🔌 fix: Resolve MCP OAuth flow state race condition (#11941)

* 🔌 fix: Resolve MCP OAuth flow state race condition

The OAuth callback arrives before the flow state is stored because
`createFlow()` returns a long-running Promise that only resolves on
flow COMPLETION, not when the initial PENDING state is persisted.
Calling it fire-and-forget with `.catch(() => {})` meant the redirect
happened before the state existed, causing "Flow state not found"
errors.

Changes:
- Add `initFlow()` to FlowStateManager that stores PENDING state and
  returns immediately, decoupling state persistence from monitoring
- Await `initFlow()` before emitting the OAuth redirect so the
  callback always finds existing state
- Keep `createFlow()` in the background for monitoring, but log
  warnings instead of silently swallowing errors
- Increase FLOWS cache TTL from 3 minutes to 10 minutes to give
  users more time to complete OAuth consent screens

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* 🔌 refactor: Revert FLOWS cache TTL change

The race condition fix (initFlow) is sufficient on its own.
TTL configurability should be a separate enhancement via
librechat.yaml mcpSettings rather than a hardcoded increase.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* 🔌 fix: Address PR review — restore FLOWS TTL, fix blocking-path race, clean up dead args

- Restore FLOWS cache TTL to 10 minutes (was silently dropped back to 3)
- Add initFlow before oauthStart in blocking handleOAuthRequired path
  to guarantee state persistence before any redirect
- Pass {} to createFlow metadata arg (dead after initFlow writes state)
- Downgrade background monitor .catch from logger.warn to logger.debug
- Replace process.nextTick with Promise.resolve in test (correct semantics)
- Add initFlow TTL assertion test
- Add blocking-path ordering test (initFlow → oauthStart → createFlow)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/api/src/flow/manager.test.ts

@@ -24,7 +24,6 @@ class MockKeyv<T = string> {
     return this.store.get(key);
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
   async set(key: string, value: FlowState<T>, _ttl?: number): Promise<true> {
     this.store.set(key, value);
     return true;
@@ -160,6 +159,71 @@ describe('FlowStateManager', () => {
     }, 15000);
   });
 
+  describe('initFlow', () => {
+    const flowId = 'init-test-flow';
+    const type = 'test-type';
+    const flowKey = `${type}:${flowId}`;
+
+    it('stores a PENDING flow state in the cache', async () => {
+      await flowManager.initFlow(flowId, type, { serverName: 'test' });
+
+      const state = await store.get(flowKey);
+      expect(state).toBeDefined();
+      expect(state!.status).toBe('PENDING');
+      expect(state!.type).toBe(type);
+      expect(state!.metadata).toEqual({ serverName: 'test' });
+      expect(state!.createdAt).toBeGreaterThan(0);
+    });
+
+    it('overwrites an existing flow state', async () => {
+      await store.set(flowKey, {
+        type,
+        status: 'COMPLETED',
+        metadata: { old: true },
+        createdAt: Date.now() - 10000,
+      });
+
+      await flowManager.initFlow(flowId, type, { new: true });
+
+      const state = await store.get(flowKey);
+      expect(state!.status).toBe('PENDING');
+      expect(state!.metadata).toEqual({ new: true });
+    });
+
+    it('allows createFlow to find and monitor the pre-stored state', async () => {
+      // initFlow stores the PENDING state
+      await flowManager.initFlow(flowId, type, { preStored: true });
+
+      // createFlow should find the existing state and start monitoring
+      const flowPromise = flowManager.createFlow(flowId, type);
+
+      // Complete the flow so the monitor resolves
+      await new Promise((resolve) => setTimeout(resolve, 500));
+      await flowManager.completeFlow(flowId, type, 'success');
+
+      const result = await flowPromise;
+      expect(result).toBe('success');
+    }, 15000);
+
+    it('passes the configured TTL to keyv.set', async () => {
+      const setSpy = jest.spyOn(store, 'set');
+
+      await flowManager.initFlow(flowId, type, { serverName: 'test' });
+
+      expect(setSpy).toHaveBeenCalledWith(
+        flowKey,
+        expect.objectContaining({ status: 'PENDING' }),
+        30000,
+      );
+    });
+
+    it('propagates store write failures', async () => {
+      jest.spyOn(store, 'set').mockRejectedValueOnce(new Error('Store write failed'));
+
+      await expect(flowManager.initFlow(flowId, type)).rejects.toThrow('Store write failed');
+    });
+  });
+
   describe('deleteFlow', () => {
     const flowId = 'test-flow-123';
     const type = 'test-type';