fix(server): tell multi-repo agents which repos are in the project

apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts

@@ -916,6 +916,90 @@ describe("ProviderCommandReactor", () => {
         expect(multiCall?.[1]).toMatchObject({
           cwd: "/tmp/multi-workspace",
           additionalRoots: ["/tmp/multi-workspace/backend", "/tmp/oss/frontend"],
+          repoRoots: ["/tmp/multi-workspace/backend", "/tmp/oss/frontend"],
+        });
+      }),
+  );
+
+  effectIt.effect(
+    "launches a multi-repo worktree run with every worktree, including the anchor",
+    () =>
+      Effect.gen(function* () {
+        const harness = yield* Effect.promise(() => createHarness());
+        const now = "2026-01-01T00:00:00.000Z";
+        const multiModelSelection = {
+          instanceId: ProviderInstanceId.make("codex"),
+          model: "gpt-5-codex",
+        };
+
+        yield* harness.engine.dispatch({
+          type: "project.create",
+          commandId: CommandId.make("cmd-project-create-multi-wt"),
+          projectId: asProjectId("project-multi-wt"),
+          title: "Multi Repo Project",
+          workspaceRoot: "/tmp/multi-workspace",
+          repoRoots: ["/tmp/multi-workspace/backend", "/tmp/oss/frontend"],
+          defaultModelSelection: multiModelSelection,
+          createdAt: now,
+        });
+        yield* harness.engine.dispatch({
+          type: "thread.create",
+          commandId: CommandId.make("cmd-thread-create-multi-wt"),
+          threadId: ThreadId.make("thread-multi-wt"),
+          projectId: asProjectId("project-multi-wt"),
+          title: "Multi Worktree Thread",
+          modelSelection: multiModelSelection,
+          interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+          runtimeMode: "approval-required",
+          branch: "t3code/multi",
+          worktreePath: "/tmp/worktrees/thread-multi-wt/backend",
+          worktrees: [
+            {
+              repoRoot: "/tmp/multi-workspace/backend",
+              worktreePath: "/tmp/worktrees/thread-multi-wt/backend",
+            },
+            {
+              repoRoot: "/tmp/oss/frontend",
+              worktreePath: "/tmp/worktrees/thread-multi-wt/frontend",
+            },
+          ],
+          createdAt: now,
+        });
+
+        yield* harness.engine.dispatch({
+          type: "thread.turn.start",
+          commandId: CommandId.make("cmd-turn-start-multi-wt"),
+          threadId: ThreadId.make("thread-multi-wt"),
+          message: {
+            messageId: asMessageId("user-message-multi-wt"),
+            role: "user",
+            text: "edit both repos",
+            attachments: [],
+          },
+          interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+          runtimeMode: "approval-required",
+          createdAt: now,
+        });
+
+        yield* Effect.promise(() =>
+          waitFor(() =>
+            harness.startSession.mock.calls.some(
+              (call) => call[0] === ThreadId.make("thread-multi-wt"),
+            ),
+          ),
+        );
+        const call = harness.startSession.mock.calls.find(
+          (entry) => entry[0] === ThreadId.make("thread-multi-wt"),
+        );
+        // The session anchors in the first worktree, so `additionalRoots`
+        // leaves it out while `repoRoots` keeps it.
+        expect(call?.[1]).toMatchObject({
+          cwd: "/tmp/worktrees/thread-multi-wt/backend",
+          additionalRoots: ["/tmp/worktrees/thread-multi-wt/frontend"],
+          repoRoots: [
+            "/tmp/worktrees/thread-multi-wt/backend",
+            "/tmp/worktrees/thread-multi-wt/frontend",
+          ],
         });
       }),
   );

apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

@@ -725,6 +725,8 @@ const make = Effect.gen(function* () {
         projects: project ? [project] : [],
       });
     const additionalRoots = manifest ? manifestExtraRoots(manifest) : [];
+    const repoRoots =
+      manifest && additionalRoots.length > 0 ? manifest.roots.map((root) => root.path) : [];
     const refreshWorkspaceSnapshot = effectiveCwd
       ? providerRegistry
           .refreshWorkspaceSnapshot({ instanceId: desiredInstanceId, cwd: effectiveCwd })
@@ -752,6 +754,7 @@ const make = Effect.gen(function* () {
           ...(effectiveCwd ? { cwd: effectiveCwd } : {}),
           ...(sessionTitle ? { title: sessionTitle } : {}),
           ...(additionalRoots.length > 0 ? { additionalRoots } : {}),
+          ...(repoRoots.length > 0 ? { repoRoots } : {}),
           modelSelection: desiredModelSelection,
           ...(input?.resumeCursor !== undefined ? { resumeCursor: input.resumeCursor } : {}),
           runtimeMode: desiredRuntimeMode,

apps/server/src/provider/CodexDeveloperInstructions.ts

@@ -1,6 +1,6 @@
 import type { ProviderInteractionMode } from "@t3tools/contracts";
 import type { V2TurnStartParams__AdditionalContextEntry } from "effect-codex-app-server/schema";
-import { buildRuntimeInstructions } from "./RuntimeInstructions.ts";
+import { buildRuntimeInstructions, type MultiRepoWorkspace } from "./RuntimeInstructions.ts";
 
 const T3_CODE_BROWSER_TOOL_INSTRUCTIONS = `## T3 Code collaborative browser
 
@@ -188,7 +188,7 @@ export interface CodexRuntimeInfo {
   readonly model: string;
   readonly modelName?: string | undefined;
   readonly reasoningEffort: string;
-  readonly multiRepo?: boolean | undefined;
+  readonly multiRepo?: MultiRepoWorkspace | undefined;
 }
 
 /** Mode prompt for `turn/start.collaborationMode.settings.developer_instructions`. */

apps/server/src/provider/Layers/AntigravityAdapter.ts

@@ -36,7 +36,11 @@ import * as EffectAcpErrors from "effect-acp/errors";
 import type * as EffectAcpSchema from "effect-acp/schema";
 
 import { ServerConfig } from "../../config.ts";
-import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
+import {
+  buildRuntimeInstructions,
+  multiRepoWorkspace,
+  type MultiRepoWorkspace,
+} from "../RuntimeInstructions.ts";
 import * as McpProviderSession from "../../mcp/McpProviderSession.ts";
 import type { AntigravityAuth } from "../AntigravityAuth.ts";
 import {
@@ -192,8 +196,8 @@ interface TurnIntent {
 interface SessionContext {
   readonly threadId: ThreadId;
   readonly cwd: string;
-  /** The session spans several repository roots. */
-  readonly multiRepo: boolean;
+  /** Set when the session has roots beyond its working directory. */
+  readonly multiRepo: MultiRepoWorkspace | undefined;
   readonly nativeSessionId: string;
   readonly scope: Scope.Closeable;
   readonly runtime: Runtime;
@@ -867,7 +871,7 @@ export const makeAntigravityAdapter = Effect.fn("makeAntigravityAdapter")(functi
               context = {
                 threadId: input.threadId,
                 cwd,
-                multiRepo: (input.additionalRoots?.length ?? 0) > 0,
+                multiRepo: multiRepoWorkspace(input),
                 nativeSessionId: started.sessionId,
                 scope: sessionScope,
                 runtime,

apps/server/src/provider/Layers/ClaudeAdapter.test.ts

@@ -471,13 +471,17 @@ describe("ClaudeAdapterLive", () => {
         provider: ProviderDriverKind.make("claudeAgent"),
         cwd: "/workspace",
         additionalRoots: ["/workspace/api", "/workspace/web"],
+        repoRoots: ["/workspace/api", "/workspace/web"],
         runtimeMode: "full-access",
       });
 
