diff --git a/api/server/routes/agents/__tests__/idempotencyLimiter.spec.js b/api/server/routes/agents/__tests__/idempotencyLimiter.spec.js
new file mode 100644
index 0000000000..e7281ee2ed
--- /dev/null
+++ b/api/server/routes/agents/__tests__/idempotencyLimiter.spec.js
@@ -0,0 +1,153 @@
+const express = require('express');
+const request = require('supertest');
+
+const mockHasGenerationClaim = jest.fn();
+const mockIpLimiter = jest.fn((_req, res) => res.status(429).json({ limited: 'ip' }));
+const mockUserLimiter = jest.fn((_req, res) => res.status(429).json({ limited: 'user' }));
+const mockRetryLimiter = jest.fn((_req, _res, next) => next());
+const mockRetryProbeLimiter = jest.fn((_req, _res, next) => next());
+const mockExemptAgentTrigger = jest.fn(() => false);
+const mockExemptSchedule = jest.fn(() => false);
+
+jest.mock('@librechat/data-schemas', () => ({
+  logger: {
+    debug: jest.fn(),
+    warn: jest.fn(),
+    error: jest.fn(),
+    info: jest.fn(),
+  },
+}));
+
+jest.mock('@librechat/api', () => ({
+  isEnabled: jest.fn(() => true),
+  detectGenerationRetry: async (req, _res, next) => {
+    req._isConfirmedGenerationRetry = await mockHasGenerationClaim(
+      req.user?.id,
+      req.body?.clientRequestId,
+    );
+    next();
+  },
+  isConfirmedGenerationRetry: (req) => req._isConfirmedGenerationRetry === true,
+  generationRetryProbeLimiter: (...args) => mockRetryProbeLimiter(...args),
+  generationRetryLimiter: (...args) => mockRetryLimiter(...args),
+  isAgentTriggerRequest: jest.fn(() => false),
+  captureScheduleFireContext: jest.fn(),
+  exemptAgentTriggerFromIpLimiter: (...args) => mockExemptAgentTrigger(...args),
+  exemptFromUserLimiter: (...args) => mockExemptSchedule(...args),
+  createMessageFilterPii: jest.fn(() => (_req, _res, next) => next()),
+}));
+
+jest.mock('~/server/middleware', () => ({
+  uaParser: (_req, _res, next) => next(),
+  checkBan: (_req, _res, next) => next(),
+  requireJwtAuth: (req, _res, next) => {
+    req.user = { id: 'user-1' };
+    next();
+  },
+  moderateText: (_req, _res, next) => next(),
+  messageIpLimiter: (...args) => mockIpLimiter(...args),
+  configMiddleware: (_req, _res, next) => next(),
+  messageUserLimiter: (...args) => mockUserLimiter(...args),
+}));
+
+jest.mock('~/server/routes/agents/chat', () => {
+  const router = require('express').Router();
+  router.post('/', (_req, res) => res.status(201).json({ admitted: true }));
+  return router;
+});
+jest.mock('~/server/routes/agents/v1', () => ({
+  v1: require('express').Router(),
+}));
+jest.mock('~/server/routes/agents/openai', () => require('express').Router());
+jest.mock('~/server/routes/agents/responses', () => require('express').Router());
+jest.mock('~/server/controllers/agents/steer', () => {
+  const controller = (_req, _res, next) => next();
+  controller.SteerDeliveryController = (_req, _res, next) => next();
+  controller.SteerCancelController = (_req, _res, next) => next();
+  controller.SteerArmController = (_req, _res, next) => next();
+  return controller;
+});
+jest.mock('~/models', () => ({}));
+jest.mock('~/server/services/Schedules', () => ({}));
+
+const agentsRouter = require('../index');
+const app = express();
+app.use(express.json());
+app.use('/agents', agentsRouter);
+
+describe('start-generation idempotency before message limiters', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    mockExemptAgentTrigger.mockReturnValue(false);
+    mockExemptSchedule.mockReturnValue(false);
+  });
+
+  it('lets a confirmed retry reach the controller without consuming either limiter', async () => {
+    mockHasGenerationClaim.mockResolvedValue(true);
+
+    const response = await request(app).post('/agents/chat').send({ clientRequestId: 'request-1' });
