diff --git a/packages/subagent/subagent/src/continuation-activation.ts b/packages/subagent/subagent/src/continuation-activation.ts
index f679397432..d5caf0a0e2 100644
--- a/packages/subagent/subagent/src/continuation-activation.ts
+++ b/packages/subagent/subagent/src/continuation-activation.ts
@@ -369,7 +369,8 @@ export class ContinuableActivationRegistry {
       activation.execution.cancel(kind, true)
     } else {
       activation.execution.controller.abort({ kind })
-      void this.dispose(activation).catch((error: unknown) => { this.reportTeardownFailure(activation, error) })
+      // The settlement observer reports teardown failures.
+      void this.dispose(activation).catch(() => undefined)
     }
   }
 
diff --git a/packages/subagent/subagent/tests/external-activation.spec.ts b/packages/subagent/subagent/tests/external-activation.spec.ts
index 2708ef49c0..6e14b61e5d 100644
--- a/packages/subagent/subagent/tests/external-activation.spec.ts
+++ b/packages/subagent/subagent/tests/external-activation.spec.ts
@@ -221,6 +221,7 @@ describe('external subagent activations', () => {
       return { ...backend.run, dispose }
     })
     const activation = await fixture.start()
+    const warning = vi.spyOn(fixture.ctx.logger, 'warn')
     const authority = kind === 'user'
       ? { kind, parentSessionId: fixture.parent.id }
       : { kind, agent: fixture.parent }
@@ -238,6 +239,7 @@ describe('external subagent activations', () => {
         const rejected = expect(disposal).rejects.toThrow('interrupt cleanup failed')
         backend.cleanup.reject(new Error('interrupt cleanup failed'))
         await rejected
+        await vi.waitFor(() => { expect(warning).toHaveBeenCalledTimes(1) })
       } else {
         backend.cleanup.resolve(undefined)
         await disposal