       assert.deepEqual(harness.getLastCreateQueryInput()?.options.systemPrompt, {
         type: "preset",
         preset: "claude_code",
-        append: buildRuntimeInstructions({ harness: "Claude Code", multiRepo: true }),
+        append: buildRuntimeInstructions({
+          harness: "Claude Code",
+          multiRepo: { cwd: "/workspace", repoRoots: ["/workspace/api", "/workspace/web"] },
+        }),
       });
     }).pipe(
       Effect.provideService(Random.Random, makeDeterministicRandomService()),

apps/server/src/provider/Layers/ClaudeAdapter.ts

@@ -93,7 +93,7 @@ import { resolveClaudeSdkExecutablePath } from "../Drivers/ClaudeExecutable.ts";
 import { claudeSignedOutMessage, makeClaudeEnvironment } from "../Drivers/ClaudeHome.ts";
 import { planClaudeSkillDispatch } from "../Drivers/ClaudeSkillDispatch.ts";
 import { discoverClaudeSkills } from "../Drivers/ClaudeSkills.ts";
-import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
+import { buildRuntimeInstructions, multiRepoWorkspace } from "../RuntimeInstructions.ts";
 import {
   BUNDLED_CLAUDE_MODEL_CATALOG,
   type ClaudeModelCatalog,
@@ -4915,7 +4915,7 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
           // Model and effort can change after this session-level prompt is set.
           append: buildRuntimeInstructions({
             harness: "Claude Code",
-            multiRepo: (input.additionalRoots?.length ?? 0) > 0,
+            multiRepo: multiRepoWorkspace(input),
           }),
         },
         settingSources: [...CLAUDE_SETTING_SOURCES],

apps/server/src/provider/Layers/CodexAdapter.ts

@@ -2282,6 +2282,7 @@ export const makeCodexAdapter = Effect.fn("makeCodexAdapter")(function* (
           ...(input.additionalRoots && input.additionalRoots.length > 0
             ? { additionalRoots: input.additionalRoots }
             : {}),
+          ...(input.repoRoots && input.repoRoots.length > 0 ? { repoRoots: input.repoRoots } : {}),
           binaryPath: codexConfig.binaryPath,
           ...(options?.models ? { models: options.models } : {}),
           launchArgs: resolveCodexLaunchArgs(codexConfig.launchArgs, options?.environment),

apps/server/src/provider/Layers/CodexSessionRuntime.test.ts

@@ -13,6 +13,7 @@ import {
   buildCodexAdditionalContext,
   buildCodexDeveloperInstructions,
 } from "../CodexDeveloperInstructions.ts";
+import type { MultiRepoWorkspace } from "../RuntimeInstructions.ts";
 import { codexSessionAppServerArgs } from "./codexLaunchArgs.ts";
 import {
   buildTurnStartParams,
@@ -297,7 +298,7 @@ describe("buildTurnStartParams", () => {
 
   it.effect("asks a multi-repo session for absolute file paths", () =>
     Effect.gen(function* () {
-      const instructions = function* (multiRepo: boolean) {
+      const instructions = function* (multiRepo: MultiRepoWorkspace | undefined) {
         const params = yield* buildTurnStartParams({
           threadId: "provider-thread-1",
           runtimeMode: "full-access",
@@ -308,8 +309,13 @@ describe("buildTurnStartParams", () => {
         return params.additionalContext?.t3_code_runtime?.value ?? "";
       };
 
-      NodeAssert.match(yield* instructions(true), /<multi_repo_workspace>/);
-      NodeAssert.doesNotMatch(yield* instructions(false), /<multi_repo_workspace>/);
+      const multiRepo = yield* instructions({
+        cwd: "/work",
+        repoRoots: ["/work/api", "/work/web"],
+      });
+      NodeAssert.match(multiRepo, /<multi_repo_workspace>/);
+      NodeAssert.match(multiRepo, /- \/work\/api\n- \/work\/web/);
+      NodeAssert.doesNotMatch(yield* instructions(undefined), /<multi_repo_workspace>/);
     }),
   );
 

