diff --git a/api/server/controllers/agents/__tests__/resume.spec.js b/api/server/controllers/agents/__tests__/resume.spec.js
index 034c53189e..c38fa9cc9d 100644
--- a/api/server/controllers/agents/__tests__/resume.spec.js
+++ b/api/server/controllers/agents/__tests__/resume.spec.js
@@ -392,6 +392,82 @@ describe('ResumeAgentController (POST /agents/chat/resume)', () => {
       expect(mockGenerationJobManager.approvals.resolve).not.toHaveBeenCalled();
     });
 
+    // `abortJob` reports `success: false` with a REASON on every failure path. Gating on
+    // the absence of a reason treated an unreached job and a replacement generation as
+    // confirmed stops, settling the occurrence and pruning a checkpoint on neither.
+    it.each([
+      ['the job vanished before the abort landed', 'job_not_found'],
+      ['a replacement generation owns the conversation', 'generation_replaced'],
+      ['the generation is still live', 'job_still_active'],
+    ])('refuses to settle or prune when %s', async (_label, failureReason) => {
+      mockGenerationJobManager.getJob.mockResolvedValue(makeScheduledJob());
+      mockIsScheduleLive.mockResolvedValue(false);
+      mockGenerationJobManager.abortJob.mockResolvedValue({ success: false, failureReason });
+
+      const res = await post(approveBody());
+
+      expect(res.status).toBe(503);
+      expect(res.headers['retry-after']).toBe('1');
+      expect(res.body).toMatchObject({ code: 'SCHEDULE_STOP_UNCONFIRMED' });
+      expect(mockRecordScheduleOutcome).not.toHaveBeenCalled();
+      expect(mockDeleteAgentCheckpoint).not.toHaveBeenCalled();
+      expect(mockGenerationJobManager.approvals.resolve).not.toHaveBeenCalled();
+    });
+
+    // The exact regression: an abort that reported `success: false` and nothing else was
+    // read as a confirmed stop, so the occurrence was settled and its checkpoint pruned.
+    it('refuses to settle or prune on a bare unsuccessful abort with no reason', async () => {
+      mockGenerationJobManager.getJob.mockResolvedValue(makeScheduledJob());
+      mockIsScheduleLive.mockResolvedValue(false);
+      mockGenerationJobManager.abortJob.mockResolvedValue({ success: false });
+
+      const res = await post(approveBody());
+
+      expect(res.status).toBe(503);
+      expect(res.body).toMatchObject({ code: 'SCHEDULE_STOP_UNCONFIRMED' });
+      expect(mockRecordScheduleOutcome).not.toHaveBeenCalled();
+      expect(mockDeleteAgentCheckpoint).not.toHaveBeenCalled();
+    });
+
+    it('settles an occurrence whose generation was already terminal and drained', async () => {
+      mockGenerationJobManager.getJob.mockResolvedValue(makeScheduledJob());
+      mockIsScheduleLive.mockResolvedValue(false);
+      // No transition was needed, but `awaitProviderDrain` still proved the provider
+      // segment can no longer persist — a stop, just not one this call made. Refusing
+      // here would 503 a permanently terminal generation on every retry.
