE_CODE_NOTE : undefined,
-                error: !result.success ? result.error : undefined,
+                error: !result.success ? result.error.message : undefined,
               })
             );
             process.exit(result.success ? 0 : 1);
diff --git a/src/cli/primitives/GatewayTargetPrimitive.ts b/src/cli/primitives/GatewayTargetPrimitive.ts
index e8a1da996..780b1a0d3 100644
--- a/src/cli/primitives/GatewayTargetPrimitive.ts
+++ b/src/cli/primitives/GatewayTargetPrimitive.ts
@@ -13,7 +13,7 @@ import type { AddGatewayTargetOptions as CLIAddGatewayTargetOptions } from '../c
 import { validateAddGatewayTargetOptions } from '../commands/add/validate';
 import { getErrorMessage } from '../errors';
 import type { RemovableGatewayTarget } from '../operations/remove/remove-gateway-target';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import {
   GATEWAY_TARGET_TYPE_MAP,
@@ -33,7 +33,7 @@ import type {
 import { DEFAULT_HANDLER, DEFAULT_NODE_VERSION, DEFAULT_PYTHON_VERSION } from '../tui/screens/mcp/types';
 import { BasePrimitive } from './BasePrimitive';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent } from './types';
+import type { AddScreenComponent } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { existsSync } from 'fs';
 import { mkdir, readFile, rm, writeFile } from 'fs/promises';
@@ -70,22 +70,22 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
   readonly label = 'Gateway Target';
   readonly primitiveSchema = AgentCoreGatewayTargetSchema;
 
-  async add(options: AddGatewayTargetOptions): Promise<AddResult<{ toolName: string; sourcePath: string }>> {
+  async add(options: AddGatewayTargetOptions): Promise<Result<{ toolName: string; sourcePath: string }>> {
     try {
       const config = this.buildGatewayTargetConfig(options);
       const result = await this.createToolFromWizard(config);
       return { success: true, toolName: result.toolName, sourcePath: result.projectPath };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(name: string): Promise<RemovalResult> {
+  async remove(name: string): Promise<Result> {
     // Find the target by name to get its gateway info
     const tools = await this.getRemovable();
     const tool = tools.find(t => t.name === name);
     if (!tool) {
-      return { success: false, error: `Gateway target "${name}" not found.` };
+      return { success: false, error: new Error(`Gateway target "${name}" not found.`) };
     }
     return this.removeGatewayTarget(tool);
   }
@@ -183,7 +183,7 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
   /**
    * Remove a gateway target (with full target info).
    */
-  async removeGatewayTarget(tool: RemovableGatewayTarget): Promise<RemovalResult> {
+  async removeGatewayTarget(tool: RemovableGatewayTarget): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
       const mcpSpec = extractMcpSpec(project);
@@ -195,11 +195,14 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
 
       const gateway = mcpSpec.agentCoreGateways.find(g => g.name === tool.gatewayName);
       if (!gateway) {
-        return { success: false, error: `Gateway "${tool.gatewayName}" not found.` };
+        return { success: false, error: new Error(`Gateway "${tool.gatewayName}" not found.`) };
       }
       const target = gateway.targets.find(t => t.name === tool.name);
       if (!target) {
-        return { success: false, error: `Target "${tool.name}" not found in gateway "${tool.gatewayName}".` };
+        return {
+          success: false,
+          error: new Error(`Target "${tool.name}" not found in gateway "${tool.gatewayName}".`),
+        };
       }
       if (target.compute?.implementation && 'path' in target.compute.implementation) {
         toolPath = target.compute.implementation.path;
@@ -223,8 +226,7 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -475,7 +477,7 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
           });
 
           if (!result.success) {
-            throw new Error(result.error);
+            throw result.error;
           }
 
           if (cliOptions.json) {
@@ -518,7 +520,7 @@ export class GatewayTargetPrimitive extends BasePrimitive<AddGatewayTargetOption
                 resourceName: cliOptions.name,
                 message: result.success ? `Removed gateway target '${cliOptions.name}'` : undefined,
                 note: result.success ? SOURCE_CODE_NOTE : undefined,
-                error: !result.success ? result.error : undefined,
+                error: !result.success ? result.error.message : undefined,
               })
             );
             process.exit(result.success ? 0 : 1);
diff --git a/src/cli/primitives/MemoryPrimitive.tsx b/src/cli/primitives/MemoryPrimitive.tsx
index a0c15c2c3..a6205497d 100644
--- a/src/cli/primitives/MemoryPrimitive.tsx
+++ b/src/cli/primitives/MemoryPrimitive.tsx
@@ -16,12 +16,12 @@ import {
 } from '../../schema';
 import { DEFAULT_DELIVERY_TYPE, validateAddMemoryOptions } from '../commands/add/validate';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { requireTTY } from '../tui/guards/tty';
 import { DEFAULT_EVENT_EXPIRY } from '../tui/screens/memory/types';
 import { BasePrimitive } from './BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { z } from 'zod';
 
@@ -54,7 +54,7 @@ export class MemoryPrimitive extends BasePrimitive<AddMemoryOptions, RemovableMe
   readonly label = 'Memory';
   readonly primitiveSchema = MemorySchema;
 
-  async add(options: AddMemoryOptions): Promise<AddResult<{ memoryName: string }>> {
+  async add(options: AddMemoryOptions): Promise<Result<{ memoryName: string }>> {
     try {
       const strategies = options.strategies
         ? options.strategies
@@ -83,17 +83,17 @@ export class MemoryPrimitive extends BasePrimitive<AddMemoryOptions, RemovableMe
 
       return { success: true, memoryName: memory.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(memoryName: string): Promise<RemovalResult> {
+  async remove(memoryName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const memoryIndex = project.memories.findIndex(m => m.name === memoryName);
       if (memoryIndex === -1) {
-        return { success: false, error: `Memory "${memoryName}" not found.` };
+        return { success: false, error: new Error(`Memory "${memoryName}" not found.`) };
       }
 
       project.memories.splice(memoryIndex, 1);
@@ -101,8 +101,7 @@ export class MemoryPrimitive extends BasePrimitive<AddMemoryOptions, RemovableMe
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -218,7 +217,7 @@ export class MemoryPrimitive extends BasePrimitive<AddMemoryOptions, RemovableMe
               });
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
diff --git a/src/cli/primitives/OnlineEvalConfigPrimitive.ts b/src/cli/primitives/OnlineEvalConfigPrimitive.ts
index 6e4436ac9..f6b91d624 100644
--- a/src/cli/primitives/OnlineEvalConfigPrimitive.ts
+++ b/src/cli/primitives/OnlineEvalConfigPrimitive.ts
@@ -2,11 +2,11 @@ import { findConfigRoot } from '../../lib';
 import type { OnlineEvalConfig } from '../../schema';
 import { OnlineEvalConfigSchema } from '../../schema';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { requireTTY } from '../tui/guards/tty';
 import { BasePrimitive } from './BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 export interface AddOnlineEvalConfigOptions {
@@ -29,22 +29,22 @@ export class OnlineEvalConfigPrimitive extends BasePrimitive<AddOnlineEvalConfig
   override readonly article = 'an';
   readonly primitiveSchema = OnlineEvalConfigSchema;
 