+
+    expect(response.status).toBe(201);
+    expect(mockRetryProbeLimiter).toHaveBeenCalledTimes(1);
+    expect(mockRetryLimiter).toHaveBeenCalledTimes(1);
+    expect(mockIpLimiter).not.toHaveBeenCalled();
+    expect(mockUserLimiter).not.toHaveBeenCalled();
+  });
+
+  it('keeps a new submission behind the configured message limiters', async () => {
+    mockHasGenerationClaim.mockResolvedValue(false);
+
+    const response = await request(app).post('/agents/chat').send({ clientRequestId: 'request-2' });
+
+    expect(response.status).toBe(429);
+    expect(response.body).toEqual({ limited: 'ip' });
+    expect(mockRetryProbeLimiter).toHaveBeenCalledTimes(1);
+    expect(mockRetryLimiter).toHaveBeenCalledTimes(1);
+    expect(mockIpLimiter).toHaveBeenCalledTimes(1);
+    expect(mockUserLimiter).not.toHaveBeenCalled();
+  });
+
+  it('defers an excessive confirmed retry before the chat pipeline', async () => {
+    mockHasGenerationClaim.mockResolvedValue(true);
+    mockRetryLimiter.mockImplementationOnce((_req, res) =>
+      res.status(503).json({ code: 'SERVER_NOT_READY' }),
+    );
+
+    const response = await request(app).post('/agents/chat').send({ clientRequestId: 'request-3' });
+
+    expect(response.status).toBe(503);
+    expect(response.body.code).toBe('SERVER_NOT_READY');
+    expect(mockIpLimiter).not.toHaveBeenCalled();
+    expect(mockUserLimiter).not.toHaveBeenCalled();
+  });
+
+  it('bounds candidate probes before durable storage inspection', async () => {
+    mockRetryProbeLimiter.mockImplementationOnce((_req, res) =>
+      res.status(503).json({ code: 'SERVER_NOT_READY' }),
+    );
+
+    const response = await request(app).post('/agents/chat').send({ clientRequestId: 'request-5' });
+
+    expect(response.status).toBe(503);
+    expect(mockHasGenerationClaim).not.toHaveBeenCalled();
+    expect(mockRetryLimiter).not.toHaveBeenCalled();
+    expect(mockIpLimiter).not.toHaveBeenCalled();
+    expect(mockUserLimiter).not.toHaveBeenCalled();
+  });
+
+  it.each([
+    ['an agent-trigger delivery', mockExemptAgentTrigger],
+    ['a scheduled delivery', mockExemptSchedule],
+  ])('keeps %s outside the human retry bucket', async (_label, exemption) => {
+    mockHasGenerationClaim.mockResolvedValue(true);
+    exemption.mockReturnValue(true);
+
+    const response = await request(app).post('/agents/chat').send({ clientRequestId: 'request-4' });
+
+    expect(response.status).toBe(201);
+    expect(mockRetryProbeLimiter).not.toHaveBeenCalled();
+    expect(mockRetryLimiter).not.toHaveBeenCalled();
+    expect(mockIpLimiter).not.toHaveBeenCalled();
+    expect(mockUserLimiter).not.toHaveBeenCalled();
+  });
+});
diff --git a/api/server/routes/agents/index.js b/api/server/routes/agents/index.js
index 460d960adc..b6c237708a 100644
--- a/api/server/routes/agents/index.js
+++ b/api/server/routes/agents/index.js
@@ -18,6 +18,10 @@ const {
   exemptAgentTriggerFromIpLimiter,
   captureScheduleFireContext,
   exemptFromUserLimiter: exemptScheduleFromUserLimiter,
+  detectGenerationRetry,
+  isConfirmedGenerationRetry,
+  generationRetryProbeLimiter,
+  generationRetryLimiter,
 } = require('@librechat/api');
 const { createSseStreamTelemetry } = require('@librechat/api/telemetry');
 const { logger } = require('@librechat/data-schemas');
@@ -1075,14 +1079,41 @@ router.post(
 router.use('/', v1);
 
 const chatRouter = express.Router();
+const useMessageIpLimiter = isEnabled(LIMIT_MESSAGE_IP);
+const useMessageUserLimiter = isEnabled(LIMIT_MESSAGE_USER);
 chatRouter.use(configMiddleware);
-
-if (isEnabled(LIMIT_MESSAGE_IP)) {
-  chatRouter.use(unless(exemptAgentTriggerFromIpLimiter, messageIpLimiter));
