diff --git a/server/services/agentLifecycle.postureGate.test.js b/server/services/agentLifecycle.postureGate.test.js
new file mode 100644
index 0000000000..8d6eb04cd5
--- /dev/null
+++ b/server/services/agentLifecycle.postureGate.test.js
@@ -0,0 +1,173 @@
+/**
+ * The spawn-time public-review posture gate, driven through `spawnAgentForTask`.
+ *
+ * Deliberately a BEHAVIORAL test, not a source scrape. #5830 collapsed the two
+ * per-stage gates into one posture check and dropped the `publicReview &&`
+ * condition guarding them (fixed in #5866). An
+ * ordinary task's execution profile maps to a `null` posture, and
+ * `supportsPublicReviewPosture(provider, null)` is false for EVERY provider —
+ * so the gate fired on every spawn and blocked every CoS agent on the install
+ * with "has no enforced null public-content review mode".
+ *
+ * Neither the guard that existed at the time nor the one #5866 added can see
+ * that: agentLifecycle.test.js reads the orchestrator as a STRING, so it pins
+ * only that the call site NAMES `publicReviewProviderBlock`. A dropped
+ * condition is invisible to a grep — and so is a bare
+ * `supportsPublicReviewPosture` block reintroduced next to it tomorrow, which
+ * would blank every install again with CI green. So the observing surface here
+ * is the spawn itself. The ordinary-task cases below fail against the broken
+ * revision and pass against the fix; the last one pins that the gate still
+ * fails closed for a stage that actually requested a posture, so the suite
+ * cannot be satisfied by simply deleting the gate.
+ *
+ * Mirrors the mock set in agentLifecycle.spawnViaRunner.test.js — the leaves are
+ * stubbed so the real orchestrator runs.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+vi.mock('./cosRunnerClient.js', async (importOriginal) => ({
+  ...(await importOriginal()),
+  spawnAgentViaRunner: vi.fn(),
+  getRunnerHealth: vi.fn().mockResolvedValue({ available: true, uptime: 3600 }),
+}));
+vi.mock('./cosAgentLifecycle.js', () => ({
+  registerAgent: vi.fn().mockResolvedValue(undefined),
+  updateAgent: vi.fn().mockResolvedValue(undefined),
+  completeAgent: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock('./agentRunTracking.js', () => ({
+  createAgentRun: vi.fn().mockResolvedValue(undefined),
+  completeAgentRun: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock('./agentFinalization.js', () => ({
+  dispatchRecoveredTaskOutputHook: vi.fn().mockResolvedValue(undefined),
+  finalizeAgent: vi.fn().mockResolvedValue(undefined),
+  releaseAgentLane: vi.fn(),
+  stampLiExecutionVerdict: vi.fn(async (update) => update),
+}));
+vi.mock('./cosEvents.js', () => ({
+  emitLog: vi.fn(),
+  cosEvents: { emit: vi.fn(), on: vi.fn() },
+}));
+vi.mock('./cos.js', () => ({
+  getConfig: vi.fn().mockResolvedValue({}),
+  updateTask: vi.fn().mockResolvedValue(undefined),
+  getTaskById: vi.fn().mockResolvedValue(null),
+  getAgentRecord: vi.fn().mockResolvedValue(null),
+}));
+vi.mock('./git.js', () => ({ resolveForgeTokenEnv: vi.fn().mockResolvedValue({}) }));
+vi.mock('./agentCliSpawning.js', () => ({
+  buildCliSpawnConfig: vi.fn(),
+  isClaudeCliProvider: vi.fn().mockReturnValue(false),
+  isTuiProvider: vi.fn().mockReturnValue(true),
+  getClaudeSettingsEnv: vi.fn().mockResolvedValue({}),
+  spawnDirectly: vi.fn(),
+}));
+vi.mock('./agentTuiSpawning.js', () => ({
+  buildTuiSpawnConfig: vi.fn(),
+  spawnTuiAgent: vi.fn(),
+}));
+vi.mock('./agentProviderResolution.js', () => ({ resolveAgentProviderAndModel: vi.fn() }));
+// Stops the spawn immediately AFTER the posture gate — the gate is what this
+// file observes, and letting the real workspace prep run would touch git.