-  async add(options: AddOnlineEvalConfigOptions): Promise<AddResult<{ configName: string }>> {
+  async add(options: AddOnlineEvalConfigOptions): Promise<Result<{ configName: string }>> {
     try {
       const config = await this.createOnlineEvalConfig(options);
       return { success: true, configName: config.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(configName: string): Promise<RemovalResult> {
+  async remove(configName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const index = project.onlineEvalConfigs.findIndex(c => c.name === configName);
       if (index === -1) {
-        return { success: false, error: `Online eval config "${configName}" not found.` };
+        return { success: false, error: new Error(`Online eval config "${configName}" not found.`) };
       }
 
       project.onlineEvalConfigs.splice(index, 1);
@@ -52,7 +52,7 @@ export class OnlineEvalConfigPrimitive extends BasePrimitive<AddOnlineEvalConfig
 
       return { success: true };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -159,7 +159,7 @@ export class OnlineEvalConfigPrimitive extends BasePrimitive<AddOnlineEvalConfig
               });
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
diff --git a/src/cli/primitives/PolicyEnginePrimitive.ts b/src/cli/primitives/PolicyEnginePrimitive.ts
index bb9b314d8..2a522336c 100644
--- a/src/cli/primitives/PolicyEnginePrimitive.ts
+++ b/src/cli/primitives/PolicyEnginePrimitive.ts
@@ -2,13 +2,13 @@ import { findConfigRoot } from '../../lib';
 import type { AgentCoreProjectSpec, PolicyEngine } from '../../schema';
 import { PolicyEngineModeSchema, PolicyEngineSchema } from '../../schema';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { AttachMode, standardize } from '../telemetry/schemas/common-shapes.js';
 import { requireTTY } from '../tui/guards/tty';
 import { BasePrimitive } from './BasePrimitive';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 export interface AddPolicyEngineOptions {
@@ -22,7 +22,7 @@ export class PolicyEnginePrimitive extends BasePrimitive<AddPolicyEngineOptions,
   readonly label = 'Policy Engine';
   readonly primitiveSchema = PolicyEngineSchema;
 
-  async add(options: AddPolicyEngineOptions): Promise<AddResult<{ engineName: string }>> {
+  async add(options: AddPolicyEngineOptions): Promise<Result<{ engineName: string }>> {
     try {
       const project = await this.readProjectSpec();
 
@@ -40,17 +40,17 @@ export class PolicyEnginePrimitive extends BasePrimitive<AddPolicyEngineOptions,
 
       return { success: true, engineName: engine.name };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(engineName: string): Promise<RemovalResult> {
+  async remove(engineName: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
       const index = project.policyEngines.findIndex(e => e.name === engineName);
       if (index === -1) {
-        return { success: false, error: `Policy engine "${engineName}" not found.` };
+        return { success: false, error: new Error(`Policy engine "${engineName}" not found.`) };
       }
 
       project.policyEngines.splice(index, 1);
@@ -70,8 +70,7 @@ export class PolicyEnginePrimitive extends BasePrimitive<AddPolicyEngineOptions,
 
       return { success: true };
     } catch (err) {
-      const message = err instanceof Error ? err.message : 'Unknown error';
-      return { success: false, error: message };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -251,7 +250,7 @@ export class PolicyEnginePrimitive extends BasePrimitive<AddPolicyEngineOptions,
               }
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
@@ -325,13 +324,13 @@ export class PolicyEnginePrimitive extends BasePrimitive<AddPolicyEngineOptions,
                   resourceName: cliOptions.name,
                   message: result.success ? `Removed policy engine '${cliOptions.name}'` : undefined,
                   note: result.success ? SOURCE_CODE_NOTE : undefined,
-                  error: !result.success ? result.error : undefined,
+                  error: !result.success ? result.error.message : undefined,
                 })
               );
             } else if (result.success) {
               console.log(`Removed policy engine '${cliOptions.name}'`);
             } else {
-              console.error(result.error);
+              console.error(result.error.message);
             }
             process.exit(result.success ? 0 : 1);
           } else {
diff --git a/src/cli/primitives/PolicyPrimitive.ts b/src/cli/primitives/PolicyPrimitive.ts
index beefe3008..19e0400b8 100644
--- a/src/cli/primitives/PolicyPrimitive.ts
+++ b/src/cli/primitives/PolicyPrimitive.ts
@@ -4,13 +4,13 @@ import { PolicySchema, ValidationModeSchema } from '../../schema';
 import { detectRegion } from '../aws';
 import { getPolicyGeneration, startPolicyGeneration } from '../aws/policy-generation';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { ValidationMode, standardize } from '../telemetry/schemas/common-shapes.js';
 import { requireTTY } from '../tui/guards/tty';
 import { BasePrimitive } from './BasePrimitive';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 import { existsSync, readFileSync } from 'fs';
 
@@ -34,13 +34,13 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
   readonly label = 'Policy';
   readonly primitiveSchema = PolicySchema;
 
-  async add(options: AddPolicyOptions): Promise<AddResult<{ policyName: string; engineName: string }>> {
+  async add(options: AddPolicyOptions): Promise<Result<{ policyName: string; engineName: string }>> {
     try {
       const sourceFlags = [options.statement, options.source, options.generate].filter(Boolean);
       if (sourceFlags.length > 1) {
         return {
           success: false,
-          error: 'Only one of --statement, --source, or --generate can be provided.',
+          error: new Error('Only one of --statement, --source, or --generate can be provided.'),
         };
       }
 
@@ -48,7 +48,7 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
 
       const engine = project.policyEngines.find(e => e.name === options.engine);
       if (!engine) {
-        return { success: false, error: `Policy engine "${options.engine}" not found.` };
+        return { success: false, error: new Error(`Policy engine "${options.engine}" not found.`) };
       }
 
       this.checkDuplicate(engine.policies, options.name, 'Policy');
@@ -57,11 +57,11 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
 
       if (options.source && !statement) {
         if (!existsSync(options.source)) {
-          return { success: false, error: `Source file not found: ${options.source}` };
+          return { success: false, error: new Error(`Source file not found: ${options.source}`) };
         }
         statement = readFileSync(options.source, 'utf-8').trim();
         if (!statement) {
-          return { success: false, error: `Source file is empty: ${options.source}` };
+          return { success: false, error: new Error(`Source file is empty: ${options.source}`) };
         }
       }
 
@@ -91,17 +91,18 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
         if (!engineId) {
           return {
             success: false,
-            error: `Policy engine "${options.engine}" is not deployed. Run \`agentcore deploy\` first.`,
+            error: new Error(`Policy engine "${options.engine}" is not deployed. Run \`agentcore deploy\` first.`),
           };
         }
         if (options.gateway && !gatewayArn) {
-          return { success: false, error: `Gateway "${options.gateway}" not found in deployed state.` };
+          return { success: false, error: new Error(`Gateway "${options.gateway}" not found in deployed state.`) };
         }
         if (!gatewayArn) {
           return {
             success: false,
-            error:
-              'No deployed gateway found. Policy generation requires a deployed gateway. Use --gateway <name> to specify one.',
+            error: new Error(
+              'No deployed gateway found. Policy generation requires a deployed gateway. Use --gateway <name> to specify one.'
+            ),
           };
         }
 
@@ -123,7 +124,7 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
       }
 
       if (!statement) {
-        return { success: false, error: 'Either --statement, --source, or --generate is required.' };
+        return { success: false, error: new Error('Either --statement, --source, or --generate is required.') };
       }
 
       const policy: Policy = {
@@ -139,7 +140,7 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
 
       return { success: true, policyName: policy.name, engineName: options.engine };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -148,7 +149,7 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
    * The composite key format is used by getRemovable() and the generic TUI remove flow.
    * The separate arguments form is used by the CLI --name + --engine flags.
    */
-  async remove(nameOrCompositeKey: string, engineName?: string): Promise<RemovalResult> {
+  async remove(nameOrCompositeKey: string, engineName?: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
@@ -167,7 +168,9 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
         if (matchingEngines.length > 1) {
           return {
             success: false,
-            error: `Policy "${resolvedPolicy}" exists in multiple engines: ${matchingEngines.map(e => e.name).join(', ')}. Use --engine to specify which one.`,
+            error: new Error(
+              `Policy "${resolvedPolicy}" exists in multiple engines: ${matchingEngines.map(e => e.name).join(', ')}. Use --engine to specify which one.`
+            ),
           };
         }
       }
@@ -185,10 +188,12 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
 
       return {
         success: false,
-        error: `Policy "${resolvedPolicy}" not found${resolvedEngine ? ` in engine "${resolvedEngine}"` : ''}.`,
+        error: new Error(
+          `Policy "${resolvedPolicy}" not found${resolvedEngine ? ` in engine "${resolvedEngine}"` : ''}.`
+        ),
       };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -328,7 +333,7 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
               });
 
               if (!result.success) {
-                throw new Error(result.error);
+                throw result.error;
               }
 
