diff --git a/src/services/sqlite/SessionStore.ts b/src/services/sqlite/SessionStore.ts
index a234a518..07df86d2 100644
--- a/src/services/sqlite/SessionStore.ts
+++ b/src/services/sqlite/SessionStore.ts
@@ -889,6 +889,16 @@ export class SessionStore {
     `).run(memorySessionId, sessionDbId);
   }
 
+  markSessionCompleted(sessionDbId: number): void {
+    const nowEpoch = Date.now();
+    const nowIso = new Date(nowEpoch).toISOString();
+    this.db.prepare(`
+      UPDATE sdk_sessions
+      SET status = 'completed', completed_at = ?, completed_at_epoch = ?
+      WHERE id = ?
+    `).run(nowIso, nowEpoch, sessionDbId);
+  }
+
   /**
    * Ensures memory_session_id is registered in sdk_sessions before FK-constrained INSERT.
    * This fixes Issue #846 where observations fail after worker restart because the
diff --git a/src/services/worker/http/routes/SessionRoutes.ts b/src/services/worker/http/routes/SessionRoutes.ts
index 9db84dc2..5bd3de87 100644
--- a/src/services/worker/http/routes/SessionRoutes.ts
+++ b/src/services/worker/http/routes/SessionRoutes.ts
@@ -40,7 +40,8 @@ export class SessionRoutes extends BaseRouteHandler {
     super();
     this.completionHandler = new SessionCompletionHandler(
       sessionManager,
-      eventBroadcaster
+      eventBroadcaster,
+      dbManager.getSessionStore()
     );
   }
 
diff --git a/src/services/worker/session/SessionCompletionHandler.ts b/src/services/worker/session/SessionCompletionHandler.ts
index eaba24d1..9ed896e8 100644
--- a/src/services/worker/session/SessionCompletionHandler.ts
+++ b/src/services/worker/session/SessionCompletionHandler.ts
@@ -11,12 +11,14 @@
 
 import { SessionManager } from '../SessionManager.js';
 import { SessionEventBroadcaster } from '../events/SessionEventBroadcaster.js';
+import { SessionStore } from '../../sqlite/SessionStore.js';
 import { logger } from '../../../utils/logger.js';
 
 export class SessionCompletionHandler {
   constructor(
     private sessionManager: SessionManager,
-    private eventBroadcaster: SessionEventBroadcaster
+    private eventBroadcaster: SessionEventBroadcaster,
+    private sessionStore: SessionStore
   ) {}
 
   /**
@@ -24,6 +26,9 @@ export class SessionCompletionHandler {
    * Used by DELETE /api/sessions/:id and POST /api/sessions/:id/complete
    */
   async completeByDbId(sessionDbId: number): Promise<void> {
+    // Persist completion to database before in-memory cleanup (fix for #1532)
+    this.sessionStore.markSessionCompleted(sessionDbId);
+
     // Delete from session manager (aborts SDK agent via SIGTERM)
     await this.sessionManager.deleteSession(sessionDbId);
 
diff --git a/tests/services/sqlite/session-store-mark-completed.test.ts b/tests/services/sqlite/session-store-mark-completed.test.ts
new file mode 100644
index 00000000..36e3ff5b
--- /dev/null
+++ b/tests/services/sqlite/session-store-mark-completed.test.ts
@@ -0,0 +1,66 @@
+/**
+ * Tests for SessionStore.markSessionCompleted (fix for #1532)
+ *
+ * Mock Justification: NONE (0% mock code)
+ * - Uses real SQLite with ':memory:' - tests actual SQL and schema
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'bun:test';
+import { SessionStore } from '../../../src/services/sqlite/SessionStore.js';
+
+describe('SessionStore.markSessionCompleted', () => {
+  let store: SessionStore;
+
+  beforeEach(() => {
+    store = new SessionStore(':memory:');
+  });
+
+  afterEach(() => {
+    store.close();
+  });
+
+  it('sets status to completed and records completed_at timestamps', () => {
+    const before = Date.now();
+    const id = store.createSDKSession('session-1', 'project', 'prompt');
+
+    store.markSessionCompleted(id);
+
+    const row = store.db.prepare(
+      'SELECT status, completed_at, completed_at_epoch FROM sdk_sessions WHERE id = ?'
+    ).get(id) as { status: string; completed_at: string; completed_at_epoch: number };
+
+    expect(row.status).toBe('completed');
+    expect(row.completed_at).toBeTruthy();
+    expect(row.completed_at_epoch).toBeGreaterThanOrEqual(before);
+    expect(row.completed_at_epoch).toBeLessThanOrEqual(Date.now());
+  });
+
+  it('leaves other sessions unaffected', () => {
+    const id1 = store.createSDKSession('session-a', 'project', 'prompt');
+    const id2 = store.createSDKSession('session-b', 'project', 'prompt');
+
+    store.markSessionCompleted(id1);
+
+    const row2 = store.db.prepare(
+      'SELECT status, completed_at FROM sdk_sessions WHERE id = ?'
+    ).get(id2) as { status: string; completed_at: string | null };
+
+    expect(row2.status).toBe('active');
+    expect(row2.completed_at).toBeNull();
+  });
+
+  it('does not throw when called on a non-existent session id', () => {
+    expect(() => store.markSessionCompleted(99999)).not.toThrow();
+  });
+
+  it('completed_at is a valid ISO timestamp', () => {
+    const id = store.createSDKSession('session-iso', 'project', 'prompt');
+    store.markSessionCompleted(id);
+
+    const row = store.db.prepare(
+      'SELECT completed_at FROM sdk_sessions WHERE id = ?'
+    ).get(id) as { completed_at: string };
+
+    expect(() => new Date(row.completed_at).toISOString()).not.toThrow();
+    expect(new Date(row.completed_at).getTime()).toBeGreaterThan(0);
+  });
+});