feat: Implement user prompt syncing to Chroma and enhance timeline querying

- Added `getObservationById` method to retrieve observations by ID in SessionStore.
- Introduced `getSessionSummariesByIds` and `getUserPromptsByIds` methods for fetching session summaries and user prompts by IDs.
- Developed `getTimelineAroundTimestamp` and `getTimelineAroundObservation` methods to provide a unified timeline of observations, sessions, and prompts around a specified anchor point.
- Enhanced ChromaSync to format and sync user prompts, including a new `syncUserPrompt` method.
- Updated WorkerService to sync the latest user prompt to Chroma after updating the worker port.
- Created tests for timeline querying and MCP handler logic to ensure functionality.
- Documented the implementation plan for user prompts and timeline context tool in the Chroma search completion plan.

src/services/worker-service.ts

@@ -195,8 +195,37 @@ class WorkerService {
 
     // Update port in database
     db.setWorkerPort(sessionDbId, this.port!);
+
+    // Get the latest user_prompt for this session to sync to Chroma
+    const latestPrompt = db.db.prepare(`
+      SELECT
+        up.*,
+        s.sdk_session_id,
+        s.project
+      FROM user_prompts up
+      JOIN sdk_sessions s ON up.claude_session_id = s.claude_session_id
+      WHERE up.claude_session_id = ?
+      ORDER BY up.created_at_epoch DESC
+      LIMIT 1
+    `).get(claudeSessionId) as any;
+
     db.close();
 
+    // Sync user prompt to Chroma (fire-and-forget, but crash on failure)
+    if (latestPrompt) {
+      this.chromaSync.syncUserPrompt(
+        latestPrompt.id,
+        latestPrompt.sdk_session_id,
+        latestPrompt.project,
+        latestPrompt.prompt_text,
+        latestPrompt.prompt_number,
+        latestPrompt.created_at_epoch
+      ).catch(err => {
+        logger.failure('WORKER', 'Failed to sync user_prompt to Chroma', { promptId: latestPrompt.id }, err);
+        process.exit(1); // Fail fast - Chroma sync is critical
+      });
+    }
+
     // Start SDK agent in background
     session.generatorPromise = this.runSDKAgent(session).catch(err => {
       logger.failure('WORKER', 'SDK agent error', { sessionId: sessionDbId }, err);