+if (useMessageIpLimiter || useMessageUserLimiter) {
+  chatRouter.use(
+    unless(
+      (req) => exemptAgentTriggerFromIpLimiter(req) || exemptScheduleFromUserLimiter(req),
+      generationRetryProbeLimiter,
+    ),
+  );
+  chatRouter.use(detectGenerationRetry);
+  chatRouter.use(
+    unless(
+      (req) => exemptAgentTriggerFromIpLimiter(req) || exemptScheduleFromUserLimiter(req),
+      generationRetryLimiter,
+    ),
+  );
 }
 
-if (isEnabled(LIMIT_MESSAGE_USER)) {
-  chatRouter.use(unless(exemptScheduleFromUserLimiter, messageUserLimiter));
+if (useMessageIpLimiter) {
+  chatRouter.use(
+    unless(
+      (req) => exemptAgentTriggerFromIpLimiter(req) || isConfirmedGenerationRetry(req),
+      messageIpLimiter,
+    ),
+  );
+}
+
+if (useMessageUserLimiter) {
+  chatRouter.use(
+    unless(
+      (req) => exemptScheduleFromUserLimiter(req) || isConfirmedGenerationRetry(req),
+      messageUserLimiter,
+    ),
+  );
 }
 
 chatRouter.use('/', chat);
diff --git a/package-lock.json b/package-lock.json
index e3d95633c0..bdddde990b 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -42783,6 +42783,7 @@
         "@langchain/langgraph-checkpoint-mongodb": "^1.4.0",
         "cluster-key-slot": "^1.1.2",
         "croner": "^10.0.1",
+        "express-rate-limit": "^8.5.1",
         "helmet": "^8.3.0",
         "proxy-from-env": "^2.1.0",
         "re2js": "^2.8.6"
diff --git a/packages/api/package.json b/packages/api/package.json
index 63d36cbc53..0a7a950209 100644
--- a/packages/api/package.json
+++ b/packages/api/package.json
@@ -171,6 +171,7 @@
     "@langchain/langgraph-checkpoint-mongodb": "^1.4.0",
     "cluster-key-slot": "^1.1.2",
     "croner": "^10.0.1",
+    "express-rate-limit": "^8.5.1",
     "helmet": "^8.3.0",
     "proxy-from-env": "^2.1.0",
     "re2js": "^2.8.6"
diff --git a/packages/api/src/middleware/generationRetry.spec.ts b/packages/api/src/middleware/generationRetry.spec.ts
new file mode 100644
index 0000000000..72970e5eaf
--- /dev/null
+++ b/packages/api/src/middleware/generationRetry.spec.ts
@@ -0,0 +1,144 @@
+import express from 'express';
+import request from 'supertest';
+import { logger } from '@librechat/data-schemas';
+import type { NextFunction, Request, Response } from 'express';
+import {
+  detectGenerationRetry,
+  generationRetryLimiter,
+  generationRetryProbeLimiter,
+  GENERATION_RETRY_MAX,
+  GENERATION_RETRY_PROBE_MAX,
+  isConfirmedGenerationRetry,
+} from './generationRetry';
+import { GenerationJobManager } from '~/stream/GenerationJobManager';
+
+function generationRequest(overrides: Partial<Request> = {}): Request {
+  return {
+    method: 'POST',
+    path: '/',
+    body: { clientRequestId: 'request-1' },
+    user: { id: 'user-1' },
+    ...overrides,
+  } as Request;
+}
+
+describe('generation retry admission', () => {
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  it('marks only a submission with an existing durable claim as a retry', async () => {
+    const hasClaim = jest.spyOn(GenerationJobManager, 'hasGenerationClaim').mockResolvedValue(true);
+    const req = generationRequest();
+    const next = jest.fn() as NextFunction;
+
+    await detectGenerationRetry(req, {} as Response, next);
+
+    expect(hasClaim).toHaveBeenCalledWith('user-1', 'request-1');
+    expect(isConfirmedGenerationRetry(req)).toBe(true);
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it('leaves a new submission subject to the ordinary message limiters', async () => {
+    jest.spyOn(GenerationJobManager, 'hasGenerationClaim').mockResolvedValue(false);
+    const req = generationRequest();
+
+    await detectGenerationRetry(req, {} as Response, jest.fn());
+
+    expect(isConfirmedGenerationRetry(req)).toBe(false);