+vi.mock('./agentWorkspacePrep.js', () => ({
+  prepareAgentWorkspace: vi.fn().mockResolvedValue({ outcome: 'blocked', reason: 'stop here' }),
+}));
+vi.mock('./agentWorktreeCleanup.js', () => ({
+  cleanupAgentWorktree: vi.fn(),
+  releaseRetryHold: vi.fn().mockResolvedValue({}),
+}));
+vi.mock('./agentCompletionCleanup.js', () => ({ runAgentCompletionCleanup: vi.fn() }));
+vi.mock('./agentSummaryExtraction.js', () => ({ extractFinalSummary: vi.fn() }));
+vi.mock('./agentManagement.js', () => ({ handleOrphanedTask: vi.fn() }));
+vi.mock('./agentRunEventLog.js', () => ({ appendRunEvent: vi.fn(async () => ({ appended: true })) }));
+vi.mock('./agentPromptBuilder.js', () => ({ buildAgentPrompt: vi.fn(), getAppWorkspace: vi.fn() }));
+vi.mock('./agentErrorAnalysis.js', () => ({
+  analyzeAgentFailure: vi.fn().mockReturnValue({ category: 'startup-failure', actionable: false }),
+}));
+vi.mock('./appActivity.js', () => ({ releaseAppReviewMarker: vi.fn().mockResolvedValue(undefined) }));
+vi.mock('./instances.js', () => ({ ensureInstanceId: vi.fn().mockResolvedValue('instance-1') }));
+vi.mock('./toolStateMachine.js', () => ({
+  createToolExecution: vi.fn(() => ({ id: 'exec-1' })),
+  startExecution: vi.fn(),
+  completeExecution: vi.fn(),
+  errorExecution: vi.fn(),
+}));
+vi.mock('./executionLanes.js', () => ({
+  determineLane: vi.fn(() => 'standard'),
+  acquire: vi.fn(() => ({ success: true })),
+  release: vi.fn(),
+}));
+vi.mock('./updateChecker.js', () => ({ isUpdateInProgress: vi.fn().mockReturnValue(false) }));
+vi.mock('./modelAbuseGuard.js', () => ({
+  materializePublicReviewInput: vi.fn(),
+  materializePublicReviewPatches: vi.fn(),
+  readPublicReviewInputSnapshot: vi.fn(),
+  validatePublicReviewModel: vi.fn().mockResolvedValue({ ok: true }),
+}));
+
+import { spawnAgentForTask } from './agentLifecycle.js';
+import { resolveAgentProviderAndModel } from './agentProviderResolution.js';
+import { updateTask } from './cos.js';
+import { spawningTasks, runnerAgents } from './agentState.js';
+
+// The provider every install actually runs its CoS agents on, and the one named
+// in the #5866 outage: a TUI session has no maintained public-review recipe, so
+// it is exactly the provider the broken gate rejected for ordinary work.
+const CLAUDE_TUI = { id: 'claude-code-tui', type: 'tui', command: 'claude', envVars: {} };
+
+/** Every `updateTask` call that wrote a public-review posture block. */
+const postureBlockWrites = () => vi.mocked(updateTask).mock.calls.filter(
+  ([, update]) => typeof update?.metadata?.blockedReason === 'string'
+    && update.metadata.blockedReason.includes('public-content review mode'),
+);
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  spawningTasks.clear();
+  runnerAgents.clear();
+  vi.mocked(resolveAgentProviderAndModel).mockResolvedValue({
+    ok: true, provider: CLAUDE_TUI, selectedModel: 'sonnet', modelSelection: {},
+  });
+});
+
+describe('public-review posture gate — spawn behavior (#5866)', () => {
+  // THE regression. An ordinary task declares no execution profile, so it
+  // requests no posture and the gate must not fire. When it did, every CoS
+  // agent — user tasks and scheduled tasks alike — was blocked on arrival.
+  it('does not block an ordinary task, which requests no posture', async () => {
+    await spawnAgentForTask({ id: 'task-ordinary', metadata: {} });
+
+    expect(postureBlockWrites()).toEqual([]);
+  });
+
+  it('does not block an ordinary task that carries unrelated metadata', async () => {
+    await spawnAgentForTask({ id: 'task-plain', taskType: 'user', metadata: { app: 'portos-default' } });
+
+    expect(postureBlockWrites()).toEqual([]);
+  });
+
+  // The other half of the contract: a stage that DID request a posture still
+  // fails closed on a provider with no maintained recipe. A fix for the above
+  // that simply deleted the gate would pass every test but this one.