               if (cliOptions.json) {
@@ -410,13 +415,13 @@ export class PolicyPrimitive extends BasePrimitive<AddPolicyOptions, RemovablePo
                   resourceName: cliOptions.name,
                   message: result.success ? `Removed policy '${cliOptions.name}'` : undefined,
                   note: result.success ? SOURCE_CODE_NOTE : undefined,
-                  error: !result.success ? result.error : undefined,
+                  error: !result.success ? result.error.message : undefined,
                 })
               );
             } else if (result.success) {
               console.log(`Removed policy '${cliOptions.name}'`);
             } else {
-              console.error(result.error);
+              console.error(result.error.message);
             }
             process.exit(result.success ? 0 : 1);
           } else {
diff --git a/src/cli/primitives/RuntimeEndpointPrimitive.ts b/src/cli/primitives/RuntimeEndpointPrimitive.ts
index e055fd17a..9a75e75f3 100644
--- a/src/cli/primitives/RuntimeEndpointPrimitive.ts
+++ b/src/cli/primitives/RuntimeEndpointPrimitive.ts
@@ -3,11 +3,11 @@ import type { AgentCoreProjectSpec } from '../../schema';
 import { RuntimeEndpointSchema } from '../../schema';
 import type { ResourceType } from '../commands/remove/types';
 import { getErrorMessage } from '../errors';
-import type { RemovalPreview, RemovalResult, SchemaChange } from '../operations/remove/types';
+import type { RemovalPreview, Result, SchemaChange } from '../operations/remove/types';
 import { cliCommandRun } from '../telemetry/cli-command-run.js';
 import { BasePrimitive } from './BasePrimitive';
 import { SOURCE_CODE_NOTE } from './constants';
-import type { AddResult, AddScreenComponent, RemovableResource } from './types';
+import type { AddScreenComponent, RemovableResource } from './types';
 import type { Command } from '@commander-js/extra-typings';
 
 /**
@@ -39,14 +39,14 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
   readonly label = 'Runtime Endpoint';
   readonly primitiveSchema = RuntimeEndpointSchema;
 
-  async add(options: AddRuntimeEndpointOptions): Promise<AddResult> {
+  async add(options: AddRuntimeEndpointOptions): Promise<Result<Record<string, unknown>>> {
     try {
       const project = await this.readProjectSpec();
 
       // Find the parent runtime
       const runtime = project.runtimes.find(a => a.name === options.runtime);
       if (!runtime) {
-        return { success: false, error: `Runtime "${options.runtime}" not found.` };
+        return { success: false, error: new Error(`Runtime "${options.runtime}" not found.`) };
       }
 
       // Initialize endpoints dictionary if needed
@@ -56,14 +56,14 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
       if (runtime.endpoints[options.endpoint]) {
         return {
           success: false,
-          error: `Endpoint "${options.endpoint}" already exists on runtime "${options.runtime}".`,
+          error: new Error(`Endpoint "${options.endpoint}" already exists on runtime "${options.runtime}".`),
         };
       }
 
       // Validate version is a positive integer
       const version = options.version ?? 1;
       if (!Number.isInteger(version) || version < 1) {
-        return { success: false, error: `Version must be a positive integer (got ${version}).` };
+        return { success: false, error: new Error(`Version must be a positive integer (got ${version}).`) };
       }
 
       // Check version against latest deployed version
@@ -75,7 +75,9 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
             if (deployedRuntime?.runtimeVersion && version > deployedRuntime.runtimeVersion) {
               return {
                 success: false,
-                error: `Version ${version} exceeds latest deployed version ${deployedRuntime.runtimeVersion} for runtime "${options.runtime}".`,
+                error: new Error(
+                  `Version ${version} exceeds latest deployed version ${deployedRuntime.runtimeVersion} for runtime "${options.runtime}".`
+                ),
               };
             }
           }
@@ -104,11 +106,11 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
         version: config.version,
       };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
-  async remove(name: string): Promise<RemovalResult> {
+  async remove(name: string): Promise<Result> {
     try {
       const project = await this.readProjectSpec();
 
@@ -119,7 +121,7 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
         const endpointName = name.substring(slashIndex + 1);
         const runtime = project.runtimes.find(r => r.name === runtimeName);
         if (!runtime?.endpoints?.[endpointName]) {
-          return { success: false, error: `Runtime endpoint "${name}" not found.` };
+          return { success: false, error: new Error(`Runtime endpoint "${name}" not found.`) };
         }
         delete runtime.endpoints[endpointName];
         if (Object.keys(runtime.endpoints).length === 0) {
@@ -141,9 +143,9 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
         }
       }
 
-      return { success: false, error: `Runtime endpoint "${name}" not found.` };
+      return { success: false, error: new Error(`Runtime endpoint "${name}" not found.`) };
     } catch (err) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) };
     }
   }
 
@@ -263,7 +265,7 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
             });
 
             if (!result.success) {
-              throw new Error(result.error);
+              throw result.error;
             }
 
             if (cliOptions.json) {
@@ -304,7 +306,7 @@ export class RuntimeEndpointPrimitive extends BasePrimitive<AddRuntimeEndpointOp
                 resourceName: cliOptions.name,
                 message: result.success ? `Removed runtime endpoint '${cliOptions.name}'` : undefined,
                 note: result.success ? SOURCE_CODE_NOTE : undefined,
-                error: !result.success ? result.error : undefined,
+                error: !result.success ? result.error.message : undefined,
               })
             );
             process.exit(result.success ? 0 : 1);
diff --git a/src/cli/primitives/__tests__/ABTestPrimitive.test.ts b/src/cli/primitives/__tests__/ABTestPrimitive.test.ts
index 20ae26fa1..d0f22510e 100644
--- a/src/cli/primitives/__tests__/ABTestPrimitive.test.ts
+++ b/src/cli/primitives/__tests__/ABTestPrimitive.test.ts
@@ -65,8 +65,7 @@ describe('ABTestPrimitive', () => {
 
       const result = await primitive.add(validOptions);
 
-      expect(result.success).toBe(true);
-      expect(result).toHaveProperty('abTestName', 'MyTest');
+      expect(result).toEqual(expect.objectContaining({ success: true, abTestName: 'MyTest' }));
 
       const writtenSpec = mockWriteProjectSpec.mock.calls[0]![0];
       expect(writtenSpec.abTests).toHaveLength(1);
@@ -121,7 +120,10 @@ describe('ABTestPrimitive', () => {
       const result = await primitive.add(validOptions);
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('already exists') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('already exists') }),
+        })
       );
     });
 
@@ -130,7 +132,9 @@ describe('ABTestPrimitive', () => {
 
       const result = await primitive.add(validOptions);
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: 'disk read error' }));
+      expect(result).toEqual(
+        expect.objectContaining({ success: false, error: expect.objectContaining({ message: 'disk read error' }) })
+      );
     });
 
     it('returns error when writeProjectSpec fails', async () => {
@@ -139,7 +143,9 @@ describe('ABTestPrimitive', () => {
 
       const result = await primitive.add(validOptions);
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: 'disk write error' }));
+      expect(result).toEqual(
+        expect.objectContaining({ success: false, error: expect.objectContaining({ message: 'disk write error' }) })
+      );
     });
 
     it('returns error when variant weights do not sum to 100', async () => {
@@ -175,8 +181,8 @@ describe('ABTestPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toContain('NonExistent');
-        expect(result.error).toContain('not found');
+        expect(result.error.message).toContain('NonExistent');
+        expect(result.error.message).toContain('not found');
       }
     });
 