+  });
+
+  it.each([
+    ['a resume', { path: '/resume' }],
+    ['a resume with a trailing slash', { path: '/resume/' }],
+    ['a case-insensitive resume route', { path: '/Resume' }],
+    ['a request without an authenticated user', { user: undefined }],
+    ['an invalid idempotency key', { body: { clientRequestId: 'invalid key' } }],
+  ])('does not probe %s', async (_label, overrides) => {
+    const hasClaim = jest.spyOn(GenerationJobManager, 'hasGenerationClaim');
+    const req = generationRequest(overrides as Partial<Request>);
+    const next = jest.fn() as NextFunction;
+
+    await detectGenerationRetry(req, {} as Response, next);
+
+    expect(hasClaim).not.toHaveBeenCalled();
+    expect(isConfirmedGenerationRetry(req)).toBe(false);
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it('fails closed to the ordinary limiters when the claim probe is unavailable', async () => {
+    jest
+      .spyOn(GenerationJobManager, 'hasGenerationClaim')
+      .mockRejectedValue(new Error('store unavailable'));
+    const warn = jest.spyOn(logger, 'warn').mockImplementation(() => logger);
+    const req = generationRequest();
+    const next = jest.fn() as NextFunction;
+
+    await detectGenerationRetry(req, {} as Response, next);
+
+    expect(isConfirmedGenerationRetry(req)).toBe(false);
+    expect(warn).toHaveBeenCalledWith(
+      '[GenerationIdempotency] Failed to inspect start-generation claim',
+      expect.objectContaining({ userId: 'user-1', clientRequestId: 'request-1' }),
+    );
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it('bounds fresh claim probes before accessing the shared store', async () => {
+    const hasClaim = jest
+      .spyOn(GenerationJobManager, 'hasGenerationClaim')
+      .mockResolvedValue(false);
+    const downstream = jest.fn((_req, res) => res.sendStatus(204));
+    const app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => {
+      req.user = { id: 'bounded-probe-user' };
+      next();
+    });
+    app.use(generationRetryProbeLimiter);
+    app.use(detectGenerationRetry);
+    app.post('/', downstream);
+
+    for (let attempt = 0; attempt < GENERATION_RETRY_PROBE_MAX; attempt += 1) {
+      await request(app)
+        .post('/')
+        .send({ clientRequestId: `probe-${attempt}` })
+        .expect(204);
+    }
+    const rejected = await request(app)
+      .post('/')
+      .send({ clientRequestId: 'probe-rejected' })
+      .expect(503);
+
+    expect(rejected.headers['retry-after']).toBeDefined();
+    expect(rejected.body.code).toBe('SERVER_NOT_READY');
+    expect(hasClaim).toHaveBeenCalledTimes(GENERATION_RETRY_PROBE_MAX);
+    expect(downstream).toHaveBeenCalledTimes(GENERATION_RETRY_PROBE_MAX);
+  });
+
+  it('makes a bounded confirmed retry delay participate in readiness recovery', async () => {
+    jest.spyOn(GenerationJobManager, 'hasGenerationClaim').mockResolvedValue(true);
+    const downstream = jest.fn((_req, res) => res.sendStatus(204));
+    const app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => {
+      req.user = { id: 'bounded-retry-user' };
+      next();
+    });
+    app.use(detectGenerationRetry);
+    app.use(generationRetryLimiter);
+    app.post('/', downstream);
+
+    for (let attempt = 0; attempt < GENERATION_RETRY_MAX; attempt += 1) {
+      await request(app).post('/').send({ clientRequestId: 'bounded-request' }).expect(204);
+    }
+    const rejected = await request(app)
+      .post('/')
+      .send({ clientRequestId: 'bounded-request' })
+      .expect(503);
+
+    expect(rejected.headers['retry-after']).toBeDefined();
+    expect(rejected.body.code).toBe('SERVER_NOT_READY');
+    expect(downstream).toHaveBeenCalledTimes(GENERATION_RETRY_MAX);
