First milestone of the injection render-hook audio path (see
docs/audio-render-hook-plan.md) that fixes the local audio echo without a
virtual device.
- common/include/coop/audio_ring.hpp: new lock-free SPSC shared-memory ring
for PCM, separate from the input/status SharedBlock. Free-running 64-bit
positions (release/acquire), format handshake, host-owned capture_enabled
gate, drop-whole-packet overrun policy.
- common/include/coop/protocol.hpp: add AudioStreamInfo + audio_streams_seen /
audio_streams[] to the always-present HookStatus for the render-stream-count
debug view; bump kProtocolVersion 3->4 (new members appended).
- tests/audio_ring_test.cpp: in-process unit test (push/pop integrity,
wrap-around, format handshake, overrun/drop). No hook or audio device.
- docs/audio-render-hook-plan.md: the green-lit design this implements.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