@@ -187,7 +193,7 @@ describe('ABTestPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toBe('io error');
+        expect(result.error.message).toBe('io error');
       }
     });
 
diff --git a/src/cli/primitives/__tests__/BasePrimitive.test.ts b/src/cli/primitives/__tests__/BasePrimitive.test.ts
index 830cd4244..55255191f 100644
--- a/src/cli/primitives/__tests__/BasePrimitive.test.ts
+++ b/src/cli/primitives/__tests__/BasePrimitive.test.ts
@@ -1,5 +1,5 @@
 import { BasePrimitive } from '../BasePrimitive';
-import type { AddResult, AddScreenComponent, RemovableResource, RemovalPreview, RemovalResult } from '../types';
+import type { AddScreenComponent, RemovableResource, RemovalPreview, Result } from '../types';
 import type { Command } from '@commander-js/extra-typings';
 import { describe, expect, it } from 'vitest';
 import { z } from 'zod';
@@ -10,11 +10,11 @@ class StubPrimitive extends BasePrimitive {
   readonly label = 'Stub';
   readonly primitiveSchema = z.object({ name: z.string() });
 
-  add(_options: Record<string, unknown>): Promise<AddResult> {
+  add(_options: Record<string, unknown>): Promise<Result> {
     return Promise.resolve({ success: true });
   }
 
-  remove(_name: string): Promise<RemovalResult> {
+  remove(_name: string): Promise<Result> {
     return Promise.resolve({ success: true });
   }
 
diff --git a/src/cli/primitives/__tests__/EvaluatorPrimitive.test.ts b/src/cli/primitives/__tests__/EvaluatorPrimitive.test.ts
index b41545d20..88e25e3c0 100644
--- a/src/cli/primitives/__tests__/EvaluatorPrimitive.test.ts
+++ b/src/cli/primitives/__tests__/EvaluatorPrimitive.test.ts
@@ -74,8 +74,7 @@ describe('EvaluatorPrimitive', () => {
         config: validConfig,
       });
 
-      expect(result.success).toBe(true);
-      expect(result).toHaveProperty('evaluatorName', 'MyEval');
+      expect(result).toEqual(expect.objectContaining({ success: true, evaluatorName: 'MyEval' }));
 
       const writtenSpec = mockWriteProjectSpec.mock.calls[0]![0];
       expect(writtenSpec.evaluators).toHaveLength(1);
@@ -108,7 +107,10 @@ describe('EvaluatorPrimitive', () => {
       });
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('already exists') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('already exists') }),
+        })
       );
     });
 
@@ -121,7 +123,9 @@ describe('EvaluatorPrimitive', () => {
         config: validConfig,
       });
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: 'disk read error' }));
+      expect(result).toEqual(
+        expect.objectContaining({ success: false, error: expect.objectContaining({ message: 'disk read error' }) })
+      );
     });
   });
 
@@ -145,8 +149,8 @@ describe('EvaluatorPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toContain('NonExistent');
-        expect(result.error).toContain('not found');
+        expect(result.error.message).toContain('NonExistent');
+        expect(result.error.message).toContain('not found');
       }
     });
 
@@ -159,8 +163,8 @@ describe('EvaluatorPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toContain('referenced by online eval config');
-        expect(result.error).toContain('MyOnlineConfig');
+        expect(result.error.message).toContain('referenced by online eval config');
+        expect(result.error.message).toContain('MyOnlineConfig');
       }
       expect(mockWriteProjectSpec).not.toHaveBeenCalled();
     });
@@ -172,7 +176,7 @@ describe('EvaluatorPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toBe('io error');
+        expect(result.error.message).toBe('io error');
       }
     });
   });
diff --git a/src/cli/primitives/__tests__/OnlineEvalConfigPrimitive.test.ts b/src/cli/primitives/__tests__/OnlineEvalConfigPrimitive.test.ts
index c81160a6c..814305711 100644
--- a/src/cli/primitives/__tests__/OnlineEvalConfigPrimitive.test.ts
+++ b/src/cli/primitives/__tests__/OnlineEvalConfigPrimitive.test.ts
@@ -52,8 +52,7 @@ describe('OnlineEvalConfigPrimitive', () => {
         samplingRate: 10,
       });
 
-      expect(result.success).toBe(true);
-      expect(result).toHaveProperty('configName', 'MyConfig');
+      expect(result).toEqual(expect.objectContaining({ success: true, configName: 'MyConfig' }));
 
       const writtenSpec = mockWriteProjectSpec.mock.calls[0]![0];
       expect(writtenSpec.onlineEvalConfigs).toHaveLength(1);
@@ -126,7 +125,10 @@ describe('OnlineEvalConfigPrimitive', () => {
       });
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('already exists') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('already exists') }),
+        })
       );
     });
 
@@ -140,7 +142,9 @@ describe('OnlineEvalConfigPrimitive', () => {
         samplingRate: 10,
       });
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: 'no project' }));
+      expect(result).toEqual(
+        expect.objectContaining({ success: false, error: expect.objectContaining({ message: 'no project' }) })
+      );
     });
   });
 
@@ -169,8 +173,8 @@ describe('OnlineEvalConfigPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toContain('NonExistent');
-        expect(result.error).toContain('not found');
+        expect(result.error.message).toContain('NonExistent');
+        expect(result.error.message).toContain('not found');
       }
     });
 
@@ -181,7 +185,7 @@ describe('OnlineEvalConfigPrimitive', () => {
 
       expect(result.success).toBe(false);
       if (!result.success) {
-        expect(result.error).toBe('io error');
+        expect(result.error.message).toBe('io error');
       }
     });
   });
diff --git a/src/cli/primitives/__tests__/RuntimeEndpointPrimitive.test.ts b/src/cli/primitives/__tests__/RuntimeEndpointPrimitive.test.ts
index 46fe426f5..433d0c0e2 100644
--- a/src/cli/primitives/__tests__/RuntimeEndpointPrimitive.test.ts
+++ b/src/cli/primitives/__tests__/RuntimeEndpointPrimitive.test.ts
@@ -87,7 +87,12 @@ describe('RuntimeEndpointPrimitive', () => {
         endpoint: 'prod',
       });
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: expect.stringContaining('not found') }));
+      expect(result).toEqual(
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('not found') }),
+        })
+      );
     });
 
     it('returns error when endpoint already exists', async () => {
@@ -100,7 +105,10 @@ describe('RuntimeEndpointPrimitive', () => {
       });
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('already exists') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('already exists') }),
+        })
       );
     });
 
@@ -134,7 +142,10 @@ describe('RuntimeEndpointPrimitive', () => {
       });
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('positive integer') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('positive integer') }),
+        })
       );
     });
 
@@ -181,7 +192,10 @@ describe('RuntimeEndpointPrimitive', () => {
       });
 
       expect(result).toEqual(
-        expect.objectContaining({ success: false, error: expect.stringContaining('exceeds latest deployed version') })
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('exceeds latest deployed version') }),
+        })
       );
     });
   });
@@ -223,7 +237,12 @@ describe('RuntimeEndpointPrimitive', () => {
 
       const result = await primitive.remove('MyRuntime/nonexistent');
 
-      expect(result).toEqual(expect.objectContaining({ success: false, error: expect.stringContaining('not found') }));
+      expect(result).toEqual(
+        expect.objectContaining({
+          success: false,
+          error: expect.objectContaining({ message: expect.stringContaining('not found') }),
+        })
+      );
     });
 
     it('cleans up empty endpoints dict after removing last endpoint', async () => {
diff --git a/src/cli/primitives/index.ts b/src/cli/primitives/index.ts
index 3f69da1ed..b609bedd0 100644
--- a/src/cli/primitives/index.ts
+++ b/src/cli/primitives/index.ts
@@ -24,4 +24,4 @@ export {
   getPrimitive,
 } from './registry';
 export { SOURCE_CODE_NOTE } from './constants';
-export type { AddResult, AddScreenComponent, RemovableResource, RemovalPreview, RemovalResult } from './types';
+export type { AddScreenComponent, RemovableResource, RemovalPreview, Result } from './types';
diff --git a/src/cli/primitives/types.ts b/src/cli/primitives/types.ts
index 73842c972..09564a87a 100644
--- a/src/cli/primitives/types.ts
+++ b/src/cli/primitives/types.ts
@@ -1,14 +1,7 @@
-import type { RemovalPreview, RemovalResult } from '../operations/remove/types';
+import type { RemovalPreview } from '../operations/remove/types';
 import type { ComponentType } from 'react';
 