+  });
+});
diff --git a/packages/api/src/middleware/generationRetry.ts b/packages/api/src/middleware/generationRetry.ts
new file mode 100644
index 0000000000..b4e6416373
--- /dev/null
+++ b/packages/api/src/middleware/generationRetry.ts
@@ -0,0 +1,109 @@
+import { rateLimit } from 'express-rate-limit';
+import { logger } from '@librechat/data-schemas';
+import type { NextFunction, Request, RequestHandler, Response } from 'express';
+import { GenerationJobManager } from '~/stream/GenerationJobManager';
+import { limiterCache } from '~/cache/cacheFactory';
+
+const CLIENT_REQUEST_ID_PATTERN = /^[A-Za-z0-9:_-]{1,128}$/;
+const confirmedGenerationRetry: unique symbol = Symbol('confirmedGenerationRetry');
+
+export const GENERATION_RETRY_WINDOW_MS = 60_000;
+export const GENERATION_RETRY_MAX = 10;
+export const GENERATION_RETRY_PROBE_MAX = 60;
+
+type GenerationRetryRequest = Request & {
+  user?: { id?: string };
+  [confirmedGenerationRetry]?: boolean;
+};
+
+function isGenerationRetryCandidate(req: GenerationRetryRequest): boolean {
+  const clientRequestId = req.body?.clientRequestId;
+  const normalizedPath = req.path.replace(/\/+$/, '').toLowerCase();
+  return (
+    req.method === 'POST' &&
+    normalizedPath !== '/resume' &&
+    typeof req.user?.id === 'string' &&
+    typeof clientRequestId === 'string' &&
+    CLIENT_REQUEST_ID_PATTERN.test(clientRequestId)
+  );
+}
+
+/**
+ * Classifies only retries already represented by a durable generation claim.
+ * The controller still owns the authoritative claim/read transition.
+ */
+export async function detectGenerationRetry(
+  req: GenerationRetryRequest,
+  _res: Response,
+  next: NextFunction,
+): Promise<void> {
+  if (!isGenerationRetryCandidate(req)) {
+    next();
+    return;
+  }
+
+  const clientRequestId = req.body?.clientRequestId;
+  const userId = req.user?.id;
+  if (typeof userId !== 'string' || typeof clientRequestId !== 'string') {
+    next();
+    return;
+  }
+
+  try {
+    req[confirmedGenerationRetry] = await GenerationJobManager.hasGenerationClaim(
+      userId,
+      clientRequestId,
+    );
+  } catch (error) {
+    logger.warn('[GenerationIdempotency] Failed to inspect start-generation claim', {
+      userId,
+      clientRequestId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+  }
+  next();
+}
+
+export function isConfirmedGenerationRetry(req: Request): boolean {
+  return (req as GenerationRetryRequest)[confirmedGenerationRetry] === true;
+}
+
+const retryAdmissionHandler: RequestHandler = (_req, res) => {
+  res.status(503).type('application/json').json({
+    code: 'SERVER_NOT_READY',
+    error: 'Generation retry admission is temporarily busy. Please retry shortly.',
+  });
+};
+
+/**
+ * Bounds read-only claim probes before they touch the shared generation store.
+ * The retryable response participates in the client's existing 120-second
+ * readiness loop and express-rate-limit supplies its Retry-After header.
+ */
+export const generationRetryProbeLimiter: RequestHandler = rateLimit({
+  windowMs: GENERATION_RETRY_WINDOW_MS,
+  max: GENERATION_RETRY_PROBE_MAX,
+  standardHeaders: true,
+  legacyHeaders: false,
+  skip: (req) => !isGenerationRetryCandidate(req as GenerationRetryRequest),
+  keyGenerator: (req) => String((req as GenerationRetryRequest).user?.id),
+  store: limiterCache('generation_retry_probe_limiter'),
+  handler: retryAdmissionHandler,
+});
+
+/**
+ * Confirmed retries bypass the ordinary message buckets so a lost response can
+ * be recovered, but they still receive a small user-scoped allowance before
+ * moderation and the rest of the request pipeline. This bounds replay costs
+ * while leaving the authoritative generation claim unchanged.