+      mockGenerationJobManager.abortJob.mockResolvedValue({
+        success: false,
+        failureReason: 'already_settled',
+      });
+
+      const res = await post(approveBody());
+
+      expect(res.status).toBe(409);
+      expect(res.body).toMatchObject({ code: 'SCHEDULE_NO_LONGER_ACTIVE' });
+      expect(mockRecordScheduleOutcome).toHaveBeenCalledWith(
+        expect.objectContaining({ scheduleId: 'schedule-1', status: 'interrupted' }),
+      );
+      expect(mockDeleteAgentCheckpoint).toHaveBeenCalled();
+    });
+
+    it('refuses to settle the stale resume handoff on an unconfirmed stop', async () => {
+      mockGenerationJobManager.getJob.mockResolvedValue(makeScheduledJob());
+      mockFinalizeScheduleResumeClaim.mockResolvedValue(false);
+      mockGenerationJobManager.abortJob.mockResolvedValue({
+        success: false,
+        failureReason: 'generation_replaced',
+      });
+
+      const res = await post(approveBody());
+
+      expect(res.status).toBe(503);
+      expect(res.headers['retry-after']).toBe('1');
+      expect(res.body).toMatchObject({ code: 'SCHEDULE_STOP_UNCONFIRMED' });
+      expect(mockRecordScheduleOutcome).not.toHaveBeenCalled();
+      expect(mockDeleteAgentCheckpoint).not.toHaveBeenCalled();
+      expect(mockInitializeClient).not.toHaveBeenCalled();
+    });
+
     it('records success after resumed persistence and before terminal publication', async () => {
       mockGenerationJobManager.getJob.mockResolvedValue(makeScheduledJob());
 
diff --git a/api/server/controllers/agents/resume.js b/api/server/controllers/agents/resume.js
index e4eb76e295..ea14afcb0e 100644
--- a/api/server/controllers/agents/resume.js
+++ b/api/server/controllers/agents/resume.js
@@ -22,6 +22,7 @@ const {
   decrementPendingRequest,
   checkAndIncrementPendingRequest,
   isSteerPreemptSupported,
+  isStopConfirmed,
   toPendingSteer,
 } = require('@librechat/api');
 const { disposeClient } = require('~/server/cleanup');
@@ -608,7 +609,12 @@ const ResumeAgentController = async (req, res, next, initializeClient, addTitle)
         expectedCreatedAt: job.createdAt,
         awaitProviderDrain: true,
       });
-      stopped = abortResult != null && abortResult.failureReason == null;
+      // `success` is the authoritative signal, exactly as the abort route gates. A
+      // `success: false` result WITHOUT a failure reason no longer exists — an
+      // unreached job, a replacement, or a lost CAS all report one — so the old
+      // `failureReason == null` test settled the occurrence and pruned the
+      // checkpoint on aborts that were never confirmed.
+      stopped = isStopConfirmed(abortResult);
     } catch (error) {
       logger.warn('[ResumeAgentController] Failed to stop inactive scheduled run', error);
     }
@@ -979,7 +985,9 @@ const ResumeAgentController = async (req, res, next, initializeClient, addTitle)
           expectedCreatedAt: job.createdAt,
           awaitProviderDrain: true,
         });
-        stopped = abortResult != null && abortResult.failureReason == null;
+        // Same authoritative gate as the inactive-schedule path above: only a landed
+        // abort (or an already-terminal, drained generation) may settle this occurrence.
+        stopped = isStopConfirmed(abortResult);
       } catch (error) {
         logger.warn('[ResumeAgentController] Failed to stop stale scheduled resume', error);
       }
diff --git a/api/server/index.js b/api/server/index.js
index 9203250d70..539836cef6 100644
--- a/api/server/index.js
+++ b/api/server/index.js
@@ -43,6 +43,7 @@ const {
   updateInterfacePermissions,
   configureMessageFilterRegexValidator,
   configureFileConfigRegexEngine,
+  createScheduleWriteGate,
   waitForKeyvRedisClient,
 } = require('@librechat/api');
 const { connectDb, indexSync } = require('~/db');
@@ -86,12 +87,11 @@ const trusted_proxy = Number(TRUST_PROXY) || 1; /* trust first proxy by default
 
 const app = express();
 let serverReady = false;
-let schedulesReady = false;
+/** @type {import('@librechat/api').ScheduleEngineState} */
+let scheduleEngineState = 'starting';
 
 const SERVER_NOT_READY_CODE = 'SERVER_NOT_READY';
 const CHAT_START_RETRY_AFTER_SECONDS = '1';
-const SCHEDULES_NOT_READY_CODE = 'SCHEDULES_NOT_READY';
-const SCHEDULE_ENGINE_OPTIONAL_METHODS = new Set(['GET', 'HEAD', 'OPTIONS', 'DELETE']);
 
 const rejectChatStartsUntilReady = (req, res, next) => {
   if (serverReady || req.method !== 'POST' || req.path === '/abort') {
@@ -105,16 +105,10 @@ const rejectChatStartsUntilReady = (req, res, next) => {
   });
 };
 
-const rejectScheduleWritesUntilReady = (req, res, next) => {
