fix(ios-tests): wait for STOPPING before signalling node exit

[gmaclennan]

Summary

Fixes a race in testStopSendsShutdownMessageOverIPC that caused intermittent macOS Swift Package Test failures (e.g. on the #58 CI runs).

The race

The test dispatched service.stop(timeout: 2) to a background queue and then immediately called signalExit() on the main thread:

DispatchQueue.global().async {
    service.stop(timeout: 2)
    stopFinished.fulfill()
}
signalExit()

When the runner was loaded enough that the dispatched stop() hadn't started executing by the time signalExit() ran, the mock node thread's semaphore.wait() unblocked and the closure returned before stop() had set stopRequested = true. The state derivation rule Runtime exited unexpectedly → ERROR then fired (since the exit looked Unexpected), and when stop() finally ran it hit the guard:

guard state == .started || state == .starting else {
    log("Cannot stop: state is \(state.rawValue)")  // "ERROR"
    return
}

…and bailed without sending the shutdown frame. Result: service.state == .error and backend.receivedShutdown == false, both of which the test asserts against.

The fix

Register a STOPPING expectation alongside the existing STARTED one, and wait(for: [stoppingExpectation]) between dispatching stop() and calling signalExit(). The STOPPING transition is emitted inside stop() immediately after applyAndEmit { stopRequested = true }, so observing it guarantees stopRequested is true before the runtime exits — the exit is then classified as Requested, not Unexpected, and the state derives correctly to STOPPED.

Test plan

• swift test --filter NodeJSServiceTests/testStopSendsShutdownMessageOverIPC × 50 — all pass, durations cluster 53–63 ms
• swift test (full suite, 67 tests) — clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates the iOS Swift test suite to remove a race in NodeJSServiceTests/testStopSendsShutdownMessageOverIPC by ensuring stop() has begun (and the service has entered STOPPING) before the mock Node runtime is signalled to exit, preventing intermittent .error outcomes during CI.

Changes:

• Add a STOPPING expectation in testStopSendsShutdownMessageOverIPC.
• Replace the initial broad waitForExpectations with an explicit wait for STARTED, then wait for STOPPING before calling signalExit().

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