+  it('still blocks a public-review stage whose provider has no enforced posture', async () => {
+    await spawnAgentForTask({
+      id: 'task-public-review',
+      metadata: {
+        executionProfile: 'public-review-gate',
+        // The scan gate runs first and would block on its own; clear it so the
+        // posture gate is what this case actually reaches.
+        pipeline: { securityScan: { completed: true, status: 'passed', safePrCount: 1 } },
+      },
+    });
+
+    const [call] = postureBlockWrites();
+    expect(call).toBeDefined();
+    const [, update] = call;
+    expect(update.status).toBe('blocked');
+    expect(update.metadata.blockedReason).toContain("Provider 'claude-code-tui'");
+    expect(update.metadata.blockedReason).toContain('no-tool');
+    expect(update.metadata.blockedCategory).toBe('public-review-provider-unsupported');
+  });
+});
diff --git a/server/services/modelAbuseGuard.js b/server/services/modelAbuseGuard.js
index 146ff27e3f..2088d1d246 100644
--- a/server/services/modelAbuseGuard.js
+++ b/server/services/modelAbuseGuard.js
@@ -37,7 +37,7 @@ import {
 } from '../lib/modelAbuseGuard.js';
 import { findCachedRepoFiles } from '../lib/hfCache.js';
 import { localRuntimeForProvider } from '../lib/localProviderRuntime.js';
-import { supportsPublicReviewPosture, PUBLIC_REVIEW_NO_TOOL_POSTURE } from '../lib/providerVendors.js';
+import { publicReviewProviderBlock, PUBLIC_REVIEW_NO_TOOL_POSTURE } from '../lib/providerVendors.js';
 import { withSpawnCwdEnv } from '../lib/spawnCwd.js';
 import { detectVenvBasePythonSync, createVenv, installPackages } from '../lib/pythonSetup.js';
 import { safeChildProcessOptions } from '../lib/processEnv.js';
@@ -156,9 +156,14 @@ function normalizePublicReviewInputs(pullRequests) {
  * their own model (grok, antigravity) legitimately run with no `--model` pin.
  */
 export async function validatePublicReviewModel({ provider, model, posture = PUBLIC_REVIEW_NO_TOOL_POSTURE } = {}) {
-  if (!supportsPublicReviewPosture(provider, posture)) {
-    return publicReviewModelFailure('public-review-provider-unsupported');
-  }
+  // Reuse the gate's own descriptor rather than re-deriving it. This takes a
+  // `posture` but hardcoded the NO-TOOL category, so a sandboxed-actions
+  // failure reported `public-review-provider-unsupported` for every provider.
+  // Latent today (the one caller passes the no-tool literal), but it fails
+  // closed with a plausible-looking wrong code, which is harder to diagnose
+  // than the outage #5866 fixed.
+  const postureBlock = publicReviewProviderBlock(provider, posture);
+  if (postureBlock) return publicReviewModelFailure(postureBlock.category);
   const modelId = typeof model === 'string' ? model.trim() : '';
   const runtime = localRuntimeForProvider(provider);
   if (!runtime) return { ok: true, model: modelId || null, runtime: null };
diff --git a/server/services/modelAbuseGuard.test.js b/server/services/modelAbuseGuard.test.js
index c2684c1c17..5e38a77e30 100644
--- a/server/services/modelAbuseGuard.test.js
+++ b/server/services/modelAbuseGuard.test.js
@@ -58,7 +58,7 @@ describe('validatePublicReviewModel', () => {
       provider: LOCAL_CLAUDE,
       model: 'safe-model',
       posture: 'sandboxed-actions',
-    })).resolves.toMatchObject({ ok: false, code: 'public-review-provider-unsupported' });
+    })).resolves.toMatchObject({ ok: false, code: 'public-review-actions-provider-unsupported' });
   });
 
   it('rejects missing model selection and an unavailable catalog', async () => {