-  if (schedulesReady || SCHEDULE_ENGINE_OPTIONAL_METHODS.has(req.method)) {
-    return next();
-  }
-  res.set('Retry-After', CHAT_START_RETRY_AFTER_SECONDS);
-  return res.status(503).json({
-    code: SCHEDULES_NOT_READY_CODE,
-    error: 'Scheduler is still starting. Please retry shortly.',
-  });
-};
+const rejectScheduleWritesUntilReady = createScheduleWriteGate({
+  getState: () => scheduleEngineState,
+  retryAfterSeconds: CHAT_START_RETRY_AFTER_SECONDS,
+});
 
 const configureGenerationStreams = () => {
   const streamServices = createStreamServices();
@@ -419,9 +413,16 @@ const startServer = async () => {
         memoryDiagnostics.start();
       }
       await initializeAgentTriggerService({ address: server.address() });
-      schedulesReady = (await initializeScheduleEngine()) != null;
-      if (!schedulesReady) {
-        logger.warn('[schedules] write routes remain unavailable because the engine did not arm.');
+      const scheduleEngineArmed = (await initializeScheduleEngine()) != null;
+      scheduleEngineState = scheduleEngineArmed ? 'armed' : 'unavailable';
+      if (!scheduleEngineArmed) {
+        // Terminal, not transient: arming is attempted once, so schedule writes are refused
+        // for the life of this process. Logged at error level because the only other signal
+        // an operator gets is a 503 on every write — every other health signal stays green.
+        logger.error(
+          '[schedules] write routes are PERMANENTLY unavailable in this process: the engine did not arm. ' +
+            'Resolve the cause logged above and restart.',
+        );
       }
       serverReady = true;
       logger.info('Server readiness checks passing.');
diff --git a/packages/api/src/schedules/index.ts b/packages/api/src/schedules/index.ts
index 4abce8246d..bc2755a66a 100644
--- a/packages/api/src/schedules/index.ts
+++ b/packages/api/src/schedules/index.ts
@@ -4,5 +4,6 @@ export * from './engine';
 export * from './erasure';
 export * from './fire';
 export * from './handlers';
+export * from './readiness';
 export * from './trigger';
 export * from './types';
diff --git a/packages/api/src/schedules/readiness.spec.ts b/packages/api/src/schedules/readiness.spec.ts
new file mode 100644
index 0000000000..9e3f358210
--- /dev/null
+++ b/packages/api/src/schedules/readiness.spec.ts
@@ -0,0 +1,92 @@
+import type { Response } from 'express';
+import type { ScheduleEngineState } from './readiness';
+import {
+  createScheduleWriteGate,
+  SCHEDULES_NOT_READY_CODE,
+  SCHEDULES_UNAVAILABLE_CODE,
+} from './readiness';
+
+function makeRes() {
+  const res = {
+    statusCode: 0,
+    body: undefined as unknown,
+    headers: {} as Record<string, string>,
+    set(name: string, value: string) {
+      res.headers[name] = value;
+      return res;
+    },
+    status(code: number) {
+      res.statusCode = code;
+      return res;
+    },
+    json(payload: unknown) {
+      res.body = payload;
+      return res;
+    },
+  };
+  return res;
+}
+
+function run(state: ScheduleEngineState, method: string) {
+  const res = makeRes();
+  const next = jest.fn();
+  createScheduleWriteGate({ getState: () => state, retryAfterSeconds: '1' })(
+    { method },
+    res as unknown as Response,
+    next,
+  );
+  return { res, next };
+}
+
+describe('createScheduleWriteGate', () => {
+  it('passes writes through once the engine is armed', () => {
+    const { res, next } = run('armed', 'POST');
+    expect(next).toHaveBeenCalled();
+    expect(res.statusCode).toBe(0);
+  });
+
+  it.each(['GET', 'HEAD', 'OPTIONS', 'DELETE'])(
+    'never blocks %s, which does not need the engine',
+    (method) => {
+      for (const state of ['starting', 'unavailable'] as ScheduleEngineState[]) {
+        const { res, next } = run(state, method);
+        expect(next).toHaveBeenCalled();
+        expect(res.statusCode).toBe(0);
+      }
+    },
+  );
+
+  it('advertises a retry only while arming is genuinely still pending', () => {
+    const { res, next } = run('starting', 'POST');
+    expect(next).not.toHaveBeenCalled();
+    expect(res.statusCode).toBe(503);
+    expect(res.headers['Retry-After']).toBe('1');
+    expect(res.body).toMatchObject({ code: SCHEDULES_NOT_READY_CODE });
+  });
+
+  it('refuses terminally, without Retry-After, once arming has failed', () => {
+    const { res, next } = run('unavailable', 'POST');
+    expect(next).not.toHaveBeenCalled();
+    expect(res.statusCode).toBe(503);
+    // Nothing re-attempts arming, so a client obeying Retry-After here would poll a
+    // condition that cannot change without operator action.
