fix(e2e): reach child quiescence before temp-dir cleanup in built-bin smokes

The acp built-bin smoke killed its child and immediately rm'd the temp
consumer dir; POSIX tolerates unlinking a live process's cwd, Windows fails
EBUSY while the child still holds its cwd and session-log handles (the CI
windows job's only red step). Await the child's exit after SIGKILL and give
both smokes' rm a brief retry for the OS handle-release lag.

packages/examples/acp-demo/tests/built-bin.e2e.ts

@@ -95,8 +95,19 @@ let consumer: string | undefined
 let child: ReturnType<typeof spawn> | undefined
 
 afterEach(async () => {
-  if (child !== undefined) { child.kill('SIGKILL'); child = undefined }
-  if (consumer !== undefined) await rm(consumer, { recursive: true, force: true })
+  if (child !== undefined) {
+    const proc = child
+    child = undefined
+    // Windows retains the child's cwd and session-log handles until process
+    // teardown completes, so await exit before removing the temp directory.
+    if (proc.exitCode === null && proc.signalCode === null) {
+      const exited = new Promise<void>((resolve) => { proc.once('exit', () => { resolve() }) })
+      proc.kill('SIGKILL')
+      await exited
+    }
+  }
+  // Windows can briefly retain released handles after exit; retry removal.
+  if (consumer !== undefined) await rm(consumer, { recursive: true, force: true, maxRetries: 10, retryDelay: 100 })
   consumer = undefined
 })
 

packages/examples/stdio-demo/tests/built-bin.e2e.ts

@@ -116,7 +116,8 @@ function runBuiltBin(cwd: string, configArg: string, line: string): Promise<{ st
 let consumer: string | undefined
 
 afterEach(async () => {
-  if (consumer !== undefined) await rm(consumer, { recursive: true, force: true })
+  // Windows can briefly retain released handles after exit; retry removal.
+  if (consumer !== undefined) await rm(consumer, { recursive: true, force: true, maxRetries: 10, retryDelay: 100 })
   consumer = undefined
 })