apps/server/src/provider/Layers/CodexSessionRuntime.ts

@@ -45,6 +45,7 @@ import {
   buildCodexDeveloperInstructions,
   type T3CodeToolAvailability,
 } from "../CodexDeveloperInstructions.ts";
+import { multiRepoWorkspace, type MultiRepoWorkspace } from "../RuntimeInstructions.ts";
 const decodeV2TurnStartResponse = Schema.decodeUnknownEffect(EffectCodexSchema.V2TurnStartResponse);
 
 const PROVIDER = ProviderDriverKind.make("codex");
@@ -183,6 +184,8 @@ export interface CodexSessionRuntimeOptions {
    * registered after thread open via `skills/extraRoots/set`.
    */
   readonly additionalRoots?: ReadonlyArray<string>;
+  /** Every repo root the session works in, including `cwd` when it is one. */
+  readonly repoRoots?: ReadonlyArray<string>;
   readonly runtimeMode: RuntimeMode;
   readonly model?: string;
   readonly serviceTier?: CodexServiceTier | undefined;
@@ -597,7 +600,7 @@ function buildCodexTurnInstructions(input: {
   readonly modelName?: string;
   readonly effort?: EffectCodexSchema.V2TurnStartParams__ReasoningEffort;
   readonly browserToolsAvailable?: boolean | T3CodeToolAvailability;
-  readonly multiRepo?: boolean;
+  readonly multiRepo?: MultiRepoWorkspace | undefined;
 }): Pick<CodexTurnStartParamsWithCollaborationMode, "collaborationMode" | "additionalContext"> {
   if (input.interactionMode === undefined) {
     return {};
@@ -640,8 +643,8 @@ export function buildTurnStartParams(input: {
   readonly interactionMode?: ProviderInteractionMode;
   /** Defaults to true so callers that predate the agent-access gate are unchanged. */
   readonly browserToolsAvailable?: boolean | T3CodeToolAvailability;
-  /** The session spans several repository roots. */
-  readonly multiRepo?: boolean;
+  /** Set when the session has roots beyond its working directory. */
+  readonly multiRepo?: MultiRepoWorkspace | undefined;
 }): Effect.Effect<
   CodexTurnStartParamsWithCollaborationMode,
   CodexErrors.CodexAppServerProtocolParseError
@@ -664,7 +667,7 @@ export function buildTurnStartParams(input: {
     ...(input.modelName ? { modelName: input.modelName } : {}),
     ...(input.effort ? { effort: input.effort } : {}),
     browserToolsAvailable: input.browserToolsAvailable ?? true,
-    ...(input.multiRepo ? { multiRepo: true } : {}),
+    ...(input.multiRepo ? { multiRepo: input.multiRepo } : {}),
   });
 
   return decodeCodexTurnStartParamsWithCollaborationMode({
@@ -2608,7 +2611,7 @@ export const makeCodexSessionRuntime = (
               options.appServerArgs,
               options.mcpCapabilities,
             ),
-            multiRepo: (options.additionalRoots?.length ?? 0) > 0,
+            multiRepo: multiRepoWorkspace(options),
           });
           yield* Ref.set(lastAdditionalContextRef, params.additionalContext);
           const rawResponse = yield* client.raw.request("turn/start", params);

apps/server/src/provider/Layers/CursorAdapter.ts

@@ -42,7 +42,11 @@ import type * as EffectAcpSchema from "effect-acp/schema";
 
 import { resolveAttachmentPath } from "../../attachmentStore.ts";
 import { ServerConfig } from "../../config.ts";
-import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
+import {
+  buildRuntimeInstructions,
+  multiRepoWorkspace,
+  type MultiRepoWorkspace,
+} from "../RuntimeInstructions.ts";
 import * as McpProviderSession from "../../mcp/McpProviderSession.ts";
 import {
   ProviderAdapterProcessError,
@@ -138,8 +142,8 @@ interface CursorSessionContext {
   session: ProviderSession;
   readonly scope: Scope.Closeable;
   readonly acp: AcpSessionRuntime.AcpSessionRuntime["Service"];
-  /** The session spans several repository roots. */
-  readonly multiRepo: boolean;
+  /** Set when the session has roots beyond its working directory. */
+  readonly multiRepo: MultiRepoWorkspace | undefined;
   notificationFiber: Fiber.Fiber<void, never> | undefined;
   readonly pendingApprovals: Map<ApprovalRequestId, PendingApproval>;
   readonly pendingUserInputs: Map<ApprovalRequestId, PendingUserInput>;
@@ -795,7 +799,7 @@ export function makeCursorAdapter(
             session,
             scope: sessionScope,
             acp,
-            multiRepo: (input.additionalRoots?.length ?? 0) > 0,
+            multiRepo: multiRepoWorkspace(input),
             notificationFiber: undefined,
             pendingApprovals,
             pendingUserInputs,