+    expect(res.headers['Retry-After']).toBeUndefined();
+    expect(res.body).toMatchObject({ code: SCHEDULES_UNAVAILABLE_CODE });
+  });
+
+  it('re-reads the state on every request rather than capturing it at construction', () => {
+    let state: ScheduleEngineState = 'starting';
+    const gate = createScheduleWriteGate({ getState: () => state, retryAfterSeconds: '1' });
+
+    const blocked = makeRes();
+    gate({ method: 'POST' }, blocked as unknown as Response, jest.fn());
+    expect(blocked.statusCode).toBe(503);
+
+    state = 'armed';
+    const allowed = makeRes();
+    const next = jest.fn();
+    gate({ method: 'POST' }, allowed as unknown as Response, next);
+    expect(next).toHaveBeenCalled();
+    expect(allowed.statusCode).toBe(0);
+  });
+});
diff --git a/packages/api/src/schedules/readiness.ts b/packages/api/src/schedules/readiness.ts
new file mode 100644
index 0000000000..3f5cc36f94
--- /dev/null
+++ b/packages/api/src/schedules/readiness.ts
@@ -0,0 +1,66 @@
+import type { Response, NextFunction } from 'express';
+
+export const SCHEDULES_NOT_READY_CODE = 'SCHEDULES_NOT_READY';
+export const SCHEDULES_UNAVAILABLE_CODE = 'SCHEDULES_UNAVAILABLE';
+
+/**
+ * Whether the schedule engine has been armed for this process.
+ *
+ * `starting` and `unavailable` both refuse writes, but they are not the same condition:
+ * arming is attempted EXACTLY ONCE at boot, so a failed arm is terminal for the life of
+ * the process. Collapsing the two into a single flag is what let a permanent outage be
+ * advertised with `Retry-After`.
+ */
+export type ScheduleEngineState = 'starting' | 'armed' | 'unavailable';
+
+/**
+ * Reads and deletes never touch the engine: listing schedules, and removing one so it can
+ * no longer fire, must keep working even where nothing is armed.
+ */
+const ENGINE_OPTIONAL_METHODS = new Set(['GET', 'HEAD', 'OPTIONS', 'DELETE']);
+
+export interface ScheduleWriteGateOptions {
+  getState: () => ScheduleEngineState;
+  /** `Retry-After` for the genuinely transient window only. */
+  retryAfterSeconds: string;
+}
+
+export type ScheduleWriteGate = (
+  req: { method: string },
+  res: Response,
+  next: NextFunction,
+) => Response | void;
+
+/**
+ * Guards schedule writes on engine readiness, answering with the retry contract that
+ * matches the real state: retry while arming is still pending, and a terminal refusal once
+ * it has definitively failed — nothing re-attempts arming, so a client obeying
+ * `Retry-After` there would poll a condition that cannot change without operator action.
