Sync delay (#1707)

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## Description

Please provide a clear description of your changes.

---

## Type of Change

Please delete options that are not relevant.

- [ ] 🐛 Bug fix (non-breaking change which fixes an issue)
- [ ] ✨ New feature (non-breaking change which adds functionality)
- [ ] 💥 Breaking change (fix or feature with breaking changes)
- [ ] 📝 Documentation update
- [ ] 🎨 UI/UX improvement
- [ ] 🔒 Security enhancement
- [ ] ⚡ Performance improvement

## Areas Affected

Please check all that apply:

- [ ] Email Integration (Gmail, IMAP, etc.)
- [ ] User Interface/Experience
- [ ] Authentication/Authorization
- [ ] Data Storage/Management
- [ ] API Endpoints
- [ ] Documentation
- [ ] Testing Infrastructure
- [ ] Development Workflow
- [ ] Deployment/Infrastructure

## Testing Done

Describe the tests you've done:

- [ ] Unit tests added/updated
- [ ] Integration tests added/updated
- [ ] Manual testing performed
- [ ] Cross-browser testing (if UI changes)
- [ ] Mobile responsiveness verified (if UI changes)

## Security Considerations

For changes involving data or authentication:

- [ ] No sensitive data is exposed
- [ ] Authentication checks are in place
- [ ] Input validation is implemented
- [ ] Rate limiting is considered (if applicable)

## Checklist

- [ ] I have read the [CONTRIBUTING](https://github.com/Mail-0/Zero/blob/staging/.github/CONTRIBUTING.md) document
- [ ] My code follows the project's style guidelines
- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in complex areas
- [ ] I have updated the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix/feature works
- [ ] All tests pass locally
- [ ] Any dependent changes are merged and published

## Additional Notes

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## Screenshots/Recordings

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---

_By submitting this pull request, I confirm that my contribution is made under the terms of the project's license._

    
<!-- This is an auto-generated description by cubic. -->
---

## Summary by cubic
Added automatic retry logic for Gmail API rate limit errors to reduce sync failures and improve reliability.

- **Bug Fixes**
  - Detects Gmail rate limit errors and retries failed requests up to 10 times with a 60-second delay between attempts.

<!-- End of auto-generated description by cubic. -->

Author: MrgSub

apps/server/src/lib/gmail-rate-limit.ts

@@ -0,0 +1,43 @@
+import { Effect, Duration, Schedule } from 'effect';
+
+/**
+ * Gmail signals per-user quota problems in two ways:
+ *  – HTTP 429 Too Many Requests
+ *  – HTTP 403 with reason == userRateLimitExceeded or quotaExceeded
+ */
+export function isGmailRateLimit(err: unknown): boolean {
+  const e: any = err || {};
+  const status = e.code ?? e.status ?? e.response?.status;
+  
+  if (status === 429) return true;
+  if (status === 403) {
+    const errors = e.errors ?? 
+                   e.response?.data?.error?.errors ?? 
+                   [];
+    return errors.some((x: any) =>
+      ['userRateLimitExceeded', 'rateLimitExceeded', 'quotaExceeded',
+       'dailyLimitExceeded', 'backendError', 'limitExceeded'].includes(x.reason)
+    );
+  }
+  return false;
+}
+
+/**
+ * A schedule that:
+ *  – retries while the error *is* a rate-limit error (max 10 attempts)
+ *  – waits 60 seconds between retries (conservative for Gmail user quotas)
+ *  – stops immediately for any other error
+ */
+export const gmailRateLimitSchedule = Schedule
+  .recurWhile(isGmailRateLimit)
+  .pipe(Schedule.intersect(Schedule.recurs(10)))  // max 10 attempts
+  .pipe(Schedule.addDelay(() => Duration.seconds(60)));  // 60s delay between retries
+
+/**
+ * Generic wrapper that applies the schedule
+ */
+export function withGmailRetry<A>(
+  eff: Effect.Effect<A, unknown, never>,
+): Effect.Effect<A, unknown, never> {
+  return eff.pipe(Effect.retry(gmailRateLimitSchedule));
+}

apps/server/src/routes/chat.ts

@@ -47,6 +47,8 @@ import { McpAgent } from 'agents/mcp';
 
 import { createDb } from '../db';
 import { z } from 'zod';
+import { Effect } from 'effect';
+import { withGmailRetry } from '../lib/gmail-rate-limit';
 
 const decoder = new TextDecoder();
 
@@ -881,7 +883,7 @@ export class ZeroAgent extends AIChatAgent<typeof env> {
     this.syncThreadsInProgress.set(threadId, true);
 
     try {
-      const threadData = await this.driver.get(threadId);
+      const threadData = await this.getWithRetry(threadId);
       const latest = threadData.latest;
 
       if (latest) {
@@ -935,6 +937,26 @@ export class ZeroAgent extends AIChatAgent<typeof env> {
     return `${this.name}/${threadId}.json`;
   }
 
+  private async listWithRetry(params: Parameters<MailManager['list']>[0]) {
+    if (!this.driver) throw new Error('No driver available');
+
+    return Effect.runPromise(
+      withGmailRetry(
+        Effect.tryPromise(() => this.driver!.list(params))
+      ),
+    );
+  }
+
+  private async getWithRetry(threadId: string): Promise<IGetThreadResponse> {
+    if (!this.driver) throw new Error('No driver available');
+
+    return Effect.runPromise(
+      withGmailRetry(
+        Effect.tryPromise(() => this.driver!.get(threadId))
+      ),
+    );
+  }
+
   async syncThreads(folder: string) {
     if (!this.driver) {
       console.error('No driver available for syncThreads');
@@ -963,7 +985,7 @@ export class ZeroAgent extends AIChatAgent<typeof env> {
       while (hasMore) {
         _pageCount++;
 
-        const result = await this.driver.list({
+        const result = await this.listWithRetry({
           folder,
           maxResults: maxCount,
           pageToken: pageToken || undefined,