feat: inject file observation timeline on PreToolUse Read hook

When Claude reads a file, the PreToolUse hook queries for existing
observations about that file and injects the timeline into context
via additionalContext + permissionDecision: allow. This prevents
duplicate observations and saves tokens through active rediscovery.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/sqlite/observations/get.ts

@@ -4,6 +4,7 @@
  */
 
 import { Database } from 'bun:sqlite';
+import path from 'path';
 import { logger } from '../../../utils/logger.js';
 import type { ObservationRecord } from '../../../types/database.js';
 import type { GetObservationsByIdsOptions, ObservationSessionRow } from './types.js';
@@ -111,3 +112,42 @@ export function getObservationsForSession(
 
   return stmt.all(memorySessionId) as ObservationSessionRow[];
 }
+
+/**
+ * Get observations associated with a given file path.
+ * Searches both files_read and files_modified using basename matching
+ * to handle differing absolute paths across sessions.
+ */
+export function getObservationsByFilePath(
+  db: Database,
+  filePath: string,
+  options?: { project?: string; limit?: number }
+): ObservationRecord[] {
+  const basename = path.basename(filePath);
+  const likePattern = `%${basename}%`;
+  const limit = options?.limit ?? 30;
+
+  const additionalConditions: string[] = [];
+  const params: any[] = [likePattern, likePattern];
+
+  if (options?.project) {
+    additionalConditions.push('AND project = ?');
+    params.push(options.project);
+  }
+
+  const additionalWhere = additionalConditions.join(' ');
+
+  const stmt = db.prepare(`
+    SELECT *
+    FROM observations
+    WHERE (
+      EXISTS (SELECT 1 FROM json_each(files_read) WHERE value LIKE ?)
+      OR EXISTS (SELECT 1 FROM json_each(files_modified) WHERE value LIKE ?)
+    )
+    ${additionalWhere}
+    ORDER BY created_at_epoch DESC
+    LIMIT ${limit}
+  `);
+
+  return stmt.all(...params) as ObservationRecord[];
+}

src/services/worker/http/routes/DataRoutes.ts

@@ -18,6 +18,7 @@ import { SessionManager } from '../../SessionManager.js';
 import { SSEBroadcaster } from '../../SSEBroadcaster.js';
 import type { WorkerService } from '../../../worker-service.js';
 import { BaseRouteHandler } from '../BaseRouteHandler.js';
+import { getObservationsByFilePath } from '../../../sqlite/observations/get.js';
 
 export class DataRoutes extends BaseRouteHandler {
   constructor(
@@ -39,6 +40,7 @@ export class DataRoutes extends BaseRouteHandler {
 
     // Fetch by ID endpoints
     app.get('/api/observation/:id', this.handleGetObservationById.bind(this));
+    app.get('/api/observations/by-file', this.handleGetObservationsByFile.bind(this));
     app.post('/api/observations/batch', this.handleGetObservationsByIds.bind(this));
     app.get('/api/session/:id', this.handleGetSessionById.bind(this));
     app.post('/api/sdk-sessions/batch', this.handleGetSdkSessionsByIds.bind(this));
@@ -108,6 +110,26 @@ export class DataRoutes extends BaseRouteHandler {
     res.json(observation);
   });
 
+  /**
+   * Get observations associated with a file path
+   * GET /api/observations/by-file?path=<file_path>&project=<project>&limit=30
+   */
+  private handleGetObservationsByFile = this.wrapHandler((req: Request, res: Response): void => {
+    const filePath = req.query.path as string | undefined;
+    if (!filePath) {
+      this.badRequest(res, 'path query parameter is required');
+      return;
+    }
+
+    const project = req.query.project as string | undefined;
+    const limit = req.query.limit ? parseInt(req.query.limit as string, 10) : undefined;
+
+    const db = this.dbManager.getSessionStore().db;
+    const observations = getObservationsByFilePath(db, filePath, { project, limit });
+
+    res.json({ observations, count: observations.length });
+  });
+
   /**
    * Get observations by array of IDs
    * POST /api/observations/batch