diff --git a/.changeset/pretooluse-abort-fail-closed.md b/.changeset/pretooluse-abort-fail-closed.md
new file mode 100644
index 00000000..67454498
--- /dev/null
+++ b/.changeset/pretooluse-abort-fail-closed.md
@@ -0,0 +1,5 @@
+---
+"@openrouter/agent": patch
+---
+
+Fail closed when a blocking hook chain is aborted. If a `PreToolUse` or `UserPromptSubmit` chain stops early because its signal was aborted (an `asyncTimeout` on detached work expiring, or `abortInflight()`), the emit result now reports `blocked: true` instead of `blocked: false`, so handlers that never ran (for example a later deny guard) can no longer be skipped into an approval.
diff --git a/packages/agent/src/lib/hooks-emit.ts b/packages/agent/src/lib/hooks-emit.ts
index a3c6eaef..7a050717 100644
--- a/packages/agent/src/lib/hooks-emit.ts
+++ b/packages/agent/src/lib/hooks-emit.ts
@@ -65,7 +65,8 @@ function isPlainMutableObject(value: unknown): value is Record<string, unknown>
  * - Cooperative abort via `context.signal`: the chain checks
  *   `signal.aborted` between handlers and bails out when set so
  *   `abortInflight()` has a deterministic effect on the chain itself (not just
- *   on handlers that happen to consult the signal).
+ *   on handlers that happen to consult the signal). For hooks with a block
+ *   field, bailing out before every handler ran reports `blocked: true`.
  *
  * Payload isolation: the initial payload is shallow-cloned before entering the
  * chain so mutation piping (via {@link HOOK_BEHAVIOR}) doesn't mutate the
@@ -109,6 +110,12 @@ export async function executeHandlerChain<P, R>(
     // Checked before each handler so synchronous chains stop promptly instead
     // of running to completion with only advisory notice to each handler.
     if (context.signal.aborted) {
+      // A hook that can block (PreToolUse, UserPromptSubmit) fails closed:
+      // the handlers left unrun may include the guard that would have
+      // blocked, so an aborted chain must not read as an approval.
+      if (behavior?.blockField) {
+        blocked = true;
+      }
       break;
     }
 
diff --git a/packages/agent/src/lib/hooks-types.ts b/packages/agent/src/lib/hooks-types.ts
index 6cfb99a7..55a95f4e 100644
--- a/packages/agent/src/lib/hooks-types.ts
+++ b/packages/agent/src/lib/hooks-types.ts
@@ -120,7 +120,11 @@ export interface EmitResult<R, P> {
   readonly pending: Promise<void>[];
   /** The payload after all mutation piping has been applied. */
   readonly finalPayload: P;
-  /** True if any handler triggered a block/reject short-circuit. */
+  /**
+   * True if any handler triggered a block/reject short-circuit, or if the
+   * chain of a blocking hook (PreToolUse, UserPromptSubmit) was aborted
+   * before every handler ran.
+   */
   readonly blocked: boolean;
   /**
    * True if any handler's result actually piped a mutation into the payload
diff --git a/packages/agent/tests/unit/hooks-contract-fixes.test.ts b/packages/agent/tests/unit/hooks-contract-fixes.test.ts
index 6fde4667..e9d5885e 100644
--- a/packages/agent/tests/unit/hooks-contract-fixes.test.ts
+++ b/packages/agent/tests/unit/hooks-contract-fixes.test.ts
@@ -382,3 +382,140 @@ describe('asyncTimeout and abortInflight semantics', () => {
     expect(signal?.aborted).toBe(false);
   });
 });
+
+describe('blocking hooks fail closed when the chain is aborted', () => {
+  function registerTimeoutThenGuard(manager: HooksManager, guard: () => void) {
+    manager.on('PreToolUse', {
+      handler: () => ({
+        async: true as const,
+        work: new Promise<never>(() => {}),
+        asyncTimeout: 10,
+      }),
+    });
+    manager.on('PreToolUse', {
+      handler: () => new Promise<void>((resolve) => setTimeout(resolve, 50)),
+    });
+    manager.on('PreToolUse', {
+      handler: () => {
+        guard();
+        return {
+          block: 'policy forbids this call',
+        };
+      },
+    });
+  }
+
+  it('reports PreToolUse as blocked when a detached timeout skips a later guard', async () => {
+    vi.useFakeTimers();
+    vi.spyOn(console, 'warn').mockImplementation(() => {});
+    const manager = new HooksManager();
+    const guard = vi.fn();
+    registerTimeoutThenGuard(manager, guard);
+
+    const pending = manager.emit(
+      'PreToolUse',
+      {
+        toolName: 't',
+        toolInput: {},
+      },
+      {
+        toolName: 't',
+      },
+    );
+    await vi.advanceTimersByTimeAsync(60);
+    const result = await pending;
+
+    expect(guard).not.toHaveBeenCalled();
+    expect(result.blocked).toBe(true);
+  });
+
+  it('reports PreToolUse as blocked when abortInflight() fires mid-chain', async () => {
+    const manager = new HooksManager();
+    const guard = vi.fn();
+    manager.on('PreToolUse', {
+      handler: () => {
+        manager.abortInflight('shutdown');
+      },
+    });
+    manager.on('PreToolUse', {
+      handler: () => {
+        guard();
+        return {
+          block: 'policy forbids this call',
+        };
+      },
+    });
+
+    const result = await manager.emit(
+      'PreToolUse',
+      {
+        toolName: 't',
+        toolInput: {},
+      },
+      {
+        toolName: 't',
+      },
+    );
+
+    expect(guard).not.toHaveBeenCalled();
+    expect(result.blocked).toBe(true);
+  });
+
+  it('still runs every PreToolUse handler when detached work settles in time', async () => {
+    const manager = new HooksManager();
+    const guard = vi.fn();
+    manager.on('PreToolUse', {
+      handler: () => ({
+        async: true as const,
+        work: Promise.resolve(),
+        asyncTimeout: 10,
+      }),
+    });
+    manager.on('PreToolUse', {
+      handler: () => {
+        guard();
+      },
+    });
+
+    const result = await manager.emit(
+      'PreToolUse',
+      {
+        toolName: 't',
+        toolInput: {},
+      },
+      {
+        toolName: 't',
+      },
+    );
+
+    expect(guard).toHaveBeenCalledOnce();
+    expect(result.blocked).toBe(false);
+  });
+
+  it('does not mark non-blocking hooks as blocked when aborted', async () => {
+    const manager = new HooksManager();
+    manager.on('PostToolUse', {
+      handler: () => {
+        manager.abortInflight('shutdown');
+      },
+    });
+    manager.on('PostToolUse', {
+      handler: () => {},
+    });
+
+    const result = await manager.emit(
+      'PostToolUse',
+      {
+        toolName: 't',
+        toolInput: {},
+        toolOutput: null,
+        durationMs: 1,
+      },
+      {
+        toolName: 't',
+      },
+    );
+
+    expect(result.blocked).toBe(false);
+  });
+});