-/**
- * Result of an add operation.
- * Use the generic parameter to type extra fields on the success branch:
- *   AddResult<{ agentName: string }> → success branch has typed agentName
- */
-export type AddResult<T extends Record<string, unknown> = Record<string, unknown>> =
-  | ({ success: true; message?: string } & T)
-  | { success: false; error: string };
+export type { Result } from '../../lib/types';
 
 /**
  * Represents a resource that can be removed.
@@ -21,7 +14,7 @@ export interface RemovableResource {
 /**
  * Re-export removal types from shared types.
  */
-export type { RemovalPreview, RemovalResult };
+export type { RemovalPreview };
 
 /**
  * Screen component type for TUI add flows.
diff --git a/src/cli/telemetry/cli-command-run.ts b/src/cli/telemetry/cli-command-run.ts
index 987f05730..ce36a1f31 100644
--- a/src/cli/telemetry/cli-command-run.ts
+++ b/src/cli/telemetry/cli-command-run.ts
@@ -1,5 +1,5 @@
 import { getErrorMessage } from '../errors';
-import type { AddResult } from '../primitives/types.js';
+import type { Result } from '../primitives/types.js';
 import { TelemetryClientAccessor } from './client-accessor.js';
 import type { Command, CommandAttrs } from './schemas/command-run.js';
 
@@ -44,8 +44,8 @@ export async function cliCommandRun<C extends Command>(
 export async function withAddTelemetry<C extends Command, T extends Record<string, unknown>>(
   command: C,
   attrs: CommandAttrs<C>,
-  fn: () => Promise<AddResult<T>>
-): Promise<AddResult<T>> {
+  fn: () => Promise<Result<T>>
+): Promise<Result<T>> {
   let client;
   try {
     client = await TelemetryClientAccessor.get();
@@ -53,18 +53,18 @@ export async function withAddTelemetry<C extends Command, T extends Record<strin
     return fn();
   }
 
-  let result: AddResult<T> | undefined;
+  let result: Result<T> | undefined;
   try {
     await client.withCommandRun(command, async () => {
       result = await fn();
-      if (!result.success) throw new Error(result.error);
+      if (!result.success) throw result.error;
       return attrs;
     });
   } catch (err) {
     // withCommandRun re-throws after recording failure telemetry.
     // result is set if fn() ran; if not, fn() itself threw.
     if (!result) {
-      return { success: false, error: getErrorMessage(err) };
+      return { success: false, error: err instanceof Error ? err : new Error(getErrorMessage(err)) } as Result<T>;
     }
   }
   return result!;
diff --git a/src/cli/tui/hooks/useCreateABTest.ts b/src/cli/tui/hooks/useCreateABTest.ts
index e54666074..6a197ce59 100644
--- a/src/cli/tui/hooks/useCreateABTest.ts
+++ b/src/cli/tui/hooks/useCreateABTest.ts
@@ -43,7 +43,7 @@ export function useCreateABTest() {
         enableOnCreate: config.enableOnCreate,
       });
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create AB test');
+        throw addResult.error ?? new Error('Failed to create AB test');
       }
       setStatus({ state: 'success' });
       return { ok: true as const, testName: config.name };
@@ -59,7 +59,7 @@ export function useCreateABTest() {
     try {
       const addResult = await abTestPrimitive.addTargetBased(config);
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create target-based AB test');
+        throw addResult.error ?? new Error('Failed to create target-based AB test');
       }
       setStatus({ state: 'success' });
       return { ok: true as const, testName: config.name };
diff --git a/src/cli/tui/hooks/useCreateConfigBundle.ts b/src/cli/tui/hooks/useCreateConfigBundle.ts
index 864501eed..c1f9ade7e 100644
--- a/src/cli/tui/hooks/useCreateConfigBundle.ts
+++ b/src/cli/tui/hooks/useCreateConfigBundle.ts
@@ -25,7 +25,7 @@ export function useCreateConfigBundle() {
         commitMessage: config.commitMessage,
       });
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create configuration bundle');
+        throw addResult.error ?? new Error('Failed to create configuration bundle');
       }
       setStatus({ state: 'success' });
       return { ok: true as const, bundleName: config.name };
diff --git a/src/cli/tui/hooks/useCreateEvaluator.ts b/src/cli/tui/hooks/useCreateEvaluator.ts
index f1cad666f..29c67764b 100644
--- a/src/cli/tui/hooks/useCreateEvaluator.ts
+++ b/src/cli/tui/hooks/useCreateEvaluator.ts
@@ -32,7 +32,7 @@ export function useCreateEvaluator() {
           })
       );
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create evaluator');
+        throw addResult.error ?? new Error('Failed to create evaluator');
       }
       setStatus({ state: 'success' });
       return { ok: true as const, evaluatorName: config.name, codePath: addResult.codePath };
diff --git a/src/cli/tui/hooks/useCreateMcp.ts b/src/cli/tui/hooks/useCreateMcp.ts
index ec91666d0..48fd12005 100644
--- a/src/cli/tui/hooks/useCreateMcp.ts
+++ b/src/cli/tui/hooks/useCreateMcp.ts
@@ -53,7 +53,7 @@ export function useCreateGateway() {
           })
       );
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create gateway');
+        throw addResult.error ?? new Error('Failed to create gateway');
       }
       const result: CreateGatewayResult = { name: config.name };
       setStatus({ state: 'success', result });
diff --git a/src/cli/tui/hooks/useCreateMemory.ts b/src/cli/tui/hooks/useCreateMemory.ts
index d4196582f..8ec1bf8ec 100644
--- a/src/cli/tui/hooks/useCreateMemory.ts
+++ b/src/cli/tui/hooks/useCreateMemory.ts
@@ -45,7 +45,7 @@ export function useCreateMemory() {
           })
       );
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create memory');
+        throw addResult.error ?? new Error('Failed to create memory');
       }
       // Read back the memory object
       const configIO = new ConfigIO();
diff --git a/src/cli/tui/hooks/useCreateOnlineEval.ts b/src/cli/tui/hooks/useCreateOnlineEval.ts
index b853fed05..608cfe0aa 100644
--- a/src/cli/tui/hooks/useCreateOnlineEval.ts
+++ b/src/cli/tui/hooks/useCreateOnlineEval.ts
@@ -38,7 +38,7 @@ export function useCreateOnlineEval() {
           })
       );
       if (!addResult.success) {
-        throw new Error(addResult.error ?? 'Failed to create online eval config');
+        throw addResult.error ?? new Error('Failed to create online eval config');
       }
       setStatus({ state: 'success' });
       return { ok: true as const, configName: config.name };
diff --git a/src/cli/tui/hooks/useRemove.ts b/src/cli/tui/hooks/useRemove.ts
index 7682479d3..9809d8670 100644
--- a/src/cli/tui/hooks/useRemove.ts
+++ b/src/cli/tui/hooks/useRemove.ts
@@ -1,6 +1,6 @@
 import type { ResourceType } from '../../commands/remove/types';
 import { RemoveLogger } from '../../logging';
-import type { RemovableGatewayTarget, RemovalPreview, RemovalResult } from '../../operations/remove';
+import type { RemovableGatewayTarget, RemovalPreview, Result } from '../../operations/remove';
 import type { RemovableCredential } from '../../primitives/CredentialPrimitive';
 import type { RemovableMemory } from '../../primitives/MemoryPrimitive';
 import type { RemovablePolicyResource } from '../../primitives/PolicyPrimitive';
@@ -60,7 +60,7 @@ function useRemovableResources<T>(loader: () => Promise<T[]>) {
  * All useRemove* hooks delegate to this.
  */
 function useRemoveResource<TIdentifier>(
-  removeFn: (id: TIdentifier) => Promise<RemovalResult>,
+  removeFn: (id: TIdentifier) => Promise<Result>,
   resourceType: ResourceType,
   getResourceName: (id: TIdentifier) => string
 ) {
@@ -83,7 +83,7 @@ function useRemoveResource<TIdentifier>(
         resourceType: resourceTypeRef.current,
         resourceName: getNameRef.current(id),
       });
-      logger.logRemoval(preview, result.success, result.success ? undefined : result.error);
+      logger.logRemoval(preview, result.success, result.success ? undefined : result.error.message);
       logPath = logger.getAbsoluteLogPath();
       setLogFilePath(logPath);
     }
@@ -291,10 +291,10 @@ export function useRemovalPreview() {
 
 interface RemovalState {
   isLoading: boolean;
-  result: RemovalResult | null;
+  result: Result | null;
 }
 