+ */
+export function createScheduleWriteGate({
+  getState,
+  retryAfterSeconds,
+}: ScheduleWriteGateOptions): ScheduleWriteGate {
+  return function rejectScheduleWritesUntilReady(
+    req: { method: string },
+    res: Response,
+    next: NextFunction,
+  ): Response | void {
+    const state = getState();
+    if (state === 'armed' || ENGINE_OPTIONAL_METHODS.has(req.method)) {
+      return next();
+    }
+    if (state === 'starting') {
+      res.set('Retry-After', retryAfterSeconds);
+      return res.status(503).json({
+        code: SCHEDULES_NOT_READY_CODE,
+        error: 'Scheduler is still starting. Please retry shortly.',
+      });
+    }
+    return res.status(503).json({
+      code: SCHEDULES_UNAVAILABLE_CODE,
+      error:
+        'Scheduler is unavailable in this deployment. Retrying will not help — check the server logs and resolve the startup failure.',
+    });
+  };
+}
diff --git a/packages/api/src/schedules/service.spec.ts b/packages/api/src/schedules/service.spec.ts
index efc00f97b7..1c609baad0 100644
--- a/packages/api/src/schedules/service.spec.ts
+++ b/packages/api/src/schedules/service.spec.ts
@@ -1584,7 +1584,7 @@ describe('provider-drained schedule aborts', () => {
       })),
     } as unknown as typeof mockJobStore;
     const manager = jest.requireMock('../stream/GenerationJobManager').GenerationJobManager;
-    manager.abortJob = jest.fn(async () => ({ success: false }));
+    manager.abortJob = jest.fn(async () => ({ success: false, failureReason: 'already_settled' }));
 
     const delivered = await service.engineDeps.abortScheduledJob(
       'c1',
@@ -1598,6 +1598,35 @@ describe('provider-drained schedule aborts', () => {
     expect(delivered).toBe(true);
   });
 
+  it.each(['generation_replaced', 'job_still_active', 'job_not_found'] as const)(
+    'reports %s as an undelivered abort',
+    async (failureReason) => {
+      const service = makeService(jest.fn<Promise<ActiveRun[]>, [string]>().mockResolvedValue([]));
+      const deleteJob = jest.fn(async () => true);
+      mockJobStore = {
+        getJob: jest.fn(async () => ({
+          status: 'running',
+          createdAt: 7,
+          scheduleId: 's1',
+          scheduledFor: '2026-01-01T00:00:00.000Z',
+        })),
+        deleteJob,
+      } as unknown as typeof mockJobStore;
+      const manager = jest.requireMock('../stream/GenerationJobManager').GenerationJobManager;
+      manager.abortJob = jest.fn(async () => ({ success: false, failureReason }));
+
+      const delivered = await service.engineDeps.abortScheduledJob(
+        'c1',
+        { scheduleId: 's1', scheduledFor: '2026-01-01T00:00:00.000Z' },
+        { preserve: false },
+      );
+
+      expect(delivered).toBe(false);
+      // Never destroy evidence for a generation this call did not stop.
+      expect(deleteJob).not.toHaveBeenCalled();
+    },
+  );
+
   it('deletes terminal evidence only after the exact provider drain is confirmed', async () => {
     const service = makeService(jest.fn<Promise<ActiveRun[]>, [string]>().mockResolvedValue([]));
     const deleteJob = jest.fn(async () => true);
@@ -1611,7 +1640,7 @@ describe('provider-drained schedule aborts', () => {
       deleteJob,
     } as unknown as typeof mockJobStore;
     const manager = jest.requireMock('../stream/GenerationJobManager').GenerationJobManager;
-    manager.abortJob = jest.fn(async () => ({ success: false }));
+    manager.abortJob = jest.fn(async () => ({ success: false, failureReason: 'already_settled' }));
 
     const delivered = await service.engineDeps.abortScheduledJob(
       'c1',
diff --git a/packages/api/src/schedules/service.ts b/packages/api/src/schedules/service.ts
index 393a724228..6aa16fd256 100644
--- a/packages/api/src/schedules/service.ts
+++ b/packages/api/src/schedules/service.ts
@@ -24,6 +24,7 @@ import {
 import { deleteAgentCheckpoint, captureAgentCheckpointGeneration } from '../agents/checkpointer';
 import { fireSchedule, BALANCE_SKIP_DISABLE_THRESHOLD } from './fire';
 import { GenerationJobManager } from '../stream/GenerationJobManager';
+import { isStopConfirmed } from '../stream/interfaces/IJobStore';
 import { buildBalanceUpdateFields } from '../middleware/balance';
 import { getAppConfigOptionsFromUser } from '../app/service';
 import { isShutdownInProgress } from '../app/shutdown';
@@ -568,10 +569,9 @@ export function createSchedulesService(
         expectedCreatedAt: job.createdAt,
         awaitProviderDrain: true,
       });
-      if (
-        aborted.failureReason === 'generation_replaced' ||
-        aborted.failureReason === 'job_still_active'
-      ) {
+      // Terminal-and-drained counts as delivered (see above); a replacement, a still-live
+      // run, or a job that vanished before the transition does not.
