Fix UNIQUE constraint on events.sequence during concurrent tool calls

[alexgorbatchev]

Summary

• Restructures event persistence to assign sequence numbers atomically with the SQLite insert, then notify SSE subscribers — preventing duplicate sequences when concurrent MCP tool calls hit the HTTP server
• Adds retry loop (up to 5 attempts) on UNIQUE constraint failed: events.sequence to gracefully handle any remaining edge cases
• Adds nextSequence() and notify() methods to EventBus so SQLite-backed stores can persist before distributing

Changes

• events.ts: Split emit() into nextSequence() + notify() building blocks. emit() still works as before for non-persisted events (in-memory store, action.requested).
• sqlite.ts: Replace eventBus.emit() → persistEvent() pattern with emitAndPersist() which: assigns sequence → inserts into DB → notifies subscribers. Same for tenant store.

How it fixes the bug

Previously:

1. eventBus.emit() — increments globalSequence, notifies SSE subscribers
2. persistEvent() — inserts into SQLite

Now:

1. emitAndPersist() — increments sequence, inserts into SQLite, then notifies SSE subscribers
2. On UNIQUE violation, retries with a fresh sequence number

This ensures the sequence number in the database always matches what SSE subscribers receive, and concurrent inserts can't produce duplicates.

Fixes #138

Test plan

• Build succeeds (pnpm build in mcp/)
• Start server, create annotations, dismiss/resolve multiple concurrently from Claude Code
• Verify no UNIQUE constraint failed errors
• Verify SSE event IDs match database sequences (reconnect with Last-Event-ID works correctly)

🤖 Generated with Claude Code

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