fix: prevent unbounded Map growth in chats server

[drewburchfield]

Summary

Three Maps in the chats server grow without bounds, causing memory exhaustion in long-running deployments:

• conversationMessageCounts and conversationMessageSnapshots in chats-mobile.js retain entries for deleted conversations
• fileActivity and typingTimeout in FileWatcher.js accumulate stale entries
• DataCache.js cache size (50) causes thrashing with 800+ conversations

Changes

chats-mobile.js: Remove Map entries for conversations that no longer exist during loadInitialData().

DataCache.js: Increase maxCacheSize from 50 to 500. Extend TTLs to reduce cache misses.

FileWatcher.js: Add periodic cleanup (every 5 minutes) of file activity entries older than 10 minutes.

Test Plan

• [ ] Start server with 500+ conversations
• [ ] Monitor memory usage over 30+ minutes
• [ ] Delete several conversations while server runs
• [ ] Verify Map sizes stabilize (check via conversationMessageCounts.size in logs)

---

Summary by cubic

Prevents unbounded Map growth in the chats server to stop memory leaks and stabilize long-running deployments. Adds cleanup for stale entries and tunes cache settings to reduce eviction thrash.

• Bug Fixes

  • Remove conversationMessageCounts and conversationMessageSnapshots entries for deleted conversations during loadInitialData().
  • Add a 5-minute cleanup to purge stale fileActivity (>10 min) and clear orphaned typingTimeouts.

• Performance

  • Increase DataCache maxCacheSize to 500 and extend TTLs to reduce cache evictions with large (800+ ) conversation sets.

^{Written for commit debc6452fc3f3ee0ed31d9939a3083cf50a5f86b. Summary will update automatically on new commits.}

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