+ */
+export const generationRetryLimiter: RequestHandler = rateLimit({
+  windowMs: GENERATION_RETRY_WINDOW_MS,
+  max: GENERATION_RETRY_MAX,
+  standardHeaders: true,
+  legacyHeaders: false,
+  skip: (req) => !isConfirmedGenerationRetry(req),
+  keyGenerator: (req) => String((req as GenerationRetryRequest).user?.id),
+  store: limiterCache('generation_retry_limiter'),
+  handler: retryAdmissionHandler,
+});
diff --git a/packages/api/src/middleware/index.ts b/packages/api/src/middleware/index.ts
index d6e06ea4dc..5b2ee6d8be 100644
--- a/packages/api/src/middleware/index.ts
+++ b/packages/api/src/middleware/index.ts
@@ -23,3 +23,4 @@ export * from './modelBoundContent';
 export * from './messageFilterPii';
 export * from './messageValidation';
 export * from './feedback';
+export * from './generationRetry';
diff --git a/packages/api/src/stream/GenerationJobManager.ts b/packages/api/src/stream/GenerationJobManager.ts
index 699300e92b..8669b5fb4c 100644
--- a/packages/api/src/stream/GenerationJobManager.ts
+++ b/packages/api/src/stream/GenerationJobManager.ts
@@ -2923,6 +2923,21 @@ class GenerationJobManagerClass {
     return { claimed: false, existing: primary, source: 'primary' };
   }
 
+  /** Checks the mixed-version admission key without creating or repairing a
+   * claim. This is deliberately weaker than `claimGeneration`: callers may
+   * use it only to exempt a confirmed retry from request rate limiting; the
+   * controller must still perform the authoritative claim transition. */
+  async hasGenerationClaim(userId: string, clientRequestId: string): Promise<boolean> {
+    if (!CLIENT_REQUEST_ID_PATTERN.test(clientRequestId)) {
+      return false;
+    }
+    return (
+      (await this.jobStore.hasIdempotencyKey?.(
+        this.legacyGenerationClaimKey(userId, clientRequestId),
+      )) === true
+    );
+  }
+
   private generationClaimKey(userId: string, clientRequestId: string, streamId: string): string {
     return `{${streamId}}:${userId}:${clientRequestId}`;
   }
diff --git a/packages/api/src/stream/__tests__/RedisJobStore.stream_integration.spec.ts b/packages/api/src/stream/__tests__/RedisJobStore.stream_integration.spec.ts
index db9162721d..3259a910cb 100644
--- a/packages/api/src/stream/__tests__/RedisJobStore.stream_integration.spec.ts
+++ b/packages/api/src/stream/__tests__/RedisJobStore.stream_integration.spec.ts
@@ -4229,6 +4229,26 @@ describe('RedisJobStore Integration Tests', () => {
       await store.destroy();
     });
 
+    test('probes claim existence without creating a missing key', async () => {
+      if (!ioredisClient) {
+        return;
+      }
+      const { RedisJobStore } = await import('../implementations/RedisJobStore');
+      const store = new RedisJobStore(ioredisClient);
+      await store.initialize();
+
+      const key = `user-1:req-probe-${Date.now()}`;
+      await expect(store.hasIdempotencyKey(key)).resolves.toBe(false);
+
+      await store.claimIdempotencyKey(key, { streamId: 's1', conversationId: 'c1' }, 1200);
+      await expect(store.hasIdempotencyKey(key)).resolves.toBe(true);
+
+      await store.releaseIdempotencyKey(key);
+      await expect(store.hasIdempotencyKey(key)).resolves.toBe(false);
+
+      await store.destroy();
+    });
+
     test('sets a bounded TTL on the claim', async () => {
       if (!ioredisClient) {
         return;
diff --git a/packages/api/src/stream/__tests__/idempotencyClaim.spec.ts b/packages/api/src/stream/__tests__/idempotencyClaim.spec.ts
index e9ed727c78..f1b0257451 100644
--- a/packages/api/src/stream/__tests__/idempotencyClaim.spec.ts
+++ b/packages/api/src/stream/__tests__/idempotencyClaim.spec.ts
@@ -51,6 +51,33 @@ describe('InMemoryJobStore.claimIdempotencyKey', () => {
     expect(second).toEqual({ claimed: false, existing: { streamId: 's1', conversationId: 'c1' } });
   });
 
+  it('probes an existing claim without creating a missing key', async () => {
+    await expect(store.hasIdempotencyKey('user:missing')).resolves.toBe(false);
+
+    await store.claimIdempotencyKey(
+      'user:existing',
+      { streamId: 's1', conversationId: 'c1' },
+      1200,
