fix(opencode): avoid shell cancel race (#30641)

packages/opencode/test/session/prompt.test.ts

@@ -320,10 +320,9 @@ const useServerConfig = Effect.fn("test.useServerConfig")(function* (config: (ur
   return { dir, llm }
 })
 
-// Wait for a session's runner to enter a busy state. SessionStatus is flipped to
-// "busy" inside Runner.startShell's modifyEffect at the same moment the runner
-// is registered, so this is a deterministic readiness signal — cancel can't
-// no-op once we observe it.
+// Wait for a session's runner to enter a busy state. SessionStatus is flipped
+// inside Runner.startShell's serialized transition, so cancel can't no-op once
+// we observe it.
 const waitForBusy = (sessionID: SessionID, duration: Duration.Input = "2 seconds") =>
   pollWithTimeout(
     Effect.gen(function* () {