diff --git a/src/cli/handlers/summarize.ts b/src/cli/handlers/summarize.ts
index 55cc6ab1..25a1f227 100644
--- a/src/cli/handlers/summarize.ts
+++ b/src/cli/handlers/summarize.ts
@@ -87,20 +87,32 @@ export const summarizeHandler: EventHandler = {
     //    This keeps the Stop hook alive (120s timeout) so the SDK agent
     //    can finish processing the summary before SessionEnd kills the session.
     const waitStart = Date.now();
+    let summaryStored: boolean | null = null;
     while ((Date.now() - waitStart) < MAX_WAIT_FOR_SUMMARY_MS) {
       await new Promise(resolve => setTimeout(resolve, POLL_INTERVAL_MS));
       try {
         const statusResponse = await workerHttpRequest(`/api/sessions/status?contentSessionId=${encodeURIComponent(sessionId)}`, {
           timeoutMs: 5000
         });
-        if (statusResponse.ok) {
-          const status = await statusResponse.json() as { queueLength?: number };
-          if ((status.queueLength ?? 0) === 0) {
-            logger.info('HOOK', 'Summary processing complete', {
+        const status = await statusResponse.json() as { queueLength?: number; summaryStored?: boolean | null };
+        const queueLength = status.queueLength ?? 0;
+        // Only treat an empty queue as completion when the session exists (non-404).
+        // A 404 means the session was not found — not that processing finished.
+        if (queueLength === 0 && statusResponse.status !== 404) {
+          summaryStored = status.summaryStored ?? null;
+          logger.info('HOOK', 'Summary processing complete', {
+            waitedMs: Date.now() - waitStart,
+            summaryStored
+          });
+          // Warn when the agent processed a summarize request but produced no storable summary.
+          // This is the silent-failure path described in #1633: queue empties but no summary record exists.
+          if (summaryStored === false) {
+            logger.warn('HOOK', 'Summary was not stored: LLM response likely lacked valid <summary> tags (#1633)', {
+              sessionId,
               waitedMs: Date.now() - waitStart
             });
-            break;
           }
+          break;
         }
       } catch {
         // Worker may be busy — keep polling
diff --git a/src/services/worker-types.ts b/src/services/worker-types.ts
index dad3444b..1a8557a0 100644
--- a/src/services/worker-types.ts
+++ b/src/services/worker-types.ts
@@ -43,6 +43,9 @@ export interface ActiveSession {
   processingMessageIds: number[];
   // Tier routing: model override per session based on queue complexity
   modelOverride?: string;
+  // Track whether the most recent storage operation persisted a summary record.
+  // Used by the status endpoint so the Stop hook can detect silent summary loss (#1633).
+  lastSummaryStored?: boolean;
 }
 
 export interface PendingMessage {
diff --git a/src/services/worker/agents/ResponseProcessor.ts b/src/services/worker/agents/ResponseProcessor.ts
index 74bd87ef..1f807302 100644
--- a/src/services/worker/agents/ResponseProcessor.ts
+++ b/src/services/worker/agents/ResponseProcessor.ts
@@ -147,6 +147,10 @@ export async function processAgentResponse(
     memorySessionId: session.memorySessionId
   });
 
+  // Track whether a summary record was stored so the status endpoint can expose this
+  // to the Stop hook for silent-summary-loss detection (#1633)
+  session.lastSummaryStored = result.summaryId !== null;
+
   // CLAIM-CONFIRM: Now that storage succeeded, confirm all processing messages (delete from queue)
   // This is the critical step that prevents message loss on generator crash
   const pendingStore = sessionManager.getPendingMessageStore();
diff --git a/src/services/worker/http/routes/SessionRoutes.ts b/src/services/worker/http/routes/SessionRoutes.ts
index 010e5c35..13828933 100644
--- a/src/services/worker/http/routes/SessionRoutes.ts
+++ b/src/services/worker/http/routes/SessionRoutes.ts
@@ -672,6 +672,9 @@ export class SessionRoutes extends BaseRouteHandler {
       status: 'active',
       sessionDbId,
       queueLength,
+      // Expose whether the last storage operation included a summary record.
+      // The Stop hook uses this to detect silent summary loss when the queue empties (#1633).
+      summaryStored: session.lastSummaryStored ?? null,
       uptime: Date.now() - session.startTime
     });
   });
diff --git a/tests/worker/agents/response-processor.test.ts b/tests/worker/agents/response-processor.test.ts
index 1638bfdb..bd7b30cb 100644
--- a/tests/worker/agents/response-processor.test.ts
+++ b/tests/worker/agents/response-processor.test.ts
@@ -683,4 +683,47 @@ describe('ResponseProcessor', () => {
       ).rejects.toThrow('Cannot store observations: memorySessionId not yet captured');
     });
   });
+
+  describe('lastSummaryStored tracking (#1633)', () => {
+    it('should set lastSummaryStored=true when storage returns a summaryId', async () => {
+      mockStoreObservations.mockImplementation(() => ({
+        observationIds: [],
+        summaryId: 42,
+        createdAtEpoch: 1700000000000,
+      } as StorageResult));
+
+      const session = createMockSession();
+      const responseText = `
+        <summary>
+          <request>user asked to fix bug</request>
+          <investigated>looked at auth module</investigated>
+          <learned>JWT tokens were expiring</learned>
+          <completed>fixed expiry check</completed>
+          <next_steps>write tests</next_steps>
+        </summary>
+      `;
+
+      await processAgentResponse(responseText, session, mockDbManager, mockSessionManager, mockWorker, 0, null, 'TestAgent');
+
+      expect(session.lastSummaryStored).toBe(true);
+    });
+
+    it('should set lastSummaryStored=false when storage returns summaryId=null (silent loss path, #1633)', async () => {
+      // Simulate the silent failure: agent returns no parseable <summary> tags,
+      // storeObservations skips summary and returns summaryId=null.
+      mockStoreObservations.mockImplementation(() => ({
+        observationIds: [],
+        summaryId: null,
+        createdAtEpoch: 1700000000000,
+      } as StorageResult));
+
+      const session = createMockSession();
+      // Response with no <summary> block — LLM failed to produce structured output
+      const responseText = '<skip_summary/>';
+
+      await processAgentResponse(responseText, session, mockDbManager, mockSessionManager, mockWorker, 0, null, 'TestAgent');
+
+      expect(session.lastSummaryStored).toBe(false);
+    });
+  });
 });