+      if (!isStopConfirmed(aborted)) {
         return false;
       }
       if (options?.preserve === false) {
diff --git a/packages/api/src/stream/GenerationJobManager.ts b/packages/api/src/stream/GenerationJobManager.ts
index 4b40b6c205..3a89dfb2d9 100644
--- a/packages/api/src/stream/GenerationJobManager.ts
+++ b/packages/api/src/stream/GenerationJobManager.ts
@@ -270,6 +270,28 @@ function isRecoverableTakeoverSplit(
   );
 }
 
+/**
+ * Name the reason a terminal-state CAS was lost, off the job that now holds the
+ * conversation. Losing to natural completion IS a stop; losing to a replacement, or to
+ * deletion, is not — and callers settle durable state on that distinction.
+ */
+function classifyLostAbortRace(
+  jobStillActive: boolean,
+  currentJob: SerializableJobData | null,
+  abortedCreatedAt: number,
+): NonNullable<AbortResult['failureReason']> {
+  if (jobStillActive) {
+    return 'job_still_active';
+  }
+  if (currentJob == null) {
+    return 'job_not_found';
+  }
+  if (currentJob.createdAt !== abortedCreatedAt) {
+    return 'generation_replaced';
+  }
+  return 'already_settled';
+}
+
 function buildTerminalPersistenceReconcile(
   job: Pick<SerializableJobData, 'createdAt' | 'conversationId' | 'status'>,
 ): t.FinalEvent {
@@ -3709,6 +3731,10 @@ class GenerationJobManagerClass {
         content: [],
         jobData: null,
         success: false,
+        /** The job vanished between the caller's read and this one. No transition
+         * was made and no provider drain was awaited, so this says nothing about
+         * whether trailing owner work is still in flight. */
+        failureReason: 'job_not_found',
         finalEvent: null,
         collectedUsage: [],
       };
@@ -3726,6 +3752,10 @@ class GenerationJobManagerClass {
           content: [],
           jobData: unlockedJob,
           success: false,
+          /** The pause never unlocked for THIS generation: the job was either deleted
+           * outright or a replacement took the conversation. A replacement is another
+           * run's state — settling or pruning on it would destroy the successor. */
+          failureReason: unlockedJob == null ? 'job_not_found' : 'generation_replaced',
           finalEvent: null,
           collectedUsage: [],
         };
@@ -3748,6 +3778,10 @@ class GenerationJobManagerClass {
         content: [],
         jobData,
         success: false,
+        /** No transition was needed: the generation is already terminal, and the
+         * drain above (when requested) proves its provider segment can no longer
+         * persist. This is a stop, just not one this call made. */
+        failureReason: 'already_settled',
         finalEvent: null,
         collectedUsage: [],
       };
@@ -3845,13 +3879,9 @@ class GenerationJobManagerClass {
       }
       return {
         success: false,
-        ...(jobStillActive
-          ? { failureReason: 'job_still_active' as const }
-          : options?.expectedCreatedAt != null &&
-            currentJob != null &&
-            currentJob?.createdAt !== options.expectedCreatedAt && {
-              failureReason: 'generation_replaced' as const,
-            }),
+        /** The drain above already ran when the caller required one, so an
+         * `already_settled` verdict here is a fully drained generation. */
+        failureReason: classifyLostAbortRace(jobStillActive, currentJob, jobData.createdAt),
         jobData,
         content: abortContent,
         finalEvent: null,
diff --git a/packages/api/src/stream/__tests__/abortFailureReason.spec.ts b/packages/api/src/stream/__tests__/abortFailureReason.spec.ts
new file mode 100644
index 0000000000..2a283cf1b5
--- /dev/null
+++ b/packages/api/src/stream/__tests__/abortFailureReason.spec.ts
@@ -0,0 +1,132 @@
+/**
+ * Every `success: false` abort must name WHY it failed. Callers that settle durable
+ * state on an abort (schedule outcomes, checkpoint pruning) previously inferred a
+ * confirmed stop from the ABSENCE of a failure reason, which silently swept in the
+ * unlabeled not-found and already-terminal paths.