+    );
+
+    await expect(store.hasIdempotencyKey('user:existing')).resolves.toBe(true);
+    await expect(store.hasIdempotencyKey('user:missing')).resolves.toBe(false);
+  });
+
+  it('does not report an expired claim as existing', async () => {
+    jest.useFakeTimers();
+    try {
+      jest.setSystemTime(new Date('2026-08-29T00:00:00Z'));
+      await store.claimIdempotencyKey('user:expired', { streamId: 's1', conversationId: 'c1' }, 1);
+      await expect(store.hasIdempotencyKey('user:expired')).resolves.toBe(true);
+
+      jest.setSystemTime(new Date('2026-08-29T00:00:02Z'));
+      await expect(store.hasIdempotencyKey('user:expired')).resolves.toBe(false);
+    } finally {
+      jest.useRealTimers();
+    }
+  });
+
   it('lets a released key be claimed again', async () => {
     await store.claimIdempotencyKey('user:req', { streamId: 's1', conversationId: 'c1' }, 1200);
     await store.releaseIdempotencyKey('user:req');
@@ -197,6 +224,16 @@ describe('GenerationJobManager start-generation claim', () => {
     expect(typeof retry.existing?.claimedAt).toBe('number');
   });
 
+  it('detects only an already-claimed submission for pre-limiter retry admission', async () => {
+    await expect(manager.hasGenerationClaim('user-1', 'req-1')).resolves.toBe(false);
+
+    await manager.claimGeneration('user-1', 'req-1', 'stream-a', 'convo-a');
+
+    await expect(manager.hasGenerationClaim('user-1', 'req-1')).resolves.toBe(true);
+    await expect(manager.hasGenerationClaim('user-1', 'req-2')).resolves.toBe(false);
+    await expect(manager.hasGenerationClaim('user-2', 'req-1')).resolves.toBe(false);
+  });
+
   it('claims the exact legacy key before the same-slot primary with staggered TTLs', async () => {
     const claimSpy = jest.spyOn(store, 'claimIdempotencyKey');
     const result = await manager.claimGeneration(
diff --git a/packages/api/src/stream/implementations/InMemoryJobStore.ts b/packages/api/src/stream/implementations/InMemoryJobStore.ts
index f0ba55cfb7..888c708113 100644
--- a/packages/api/src/stream/implementations/InMemoryJobStore.ts
+++ b/packages/api/src/stream/implementations/InMemoryJobStore.ts
@@ -892,6 +892,18 @@ export class InMemoryJobStore implements IJobStoreV2 {
     return { claimed: true, existing: value };
   }
 
+  async hasIdempotencyKey(key: string): Promise<boolean> {
+    const existing = this.idempotencyClaims.get(key);
+    if (existing == null) {
+      return false;
+    }
+    if (existing.expiresAt > Date.now()) {
+      return true;
+    }
+    this.idempotencyClaims.delete(key);
+    return false;
+  }
+
   async takeoverIdempotencyKey(
     key: string,
     expected: IdempotencyClaimValue,
diff --git a/packages/api/src/stream/implementations/RedisJobStore.ts b/packages/api/src/stream/implementations/RedisJobStore.ts
index f339fe2e49..73a01b034b 100644
--- a/packages/api/src/stream/implementations/RedisJobStore.ts
+++ b/packages/api/src/stream/implementations/RedisJobStore.ts
@@ -2713,6 +2713,10 @@ export class RedisJobStore implements IJobStoreV2 {
     }
   }
 
+  async hasIdempotencyKey(key: string): Promise<boolean> {
+    return (await this.redis.exists(KEYS.idempotency(key))) === 1;
+  }
+
   async takeoverIdempotencyKey(
     key: string,
     expected: IdempotencyClaimValue,
diff --git a/packages/api/src/stream/interfaces/IJobStore.ts b/packages/api/src/stream/interfaces/IJobStore.ts
index e23238b483..a885ae6371 100644
--- a/packages/api/src/stream/interfaces/IJobStore.ts
+++ b/packages/api/src/stream/interfaces/IJobStore.ts
@@ -885,6 +885,11 @@ export interface IJobStore {
   ): Promise<IdempotencyClaimResult>;
   releaseIdempotencyKey(key: string): Promise<void>;
 
+  /** Read-only existence probe used to identify a confirmed retry before
+   * request-rate admission. Optional stores keep the conservative behavior
+   * where every request remains subject to the limiter. */
+  hasIdempotencyKey?(key: string): Promise<boolean>;
+
   deleteJob(streamId: string, expectedCreatedAt?: number): Promise<boolean>;
   hasJob(streamId: string): Promise<boolean>;
   getRunningJobs(): Promise<SerializableJobData[]>;