diff --git a/packages/api/src/agents/background.shutdown.spec.ts b/packages/api/src/agents/background.shutdown.spec.ts
index 83d1684b029..b5b69d77d0b 100644
--- a/packages/api/src/agents/background.shutdown.spec.ts
+++ b/packages/api/src/agents/background.shutdown.spec.ts
@@ -194,6 +194,39 @@ describe('background task shutdown', () => {
       expect(summary).toEqual({ tracked: 1, interrupted: 1, flushed: 1, unsettled: 1 });
     });
 
+    it('does not retain an unconfirmed result after its task expires', async () => {
+      const registry = new BackgroundTaskRegistryClass();
+      const task = createTask(registry, 'unconfirmed-expired');
+      const controlled = controlledHandle();
+      registry.trackShutdown(task, controlled.handle);
+      registry.fail('shutdown-owner', 'shutdown-conversation', task.id, 'no durable write');
+      const now = jest.spyOn(Date, 'now').mockReturnValue(task.updatedAt + 60 * 60 * 1000 + 1);
+      try {
+        expect(registry.get('shutdown-owner', 'shutdown-conversation', task.id)).toBeUndefined();
+      } finally {
+        now.mockRestore();
+      }
+
+      expect((await registry.drainForShutdown(drainOptions())).tracked).toBe(0);
+    });
+
+    it('does not retain an unconfirmed result after capacity pressure evicts its task', async () => {
+      const registry = new BackgroundTaskRegistryClass();
+      const task = createTask(registry, 'unconfirmed-evicted');
+      const controlled = controlledHandle();
+      registry.trackShutdown(task, controlled.handle);
+      registry.fail('shutdown-owner', 'shutdown-conversation', task.id, 'no durable write');
+      task.updatedAt = Date.now() - 1_000;
+      for (let i = 0; i < 199; i++) {
+        const settled = createTask(registry, `completed-${i}`);
+        registry.complete('shutdown-owner', 'shutdown-conversation', settled.id, { content: 'ok' });
+      }
+      createTask(registry, 'trigger-eviction');
+
+      expect(registry.get('shutdown-owner', 'shutdown-conversation', task.id)).toBeUndefined();
+      expect((await registry.drainForShutdown(drainOptions())).tracked).toBe(0);
+    });
+
     it('stops tracking a task once its result is durable', async () => {
       const registry = new BackgroundTaskRegistryClass();
       const controlled = controlledHandle();
diff --git a/packages/api/src/agents/background.ts b/packages/api/src/agents/background.ts
index 700a33e7302..f98f0b3406b 100644
--- a/packages/api/src/agents/background.ts
+++ b/packages/api/src/agents/background.ts
@@ -887,6 +887,12 @@ export class BackgroundTaskRegistryClass {
     return `${userId}::${conversationId}`;
   }
 
+  private releaseEvictedShutdownHandle(task: BackgroundTask): void {
+    if (this.shutdownHandles.delete(task)) {
+      logger.warn(`[background] Unconfirmed shutdown result for evicted task ${task.id}.`);
+    }
+  }
+
   private sweepBucketTasks(bucket: TaskBucket, now: number): void {
     for (const [taskId, task] of bucket.tasks) {
       if (
@@ -895,6 +901,7 @@ export class BackgroundTaskRegistryClass {
         now - task.updatedAt > COMPLETED_TASK_TTL_MS
       ) {
         bucket.tasks.delete(taskId);
+        this.releaseEvictedShutdownHandle(task);
       }
     }
     /** Drop dedupe mappings whose task was evicted (keys are
@@ -925,6 +932,9 @@ export class BackgroundTaskRegistryClass {
           (task) => task.status === 'running' || task.completionPersistencePending === true,
         )
       ) {
+        for (const task of bucket.tasks.values()) {
+          this.releaseEvictedShutdownHandle(task);
+        }
         this.buckets.delete(bucketKey);
         continue;
       }
@@ -1079,6 +1089,7 @@ export class BackgroundTaskRegistryClass {
     const touched = new Set<TaskBucket>();
     for (const [task, bucket] of selected) {
       bucket.tasks.delete(task.id);
+      this.releaseEvictedShutdownHandle(task);
       touched.add(bucket);
     }
     const now = Date.now();
diff --git a/packages/api/src/agents/handlers.shutdown.spec.ts b/packages/api/src/agents/handlers.shutdown.spec.ts
index fb9d6d1a004..408d04092c6 100644
--- a/packages/api/src/agents/handlers.shutdown.spec.ts