apps/server/src/provider/Layers/GrokAdapter.ts

@@ -40,7 +40,11 @@ import type * as EffectAcpSchema from "effect-acp/schema";
 
 import { resolveAttachmentPath } from "../../attachmentStore.ts";
 import { ServerConfig } from "../../config.ts";
-import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
+import {
+  buildRuntimeInstructions,
+  multiRepoWorkspace,
+  type MultiRepoWorkspace,
+} from "../RuntimeInstructions.ts";
 import * as McpProviderSession from "../../mcp/McpProviderSession.ts";
 import {
   ProviderAdapterProcessError,
@@ -138,8 +142,8 @@ interface GrokSessionContext {
   session: ProviderSession;
   readonly scope: Scope.Closeable;
   readonly acp: AcpSessionRuntime.AcpSessionRuntime["Service"];
-  /** The session spans several repository roots. */
-  readonly multiRepo: boolean;
+  /** Set when the session has roots beyond its working directory. */
+  readonly multiRepo: MultiRepoWorkspace | undefined;
   notificationFiber: Fiber.Fiber<void, never> | undefined;
   readonly pendingApprovals: Map<ApprovalRequestId, PendingApproval>;
   readonly pendingUserInputs: Map<ApprovalRequestId, PendingUserInput>;
@@ -1292,7 +1296,7 @@ export function makeGrokAdapter(grokSettings: GrokSettings, options?: GrokAdapte
             session,
             scope: sessionScope,
             acp,
-            multiRepo: (input.additionalRoots?.length ?? 0) > 0,
+            multiRepo: multiRepoWorkspace(input),
             notificationFiber: undefined,
             pendingApprovals,
             pendingUserInputs,

apps/server/src/provider/Layers/OpenCodeAdapter.ts

@@ -43,7 +43,11 @@ import {
   ProviderAdapterSessionNotFoundError,
   ProviderAdapterValidationError,
 } from "../Errors.ts";
-import { buildRuntimeInstructions } from "../RuntimeInstructions.ts";
+import {
+  buildRuntimeInstructions,
+  multiRepoWorkspace,
+  type MultiRepoWorkspace,
+} from "../RuntimeInstructions.ts";
 import { type OpenCodeAdapterShape } from "../Services/OpenCodeAdapter.ts";
 import {
   buildOpenCodePermissionRules,
@@ -341,8 +345,8 @@ interface OpenCodeSessionContext {
   readonly client: OpencodeClient;
   readonly server: OpenCodeServerConnection;
   readonly directory: string;
-  /** The session spans several repository roots. */
-  readonly multiRepo: boolean;
+  /** Set when the session has roots beyond its working directory. */
+  readonly multiRepo: MultiRepoWorkspace | undefined;
   openCodeSessionId: string;
   readonly relatedSessionIds: Set<string>;
   readonly resolvedRequestIds: Set<string>;
@@ -3010,7 +3014,7 @@ export function makeOpenCodeAdapter(
           client: started.client,
           server: started.server,
           directory,
-          multiRepo: (input.additionalRoots?.length ?? 0) > 0,
+          multiRepo: multiRepoWorkspace(input),
           openCodeSessionId: started.openCodeSession.id,
           relatedSessionIds: new Set([started.openCodeSession.id]),
           resolvedRequestIds: new Set(),