-type RemoveResult = RemovalResult & { logFilePath?: string };
+type RemoveResult = Result & { logFilePath?: string };
 
 export function useRemoveAgent() {
   return useRemoveResource(
diff --git a/src/cli/tui/screens/agent/useAddAgent.ts b/src/cli/tui/screens/agent/useAddAgent.ts
index e2fabe140..e849528d4 100644
--- a/src/cli/tui/screens/agent/useAddAgent.ts
+++ b/src/cli/tui/screens/agent/useAddAgent.ts
@@ -12,6 +12,7 @@ import { executeImportAgent } from '../../../operations/agent/import';
 import { buildAuthorizerConfigFromJwtConfig, createManagedOAuthCredential } from '../../../primitives/auth-utils';
 import { computeDefaultCredentialEnvVarName } from '../../../primitives/credential-utils';
 import { credentialPrimitive } from '../../../primitives/registry';
+import type { Result } from '../../../primitives/types';
 import { withAddTelemetry } from '../../../telemetry/cli-command-run.js';
 import {
   AgentType as AgentTypeEnum,
@@ -165,7 +166,7 @@ export function useAddAgent() {
         () => addAgentInner(config)
       );
       if (!result.success) {
-        return { ok: false, error: result.error };
+        return { ok: false, error: result.error.message };
       }
       return result.outcome;
     } finally {
@@ -180,26 +181,24 @@ export function useAddAgent() {
   return { addAgent, isLoading, reset };
 }
 
-type AddAgentInnerResult =
-  | { success: true; outcome: AddAgentCreateResult | AddAgentByoResult }
-  | { success: false; error: string };
+type AddAgentInnerResult = Result<{ outcome: AddAgentCreateResult | AddAgentByoResult }>;
 
 async function addAgentInner(config: AddAgentConfig): Promise<AddAgentInnerResult> {
   const configBaseDir = findConfigRoot();
   if (!configBaseDir) {
-    return { success: false, error: new NoProjectError().message };
+    return { success: false, error: new NoProjectError() };
   }
 
   const configIO = new ConfigIO({ baseDir: configBaseDir });
 
   if (!configIO.configExists('project')) {
-    return { success: false, error: new NoProjectError().message };
+    return { success: false, error: new NoProjectError() };
   }
 
   const project = await configIO.readProjectSpec();
   const existingAgent = project.runtimes.find(agent => agent.name === config.name);
   if (existingAgent) {
-    return { success: false, error: `Agent "${config.name}" already exists in this project.` };
+    return { success: false, error: new Error(`Agent "${config.name}" already exists in this project.`) };
   }
 
   let outcome: AddAgentCreateResult | AddAgentByoResult | AddAgentError;
@@ -212,7 +211,7 @@ async function addAgentInner(config: AddAgentConfig): Promise<AddAgentInnerResul
   }
 
   if (!outcome.ok) {
-    return { success: false, error: outcome.error };
+    return { success: false, error: new Error(outcome.error) };
   }
   return { success: true, outcome };
 }
@@ -344,7 +343,7 @@ async function handleImportPath(
   });
 
   if (!result.success) {
-    return { ok: false, error: result.error ?? 'Unknown error' };
+    return { ok: false, error: result.error?.message ?? 'Unknown error' };
   }
 
   return {
diff --git a/src/cli/tui/screens/create/useCreateFlow.ts b/src/cli/tui/screens/create/useCreateFlow.ts
index 9d1742810..07a05ca93 100644
--- a/src/cli/tui/screens/create/useCreateFlow.ts
+++ b/src/cli/tui/screens/create/useCreateFlow.ts
@@ -363,7 +363,7 @@ export function useCreateFlow(cwd: string): CreateFlowState {
                   sessionStorageMountPath: addAgentConfig.sessionStorageMountPath,
                 });
                 if (!importResult.success) {
-                  throw new Error(importResult.error ?? 'Import failed');
+                  throw importResult.error;
                 }
               } else {
                 // BYO path: just write config to project (no file generation)
diff --git a/src/cli/tui/screens/deploy/useDeployFlow.ts b/src/cli/tui/screens/deploy/useDeployFlow.ts
index b27b3e528..ed33ad3d0 100644
--- a/src/cli/tui/screens/deploy/useDeployFlow.ts
+++ b/src/cli/tui/screens/deploy/useDeployFlow.ts
@@ -648,8 +648,8 @@ export function useDeployFlow(options: DeployFlowOptions = {}): DeployFlowState
                 agentNames,
                 hasGateways,
               });
-              if (tsResult.error) {
-                logger.log(`Transaction search setup warning: ${tsResult.error}`, 'warn');
+              if (!tsResult.success) {
+                logger.log(`Transaction search setup warning: ${tsResult.error.message}`, 'warn');
               } else {
                 setDeployNotes(prev => [
                   ...prev,
diff --git a/src/cli/tui/screens/eval/EvalScreen.tsx b/src/cli/tui/screens/eval/EvalScreen.tsx
index 3f57999d9..b7cfc7efa 100644
--- a/src/cli/tui/screens/eval/EvalScreen.tsx
+++ b/src/cli/tui/screens/eval/EvalScreen.tsx
@@ -339,7 +339,7 @@ export function EvalScreen({ onExit }: EvalScreenProps) {
       }
       const result = handleListEvalRuns({});
       if (!result.success) {
-        setState({ phase: 'error', runs: [], error: result.error ?? 'Unknown error' });
+        setState({ phase: 'error', runs: [], error: result.error.message ?? 'Unknown error' });
         return;
       }
       setState({ phase: 'loaded', runs: result.runs ?? [], error: null });
diff --git a/src/cli/tui/screens/identity/useCreateIdentity.ts b/src/cli/tui/screens/identity/useCreateIdentity.ts
index e214d1e67..6f8095055 100644
--- a/src/cli/tui/screens/identity/useCreateIdentity.ts
+++ b/src/cli/tui/screens/identity/useCreateIdentity.ts
@@ -25,7 +25,7 @@ export function useCreateIdentity() {
         () => credentialPrimitive.add(config)
       );
       if (!result.success) {
-        throw new Error(result.error ?? 'Failed to create credential');
+        throw result.error ?? new Error('Failed to create credential');
       }
       // Read back the credential object
       const configIO = new ConfigIO();
diff --git a/src/cli/tui/screens/import/ImportFlow.tsx b/src/cli/tui/screens/import/ImportFlow.tsx
index ed82962d3..71a07c702 100644
--- a/src/cli/tui/screens/import/ImportFlow.tsx
+++ b/src/cli/tui/screens/import/ImportFlow.tsx
@@ -151,10 +151,10 @@ export function ImportFlow({ onBack, onNavigate }: ImportFlowProps) {
                   <Text dimColor>Name: </Text>
                   <Text>{result.resourceName}</Text>
                 </Text>
-                {result.resourceId && (
+                {(result.success ? result.resourceId : undefined) && (
                   <Text>
                     <Text dimColor>ID: </Text>
-                    <Text>{result.resourceId}</Text>
+                    <Text>{result.success ? result.resourceId : undefined}</Text>
                   </Text>
                 )}
               </Box>
diff --git a/src/cli/tui/screens/import/ImportProgressScreen.tsx b/src/cli/tui/screens/import/ImportProgressScreen.tsx
index 3771ffbab..aa8c6f9e6 100644
--- a/src/cli/tui/screens/import/ImportProgressScreen.tsx
+++ b/src/cli/tui/screens/import/ImportProgressScreen.tsx
@@ -59,9 +59,9 @@ export function ImportProgressScreen({
           onSuccess(result);
         } else {
           setSteps(prev =>
-            prev.map(s => (s.status === 'running' ? { ...s, status: 'error', error: result.error } : s))
+            prev.map(s => (s.status === 'running' ? { ...s, status: 'error', error: result.error.message } : s))
           );
-          onError(result.error ?? 'Import failed');
+          onError(result.error.message);
         }
       } else {
         // Starter toolkit
@@ -75,9 +75,9 @@ export function ImportProgressScreen({
           onSuccess(result);
         } else {
           setSteps(prev =>
-            prev.map(s => (s.status === 'running' ? { ...s, status: 'error', error: result.error } : s))
+            prev.map(s => (s.status === 'running' ? { ...s, status: 'error', error: result.error.message } : s))
           );
-          onError(result.error ?? 'Import failed');
+          onError(result.error.message);
         }
       }
     };
diff --git a/src/cli/tui/screens/online-eval/OnlineEvalDashboard.tsx b/src/cli/tui/screens/online-eval/OnlineEvalDashboard.tsx
index 03961473e..06115a0fc 100644
--- a/src/cli/tui/screens/online-eval/OnlineEvalDashboard.tsx
+++ b/src/cli/tui/screens/online-eval/OnlineEvalDashboard.tsx
@@ -156,7 +156,7 @@ export function OnlineEvalDashboard({ onExit }: OnlineEvalDashboardProps) {
       setState(prev => ({ ...prev, phase: 'toggling' }));
       void handlePauseResume({ name: item.name }, action).then(result => {
         if (!result.success) {
-          setState(prev => ({ ...prev, phase: 'loaded', error: result.error ?? 'Toggle failed' }));
+          setState(prev => ({ ...prev, phase: 'loaded', error: result.error.message ?? 'Toggle failed' }));
           return;
         }
         return fetchDashboardConfigs().then(configs => {
diff --git a/src/cli/tui/screens/policy/AddPolicyFlow.tsx b/src/cli/tui/screens/policy/AddPolicyFlow.tsx
index 9b3542cb8..64eaa4f5c 100644
--- a/src/cli/tui/screens/policy/AddPolicyFlow.tsx
+++ b/src/cli/tui/screens/policy/AddPolicyFlow.tsx
@@ -139,7 +139,7 @@ export function AddPolicyFlow({ isInteractive = true, onExit, onBack, onDev, onD
       () => policyEnginePrimitive.add({ name: engineName })
     );
     if (!result.success) {
-      setFlow({ name: 'error', message: result.error });
+      setFlow({ name: 'error', message: result.error.message });
       return;
     }
     setEngineNames(prev => [...prev, engineName]);
@@ -184,7 +184,7 @@ export function AddPolicyFlow({ isInteractive = true, onExit, onBack, onDev, onD
       setPolicyNames(prev => [...prev, config.name]);
       setFlow({ name: 'policy-success', policyName: config.name, engineName: config.engine });
     } else {
-      setFlow({ name: 'error', message: result.error });
+      setFlow({ name: 'error', message: result.error.message });
     }
   }, []);
 