+++ b/packages/api/src/agents/handlers.shutdown.spec.ts
@@ -234,6 +234,221 @@ describe('createToolExecuteHandler — background tasks at shutdown', () => {
     );
   });
 
+  it('waits for a legacy pre-admitted completion projection before declaring shutdown durable', async () => {
+    const { createToolExecuteHandler, registry } = loadModules();
+    let notifyFlush: () => void = () => undefined;
+    const flushStarted = new Promise<void>((resolve) => {
+      notifyFlush = resolve;
+    });
+    const trackShutdown = registry.trackShutdown.bind(registry);
+    jest.spyOn(registry, 'trackShutdown').mockImplementation((task, handle) =>
+      trackShutdown(task, {
+        ...handle,
+        flush: (reason) => {
+          notifyFlush();
+          return handle.flush(reason);
+        },
+      }),
+    );
+    let resolveProjection: (persisted: boolean) => void = () => undefined;
+    const persist = jest.fn(
+      () =>
+        new Promise<boolean>((resolve) => {
+          resolveProjection = resolve;
+        }),
+    );
+    const retire = jest.fn(async () => true);
+    const tool = {
+      name: 'search_mcp_docs',
+      description: 'search docs',
+      schema: z.object({ q: z.string() }),
+      invoke: jest.fn(async () => ({ content: 'legacy projection result' })),
+    } as unknown as StructuredToolInterface;
+    const handler = createToolExecuteHandler({
+      loadTools: async () => ({ loadedTools: [tool] }),
+      backgroundToolCompletion: {
+        preregister: jest.fn(async () => ({ renew: async () => true, retire })),
+        persist,
+        claim: jest.fn(async () => ({ status: 'acquired' as const, results: [] })),
+      },
+    });
+
+    await runBatch(handler, {
+      toolCalls: [
+        {
+          id: 'call-legacy-projection',
+          name: tool.name,
+          args: { q: 'legacy', run_in_background: true },
+          stepId: 'step-legacy',
+        },
+      ],
+      configurable: buildConfig([tool.name]),
+      metadata: { thread_id: 'shutdown_convo', run_id: 'response-legacy-projection' },
+    });
+    await flushMicrotasks();
+    expect(persist).toHaveBeenCalledTimes(1);
+
+    const draining = registry.drainForShutdown({
+      ...drainOptions(),
+      deadlineAt: Date.now() + 1_750,
+      flushReserveMs: 1_400,
+    });
+    let drained = false;
+    void draining.then(() => {
+      drained = true;
+    });
+    await flushStarted;
+    await flushMicrotasks();
+    expect(drained).toBe(false);
+    resolveProjection(true);
+    expect(await draining).toEqual({ tracked: 1, interrupted: 0, flushed: 1, unsettled: 0 });
+    expect(retire).not.toHaveBeenCalled();
+  });
+
+  it('reports a pre-admitted legacy completion with no durable projection as unsettled', async () => {
+    const { createToolExecuteHandler, registry } = loadModules();
+    const persist = jest.fn(async () => false);
+    const tool = {
+      name: 'search_mcp_docs',
+      description: 'search docs',
+      schema: z.object({ q: z.string() }),
+      invoke: jest.fn(async () => ({ content: 'missing legacy result' })),
+    } as unknown as StructuredToolInterface;
+    const handler = createToolExecuteHandler({
+      loadTools: async () => ({ loadedTools: [tool] }),
+      backgroundToolCompletion: {
+        preregister: jest.fn(async () => ({ renew: async () => true, retire: async () => true })),
+        persist,
+        claim: jest.fn(async () => ({ status: 'acquired' as const, results: [] })),
+      },
+    });
+
+    await runBatch(handler, {
+      toolCalls: [
+        {
+          id: 'call-legacy-failed',
+          name: tool.name,
+          args: { q: 'failed', run_in_background: true },
+          stepId: 'step-legacy-failed',
+        },
+      ],
+      configurable: buildConfig([tool.name]),
+      metadata: { thread_id: 'shutdown_convo', run_id: 'response-legacy-failed' },
+    });
+    await flushMicrotasks();
+    expect(persist).toHaveBeenCalledTimes(1);
+    expect(
+      await registry.drainForShutdown({
+        ...drainOptions(),
+        deadlineAt: Date.now() + 190,
+        interruptGraceMs: 75,
+        flushReserveMs: 40,
+      }),
+    ).toEqual({