+ */
+import type { AbortResult } from '../interfaces/IJobStore';
+import { isStopConfirmed } from '../interfaces/IJobStore';
+
+/** Suppress winston Console transport output (survives jest.resetModules) */
+jest.spyOn(console, 'log').mockImplementation();
+
+async function configureManager() {
+  const { GenerationJobManager } = await import('../GenerationJobManager');
+  const { InMemoryJobStore } = await import('../implementations/InMemoryJobStore');
+  const { InMemoryEventTransport } = await import('../implementations/InMemoryEventTransport');
+
+  GenerationJobManager.configure({
+    jobStore: new InMemoryJobStore(),
+    eventTransport: new InMemoryEventTransport(),
+    isRedis: false,
+    cleanupOnComplete: false,
+  });
+  GenerationJobManager.initialize();
+  return GenerationJobManager;
+}
+
+describe('abortJob failure reasons', () => {
+  beforeEach(() => {
+    jest.resetModules();
+  });
+
+  it('reports job_not_found when nothing occupies the stream', async () => {
+    const manager = await configureManager();
+
+    const result = await manager.abortJob('never-created');
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toBe('job_not_found');
+    expect(isStopConfirmed(result)).toBe(false);
+
+    await manager.destroy();
+  });
+
+  it('reports already_settled for a generation that is terminal before the call', async () => {
+    const manager = await configureManager();
+    const streamId = 'abort-twice';
+    await manager.createJob(streamId, 'user-1');
+
+    const first = await manager.abortJob(streamId);
+    expect(first.success).toBe(true);
+
+    const second = await manager.abortJob(streamId);
+
+    expect(second.success).toBe(false);
+    expect(second.failureReason).toBe('already_settled');
+    // No transition was needed — the generation is already stopped, so a caller may
+    // still settle on it. This is the ONE failure reason that confirms a stop.
+    expect(isStopConfirmed(second)).toBe(true);
+
+    await manager.destroy();
+  });
+
+  it('reports generation_replaced when the epoch fence rejects a stale abort', async () => {
+    const manager = await configureManager();
+    const streamId = 'epoch-fenced';
+    const job = await manager.createJob(streamId, 'user-1');
+
+    const result = await manager.abortJob(streamId, {
+      expectedCreatedAt: job.createdAt - 1,
+    });
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toBe('generation_replaced');
+    expect(isStopConfirmed(result)).toBe(false);
+
+    await manager.destroy();
+  });
+
+  it('leaves no unlabeled failure across the reachable abort outcomes', async () => {
+    const manager = await configureManager();
+    const streamId = 'labeled';
+    const job = await manager.createJob(streamId, 'user-1');
+
+    const results = [
+      await manager.abortJob('missing'),
+      await manager.abortJob(streamId, { expectedCreatedAt: job.createdAt - 1 }),
+      await manager.abortJob(streamId),
+      await manager.abortJob(streamId),
+    ];
+
+    for (const result of results) {
+      expect(result.success === true || result.failureReason != null).toBe(true);
+    }
+
+    await manager.destroy();
+  });
+});
+
+describe('isStopConfirmed', () => {
+  const base: AbortResult = {
+    success: false,
+    jobData: null,
+    content: [],
+    finalEvent: null,
+    text: '',
+    collectedUsage: [],
+  };
+
+  it('confirms a landed abort', () => {
+    expect(isStopConfirmed({ ...base, success: true })).toBe(true);
+  });
+
+  it('confirms an already-terminal generation', () => {
+    expect(isStopConfirmed({ ...base, failureReason: 'already_settled' })).toBe(true);
+  });
+
+  it.each(['generation_replaced', 'job_still_active', 'job_not_found'] as const)(
+    'refuses to confirm %s',
+    (failureReason) => {
+      expect(isStopConfirmed({ ...base, failureReason })).toBe(false);
+    },
+  );
+
+  it('refuses to confirm a bare failure with no reason', () => {
+    expect(isStopConfirmed(base)).toBe(false);
+  });
+
+  it.each([null, undefined])('refuses to confirm %p', (result) => {
+    expect(isStopConfirmed(result)).toBe(false);
+  });
+});
diff --git a/packages/api/src/stream/__tests__/startup.spec.ts b/packages/api/src/stream/__tests__/startup.spec.ts
index 7c7b3da8d0..7298dd4026 100644
--- a/packages/api/src/stream/__tests__/startup.spec.ts
+++ b/packages/api/src/stream/__tests__/startup.spec.ts
@@ -2278,7 +2278,9 @@ describe('GenerationJobManager startup telemetry', () => {
 
       const result = await aborting;
       expect(result).toMatchObject({ success: false, finalEvent: null });
-      expect(result.failureReason).toBeUndefined();
+      // Deletion is named for what it is. The point of this test is that it is NOT
+      // reported as a replacement — nothing took the conversation over.