diff --git a/src/cli/tui/screens/recommendation/RecommendationFlow.tsx b/src/cli/tui/screens/recommendation/RecommendationFlow.tsx
index b28344df3..f3604b67e 100644
--- a/src/cli/tui/screens/recommendation/RecommendationFlow.tsx
+++ b/src/cli/tui/screens/recommendation/RecommendationFlow.tsx
@@ -33,7 +33,12 @@ type FlowState =
       recommendationId?: string;
       region?: string;
     }
-  | { name: 'results'; result: RunRecommendationCommandResult; config: RecommendationWizardConfig; filePath?: string }
+  | {
+      name: 'results';
+      result: Extract<RunRecommendationCommandResult, { success: true }>;
+      config: RecommendationWizardConfig;
+      filePath?: string;
+    }
   | { name: 'creds-error'; message: string }
   | { name: 'error'; message: string; logFilePath?: string };
 
@@ -194,13 +199,17 @@ export function RecommendationFlow({ onExit }: RecommendationFlowProps) {
           setFlow(prev => {
             if (prev.name !== 'running') return prev;
             const steps = prev.steps.map(s =>
-              s.status === 'running' ? { ...s, status: 'error' as const, error: result.error } : s
+              s.status === 'running' ? { ...s, status: 'error' as const, error: result.error.message } : s
             );
             return { ...prev, steps };
           });
           await new Promise(resolve => setTimeout(resolve, 2000));
           if (cancelled) return;
-          setFlow({ name: 'error', message: result.error ?? 'Recommendation failed', logFilePath: result.logFilePath });
+          setFlow({
+            name: 'error',
+            message: result.error.message ?? 'Recommendation failed',
+            logFilePath: result.logFilePath,
+          });
           return;
         }
 
@@ -333,7 +342,7 @@ export function RecommendationFlow({ onExit }: RecommendationFlowProps) {
 // ─────────────────────────────────────────────────────────────────────────────
 
 interface ResultsViewProps {
-  result: RunRecommendationCommandResult;
+  result: Extract<RunRecommendationCommandResult, { success: true }>;
   config: RecommendationWizardConfig;
   filePath?: string;
   onRunAnother: () => void;
@@ -369,7 +378,7 @@ function ResultsView({ result, config, filePath, onRunAnother, onExit }: Results
           message: `New bundle version (${applyResult.newVersionId}) created with recommended changes. Local config updated.`,
         });
       } else {
-        setApplyStatus({ applied: false, message: applyResult.error ?? 'Unknown error' });
+        setApplyStatus({ applied: false, message: applyResult.error.message ?? 'Unknown error' });
       }
     } catch (err) {
       setApplyStatus({ applied: false, message: getErrorMessage(err) });
diff --git a/src/cli/tui/screens/recommendation/RecommendationScreen.tsx b/src/cli/tui/screens/recommendation/RecommendationScreen.tsx
index adac72ef8..eea776e50 100644
--- a/src/cli/tui/screens/recommendation/RecommendationScreen.tsx
+++ b/src/cli/tui/screens/recommendation/RecommendationScreen.tsx
@@ -152,7 +152,7 @@ export function RecommendationScreen({
         const { region } = await detectRegion();
         const agentResult = resolveAgent(context, { runtime: wizard.config.agent });
         if (!agentResult.success) {
-          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error });
+          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error.message });
           return;
         }
 
