test(acp): await cancelled tool updates

packages/support/acp-snapshot/tests/fixtures/fake-acp-agent.ts

@@ -35,6 +35,8 @@ interface Behavior {
   prompt?: 'respond' | 'error' | 'hang-until-cancel'
   /** Emit a tool call instead of a message chunk before parking a cancellable prompt. */
   cancelAtToolCall?: boolean
+  /** Emit the parked tool call's terminal update after answering cancellation. */
+  cancelToolCallUpdate?: boolean
   /** Before responding to a prompt, send a `session/request_permission` request and echo its outcome as a chunk. */
   permissionProbe?: boolean
   /** Echo the `DSH_SNAPSHOT_*` env the harness set as a chunk (spec-side env-plumbing assertions). */
@@ -247,6 +249,19 @@ function handleFrame(frame: Record<string, unknown>): void {
         const parked = parkedPromptId
         parkedPromptId = null
         respond(parked, { stopReason: 'cancelled' })
+        if (behavior.cancelToolCallUpdate === true) {
+          send({
+            method: 'session/update',
+            params: {
+              sessionId,
+              update: {
+                sessionUpdate: 'tool_call_update',
+                toolCallId: 'call_fake_1',
+                status: 'failed',
+              },
+            },
+          })
+        }
       }
       return
     default:

packages/support/acp-snapshot/tests/harness.spec.ts

@@ -334,14 +334,26 @@ describe('runScenario', () => {
     expect(result.rawStdout.indexOf('thinking about it')).toBeLessThan(result.rawStdout.indexOf('cancelled'))
   })
 
-  it('promptAndCancel can wait for a tool call before cancelling', { timeout: 20_000 }, async () => {
-    const { fixtureFile } = await scenario({ prompt: 'hang-until-cancel', cancelAtToolCall: true })
+  it('promptAndCancel can bracket cancellation with tool-call updates', { timeout: 20_000 }, async () => {
+    const { fixtureFile } = await scenario({
+      prompt: 'hang-until-cancel',
+      cancelAtToolCall: true,
+      cancelToolCallUpdate: true,
+    })
     const result = await runScenario(
-      { steps: [...boot, { op: 'promptAndCancel', text: 'hang', afterUpdate: 'tool_call' }] },
+      {
+        steps: [...boot, {
+          op: 'promptAndCancel',
+          text: 'hang',
+          afterUpdate: 'tool_call',
+          waitForToolCallUpdate: 'call_fake_1',
+        }],
+      },
       { agent: AGENT, mode: 'replay', fixtureFile },
     )
     expect(result.rawStdout).toContain('"sessionUpdate":"tool_call"')
     expect(result.rawStdout.indexOf('"sessionUpdate":"tool_call"')).toBeLessThan(result.rawStdout.indexOf('cancelled'))
+    expect(result.rawStdout.indexOf('cancelled')).toBeLessThan(result.rawStdout.indexOf('"sessionUpdate":"tool_call_update"'))
   })
 
   it('promptExpectError swallows a model-error response as the expected outcome', { timeout: 20_000 }, async () => {