fix: GC failed pending_messages rows at startup (Greptile iter 4)

Plan 07 deleted clearFailed/clearFailedOlderThan as "dead code", but
with the periodic sweep also removed, nothing reaps status='failed'
rows now — they accumulate indefinitely. Since claimNextMessage's
self-healing subquery scans this table, unbounded growth degrades
claim latency over time.

Re-introduces clearFailedOlderThan and calls it once at worker startup
(not a reaper — one-shot, idempotent). 7-day retention keeps enough
history for operator inspection while bounding the table.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/services/sqlite/PendingMessageStore.ts

@@ -198,6 +198,22 @@ export class PendingMessageStore {
     }
   }
 
+  /**
+   * Delete `status='failed'` rows older than `thresholdMs`. Called once at
+   * worker startup so `pending_messages` does not grow unbounded on long-
+   * running or high-failure-rate installations; `claimNextMessage`'s
+   * self-healing subquery scans this table, so bounded rows keep claim
+   * latency predictable. Not a reaper — one-shot, idempotent.
+   */
+  clearFailedOlderThan(thresholdMs: number): number {
+    const cutoff = Date.now() - thresholdMs;
+    const stmt = this.db.prepare(`
+      DELETE FROM pending_messages
+      WHERE status = 'failed' AND COALESCE(failed_at_epoch, completed_at_epoch, 0) < ?
+    `);
+    return stmt.run(cutoff).changes;
+  }
+
   /**
    * Get all pending messages for session (ordered by creation time)
    */

src/services/worker-service.ts

@@ -445,6 +445,21 @@ export class WorkerService implements WorkerRef {
       // left by a previous worker incarnation on the next claim. See
       // PATHFINDER-2026-04-22 Plan 01 Phase 3.
 
+      // One-shot GC for terminally-failed rows so pending_messages does not
+      // grow unbounded on long-running or high-failure-rate installations.
+      // Not a reaper — runs once per worker start. 7 days retains enough
+      // history for operator inspection without degrading claim latency.
+      try {
+        const { PendingMessageStore } = await import('./sqlite/PendingMessageStore.js');
+        const pendingStore = new PendingMessageStore(this.dbManager.getSessionStore().db, 3);
+        const cleared = pendingStore.clearFailedOlderThan(7 * 24 * 60 * 60 * 1000);
+        if (cleared > 0) {
+          logger.info('QUEUE', 'Startup GC cleared old failed pending_messages rows', { cleared });
+        }
+      } catch (err) {
+        logger.warn('QUEUE', 'Startup GC for failed pending_messages rows failed', {}, err instanceof Error ? err : undefined);
+      }
+
       // Initialize search services
       const formattingService = new FormattingService();
       const timelineService = new TimelineService();