+      expect(result.failureReason).toBe('job_not_found');
       expect(job.abortController.signal.aborted).toBe(true);
     } finally {
       releaseTransition?.();
diff --git a/packages/api/src/stream/index.ts b/packages/api/src/stream/index.ts
index 05995fd142..6ef140e0ae 100644
--- a/packages/api/src/stream/index.ts
+++ b/packages/api/src/stream/index.ts
@@ -28,6 +28,9 @@ export {
   isPendingActionExpired,
   isPendingActionStale,
 } from './interfaces/IJobStore';
+// Canonical "did this generation actually stop?" predicate — shared by every caller
+// that settles durable state on an abort's outcome.
+export { isStopConfirmed } from './interfaces/IJobStore';
 export {
   STEER_ENQUEUE_NOT_RUNNING,
   STEER_ENQUEUE_QUEUE_FULL,
diff --git a/packages/api/src/stream/interfaces/IJobStore.ts b/packages/api/src/stream/interfaces/IJobStore.ts
index 50cb847ebc..a03e28298d 100644
--- a/packages/api/src/stream/interfaces/IJobStore.ts
+++ b/packages/api/src/stream/interfaces/IJobStore.ts
@@ -608,10 +608,13 @@ export interface UsageMetadata {
 export interface AbortResult {
   /** Whether the abort was successful */
   success: boolean;
-  /** Distinguishes an epoch-fenced abort from ordinary not-found/terminal
-   * failures so an HTTP caller can return RUN_REPLACED instead of silently
-   * reporting success for a newer generation it deliberately did not stop. */
-  failureReason?: 'generation_replaced' | 'job_still_active';
+  /** Why the abort did not land. EVERY `success: false` return carries one, so a
+   * caller can separate a generation it must not settle (`generation_replaced`,
+   * `job_not_found`) from one that is still live (`job_still_active`) and from one
+   * that had already reached a terminal state (`already_settled` — the provider has
+   * also drained when `awaitProviderDrain` was requested). The ABSENCE of this field
+   * is not a stop confirmation; use `isStopConfirmed`. */
+  failureReason?: 'generation_replaced' | 'job_still_active' | 'job_not_found' | 'already_settled';
   /** The generation was stopped, but the caller's required durable side
    * effects failed before normal FINAL publication. The manager emitted a
    * conservative reconciliation frame instead. */
@@ -630,6 +633,22 @@ export interface AbortResult {
   pendingSteers?: TPendingSteer[];
 }
 
+/**
+ * Canonical "did this generation actually stop?" predicate — one definition shared by
+ * every caller that settles durable state on the answer (schedule outcomes, checkpoint
+ * pruning, capacity release).
+ *
+ * A landed abort confirms the stop. So does `already_settled`: the generation reached a
+ * terminal state on its own and, when the caller asked for `awaitProviderDrain`, its
+ * provider segment has drained, so nothing can still write. Every OTHER failure leaves a
+ * generation that is either still live (`job_still_active`), owned by someone else
+ * (`generation_replaced`), or unobservable from here without a drain (`job_not_found`) —
+ * none of which may be settled on.
+ */
+export function isStopConfirmed(result: AbortResult | null | undefined): boolean {
+  return result != null && (result.success === true || result.failureReason === 'already_settled');
+}
+
 /**
  * Resume state for reconnecting clients
  */