diff --git a/src/cli/tui/screens/remove/RemoveFlow.tsx b/src/cli/tui/screens/remove/RemoveFlow.tsx
index 7001fde27..696107486 100644
--- a/src/cli/tui/screens/remove/RemoveFlow.tsx
+++ b/src/cli/tui/screens/remove/RemoveFlow.tsx
@@ -331,7 +331,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'agent-success', agentName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-agent', agentName, preview: result.preview });
@@ -353,7 +353,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'gateway-success', gatewayName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-gateway', gatewayName, preview: result.preview });
@@ -375,7 +375,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'tool-success', toolName: tool.name });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-gateway-target', tool, preview: result.preview });
@@ -397,7 +397,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'memory-success', memoryName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-memory', memoryName, preview: result.preview });
@@ -419,7 +419,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'identity-success', identityName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-identity', identityName, preview: result.preview });
@@ -441,7 +441,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'evaluator-success', evaluatorName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-evaluator', evaluatorName, preview: result.preview });
@@ -463,7 +463,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'online-eval-success', configName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-online-eval', configName, preview: result.preview });
@@ -485,7 +485,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'policy-engine-success', engineName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-policy-engine', engineName, preview: result.preview });
@@ -510,7 +510,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'policy-success', policyName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-policy', compositeKey, policyName, preview: result.preview });
@@ -532,7 +532,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'config-bundle-success', bundleName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-config-bundle', bundleName, preview: result.preview });
@@ -554,7 +554,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'ab-test-success', testName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-ab-test', testName, preview: result.preview });
@@ -576,7 +576,7 @@ export function RemoveFlow({
           if (removeResult.success) {
             setFlow({ name: 'runtime-endpoint-success', endpointName });
           } else {
-            setFlow({ name: 'error', message: removeResult.error });
+            setFlow({ name: 'error', message: removeResult.error.message });
           }
         } else {
           setFlow({ name: 'confirm-runtime-endpoint', endpointName, preview: result.preview });
@@ -662,7 +662,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'agent-success', agentName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -678,7 +678,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'gateway-success', gatewayName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -694,7 +694,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'tool-success', toolName: tool.name, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -710,7 +710,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'memory-success', memoryName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -726,7 +726,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'identity-success', identityName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -742,7 +742,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'evaluator-success', evaluatorName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -758,7 +758,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'online-eval-success', configName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -774,7 +774,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'policy-engine-success', engineName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -790,7 +790,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'policy-success', policyName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -806,7 +806,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'config-bundle-success', bundleName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -822,7 +822,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'ab-test-success', testName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
@@ -838,7 +838,7 @@ export function RemoveFlow({
       if (result.success) {
         pendingResultRef.current = { name: 'runtime-endpoint-success', endpointName, logFilePath: result.logFilePath };
       } else {
-        pendingResultRef.current = { name: 'error', message: result.error };
+        pendingResultRef.current = { name: 'error', message: result.error.message };
       }
       setResultReady(true);
     },
diff --git a/src/cli/tui/screens/run-eval/RunBatchEvalFlow.tsx b/src/cli/tui/screens/run-eval/RunBatchEvalFlow.tsx
index 38c03c150..36bb09ec4 100644
--- a/src/cli/tui/screens/run-eval/RunBatchEvalFlow.tsx
+++ b/src/cli/tui/screens/run-eval/RunBatchEvalFlow.tsx
@@ -260,7 +260,7 @@ export function RunBatchEvalFlow({ onExit }: RunBatchEvalFlowProps) {
           setFlow(prev => {
             if (prev.name !== 'running') return prev;
             const steps = prev.steps.map(s =>
-              s.status === 'running' ? { ...s, status: 'error' as const, error: result.error } : s
+              s.status === 'running' ? { ...s, status: 'error' as const, error: result.error.message } : s
             );
             return { ...prev, steps };
           });
@@ -268,7 +268,7 @@ export function RunBatchEvalFlow({ onExit }: RunBatchEvalFlowProps) {
           if (cancelled) return;
           setFlow({
             name: 'error',
-            message: result.error ?? 'Batch evaluation failed',
+            message: result.error.message ?? 'Batch evaluation failed',
             logFilePath: result.logFilePath,
           });
           return;
@@ -472,7 +472,7 @@ function BatchEvalWizard({ agents, evaluators: rawEvaluators, onComplete, onExit
         const region = targetRegion ?? detectedRegion;
         const agentResult = resolveAgent(context, { runtime: config.agent });
         if (!agentResult.success) {
-          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error });
+          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error.message });
           return;
         }
 
@@ -846,7 +846,7 @@ function ResultsView({ result, savedFilePath, onRunAnother, onExit }: ResultsVie
     isActive: true,
   });
 
-  const evalRes = result.evaluationResults;
+  const evalRes = result.success ? result.evaluationResults : undefined;
   const summaries = evalRes?.evaluatorSummaries;
 
   // Fall back to local grouping when API summaries aren't available
diff --git a/src/cli/tui/screens/run-eval/RunEvalFlow.tsx b/src/cli/tui/screens/run-eval/RunEvalFlow.tsx
index 6b4ced516..be9c94d08 100644
--- a/src/cli/tui/screens/run-eval/RunEvalFlow.tsx
+++ b/src/cli/tui/screens/run-eval/RunEvalFlow.tsx
@@ -20,7 +20,7 @@ type FlowState =
   | { name: 'loading' }
   | { name: 'wizard'; data: RunEvalFlowData }
   | { name: 'running'; config: RunEvalConfig }
-  | { name: 'results'; result: RunEvalResult; run: EvalRunResult }
+  | { name: 'results'; result: Extract<RunEvalResult, { success: true }>; run: EvalRunResult }
   | { name: 'creds-error'; message: string }
   | { name: 'error'; message: string };
 
@@ -146,11 +146,11 @@ export function RunEvalFlow({ onExit, onViewRuns }: RunEvalFlowProps) {
         if (cancelled) return;
 
         if (!result.success || !result.run) {
-          setFlow({ name: 'error', message: result.error ?? 'Evaluation failed' });
+          setFlow({ name: 'error', message: !result.success ? result.error.message : 'Evaluation failed' });
           return;
         }
 
-        setFlow({ name: 'results', result, run: result.run });
+        setFlow({ name: 'results', result: result, run: result.run });
       } catch (err) {
         if (!cancelled) setFlow({ name: 'error', message: getErrorMessage(err) });
       }
diff --git a/src/cli/tui/screens/run-eval/RunEvalScreen.tsx b/src/cli/tui/screens/run-eval/RunEvalScreen.tsx
index d98a7431c..aee0a4142 100644
--- a/src/cli/tui/screens/run-eval/RunEvalScreen.tsx
+++ b/src/cli/tui/screens/run-eval/RunEvalScreen.tsx
@@ -84,7 +84,7 @@ export function RunEvalScreen({ agents, evaluatorItems: rawEvaluatorItems, onCom
         const { region } = await detectRegion();
         const agentResult = resolveAgent(context, { runtime: wizard.config.agent });
         if (!agentResult.success) {
-          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error });
+          if (!cancelled) setSessionResult({ key: fetchKey, phase: 'error', message: agentResult.error.message });
           return;
         }
 
diff --git a/src/cli/tui/screens/runtime-endpoint/AddRuntimeEndpointFlow.tsx b/src/cli/tui/screens/runtime-endpoint/AddRuntimeEndpointFlow.tsx
index 83bda78e5..18c482e35 100644
--- a/src/cli/tui/screens/runtime-endpoint/AddRuntimeEndpointFlow.tsx
+++ b/src/cli/tui/screens/runtime-endpoint/AddRuntimeEndpointFlow.tsx
@@ -95,7 +95,7 @@ export function AddRuntimeEndpointFlow({
         });
         return;
       }
-      setFlow({ name: 'error', message: result.error ?? 'Unknown error' });
+      setFlow({ name: 'error', message: result.error?.message ?? 'Unknown error' });
     });
   }, []);
 
diff --git a/src/cli/tui/screens/status/useStatusFlow.ts b/src/cli/tui/screens/status/useStatusFlow.ts
index 2260e1e82..4861a9b0a 100644
--- a/src/cli/tui/screens/status/useStatusFlow.ts
+++ b/src/cli/tui/screens/status/useStatusFlow.ts
@@ -99,7 +99,7 @@ export function useStatusFlow() {
           ...prev,
           phase: 'ready',
           statusesLoaded: true,
-          statusesError: result.error,
+          statusesError: result.error.message,
         }));
         return;
       }
diff --git a/src/lib/index.ts b/src/lib/index.ts
index cab20d720..4cc958d04 100644
--- a/src/lib/index.ts
+++ b/src/lib/index.ts
@@ -25,5 +25,8 @@ export * from './errors';
 export * from './packaging';
 export * from './utils';
 
+// Types
+export type { Result } from './types';
+
 // Schema I/O utilities
 export * from './schemas/io';
diff --git a/src/lib/types.ts b/src/lib/types.ts
new file mode 100644
index 000000000..2c776e1fd
--- /dev/null
+++ b/src/lib/types.ts
@@ -0,0 +1,15 @@
+/**
+ * Discriminated union for fallible operations, inspired by Rust's Result<T, E>.
+ *
+ * Success branch spreads T onto the result; failure branch carries an Error.
+ * E extends Error so callers always get stack traces, cause chains, and instanceof narrowing.
+ *
+ * @example
+ *   Result                                    // { success: true } | { success: false; error: Error }
+ *   Result<{ name: string }>                  // { success: true; name: string } | { success: false; error: Error }
+ *   Result<{ name: string }, ValidationError> // { success: true; name: string } | { success: false; error: ValidationError }
+ */
+// eslint-disable-next-line @typescript-eslint/no-empty-object-type
+export type Result<T extends Record<string, unknown> = {}, E extends Error = Error> =
+  | ({ success: true } & T)
+  | { success: false; error: E };