Boot → beep → user speaks → server VAD ends turn → assistant audio
plays back → exit 0. No wakeword, no loop, no state machine.
Splits Test 4 into 4a (this spec) and 4b (wakeword + loop + 16↔24 kHz
coexistence, future). 4a debugs the OpenAI Realtime surface — auth, WS
handshake, session.update payload, server VAD, base64 audio, streaming-
length output-stream cleanup — in isolation from 4b's harder concurrency.