+      tracked: 1,
+      interrupted: 0,
+      flushed: 1,
+      unsettled: 1,
+    });
+  });
+
+  it('projects an interrupted result for an uncooperative legacy completion without a receipt', async () => {
+    const { createToolExecuteHandler, registry } = loadModules();
+    const persist = jest.fn(async () => true);
+    const controlled = controlledTool({ honorAbort: false });
+    const handler = createToolExecuteHandler({
+      loadTools: async () => ({ loadedTools: [controlled.tool] }),
+      backgroundToolCompletion: {
+        preregister: jest.fn(async () => ({ renew: async () => true, retire: async () => true })),
+        persist,
+        claim: jest.fn(async () => ({ status: 'acquired' as const, results: [] })),
+      },
+    });
+
+    await runBatch(handler, {
+      toolCalls: [
+        {
+          id: 'call-legacy-stubborn',
+          name: controlled.tool.name,
+          args: { q: 'stubborn', run_in_background: true },
+          stepId: 'step-legacy-stubborn',
+        },
+      ],
+      configurable: buildConfig([controlled.tool.name]),
+      metadata: { thread_id: 'shutdown_convo', run_id: 'response-legacy-stubborn' },
+    });
+
+    expect(
+      await registry.drainForShutdown({
+        ...drainOptions(),
+        deadlineAt: Date.now() + 280,
+        interruptGraceMs: 90,
+        flushReserveMs: 70,
+      }),
+    ).toEqual({
+      tracked: 1,
+      interrupted: 1,
+      flushed: 1,
+      unsettled: 0,
+    });
+    expect(persist).toHaveBeenCalledWith(
+      expect.objectContaining({
+        output: interruptedOutput,
+        backgroundTask: expect.objectContaining({ status: 'error' }),
+      }),
+    );
+
+    controlled.resolve('late success');
+    await flushMicrotasks();
+    await flushMicrotasks();
+    expect(persist).toHaveBeenCalledTimes(1);
+  });
+
+  it('reports a failed legacy interruption projection as unconfirmed', async () => {
+    const { createToolExecuteHandler, registry } = loadModules();
+    const persist = jest.fn(async () => false);
+    const controlled = controlledTool({ honorAbort: false });
+    const handler = createToolExecuteHandler({
+      loadTools: async () => ({ loadedTools: [controlled.tool] }),
+      backgroundToolCompletion: {
+        preregister: jest.fn(async () => ({ renew: async () => true, retire: async () => true })),
+        persist,
+        claim: jest.fn(async () => ({ status: 'acquired' as const, results: [] })),
+      },
+    });
+
+    await runBatch(handler, {
+      toolCalls: [
+        {
+          id: 'call-legacy-interruption-failed',
+          name: controlled.tool.name,
+          args: { q: 'stubborn', run_in_background: true },
+          stepId: 'step-legacy-interruption-failed',
+        },
+      ],
+      configurable: buildConfig([controlled.tool.name]),
+      metadata: { thread_id: 'shutdown_convo', run_id: 'response-legacy-interruption-failed' },
+    });
+
+    expect(
+      await registry.drainForShutdown({
+        ...drainOptions(),
+        deadlineAt: Date.now() + 280,
+        interruptGraceMs: 90,
+        flushReserveMs: 70,
+      }),
+    ).toEqual({
+      tracked: 1,
+      interrupted: 1,
+      flushed: 1,
+      unsettled: 1,
+    });
+    expect(persist).toHaveBeenCalledTimes(1);
+    controlled.resolve('late success');
+    await flushMicrotasks();
+    await flushMicrotasks();
+  });
+
   it('waits for the projected result when an independent receipt write returns false', async () => {
     const { createToolExecuteHandler, registry } = loadModules();
     const adapter = completionAdapter();
diff --git a/packages/api/src/agents/handlers.ts b/packages/api/src/agents/handlers.ts
index ab892079b74..9303dfaf948 100644
--- a/packages/api/src/agents/handlers.ts
+++ b/packages/api/src/agents/handlers.ts
@@ -5963,6 +5963,7 @@ export function createToolExecuteHandler(options: ToolExecuteOptions): EventHand
                 let durableReceiptWrite: Promise<boolean> | undefined;
                 let durableReceiptAmbiguous = false;
                 let durableResultConfirmed = false;
+                let forcedShutdownResult = false;
                 let resolveDurableReceipt: () => void = () => undefined;
                 const durableReceiptSettled = new Promise<void>((resolve) => {
                   resolveDurableReceipt = resolve;
@@ -6306,11 +6307,17 @@ export function createToolExecuteHandler(options: ToolExecuteOptions): EventHand
                     );
                   }
                 };
-                const persistSettledBackgroundResult = async (params: {
-                  output?: string;
-                  artifact?: unknown;
-                  status: 'completed' | 'error' | 'cancelled';
-                }): Promise<void> => {
+                const persistSettledBackgroundResult = async (
+                  params: {
+                    output?: string;
+                    artifact?: unknown;
+                    status: 'completed' | 'error' | 'cancelled';
+                  },
+                  forced = false,
+                ): Promise<void> => {
+                  if (forcedShutdownResult && !forced) {
+                    return;
+                  }
                   settledReceipt = { status: params.status, output: params.output };
                   /** Held for the whole persist, including a code harvest that waits for
                    *  a long dispatch turn, so retention pressure cannot evict the task. */
@@ -6671,7 +6678,7 @@ export function createToolExecuteHandler(options: ToolExecuteOptions): EventHand
                 })();
                 void settlement.then(
                   () => {
-                    if (completionAdmission?.persistResult == null || !completionPreregistered) {
+                    if (completionAdmission == null || !completionPreregistered) {
                       resolveDurableReceipt();
                     }
                   },
@@ -6693,6 +6700,7 @@ export function createToolExecuteHandler(options: ToolExecuteOptions): EventHand
                     } else if (settledReceipt != null) {
                       await writeDurableReceipt({ ...settledReceipt, settledAt: new Date() });
                     } else {
+                      forcedShutdownResult = true;
                       const failure = toBackgroundToolFailure(tc.name, reason);
                       backgroundTaskRegistry.fail(
                         backgroundUserId,
@@ -6709,22 +6717,31 @@ export function createToolExecuteHandler(options: ToolExecuteOptions): EventHand
                           detachedError,
                         );
                       }
-                      await writeDurableReceipt({
-                        status: 'error',
-                        output: failure,
-                        settledAt: new Date(),
-                      });
+                      if (completionAdmission?.persistResult != null) {
+                        await writeDurableReceipt({
+                          status: 'error',
+                          output: failure,
+                          settledAt: new Date(),
+                        });
+                      } else if (completionAdmission != null) {
+                        await persistSettledBackgroundResult(
+                          { status: 'error', output: failure },
+                          true,
+                        );
+                      }
                     }
-                    if (durableResultConfirmed || completionAdmission?.persistResult == null) {
+                    if (durableResultConfirmed || completionAdmission == null) {
                       return;
                     }
-                    if (settledReceipt != null) {
+                    if (settledReceipt != null && !forcedShutdownResult) {
                       await settlement;
                       if (durableResultConfirmed) {
                         return;
                       }
                     }
-                    throw new Error(`Background task ${task.id} has no durable shutdown result`);
+                    if (completionPreregistered) {
+                      throw new Error(`Background task ${task.id} has no durable shutdown result`);
+                    }
                   },
                 });
                 if (