feat: WebRTC transport — peer-to-peer data channels with auto-fallback
Relay:
- /signal/{channel} path for SDP/ICE exchange via WebSocket
- handle_signaling broadcasts text messages between signaling peers
- signaling_tx broadcast channel in ChannelState
- 46 ds-stream tests (+2 signaling path tests)
JS Runtime:
- _initWebRTC(signalingUrl, streamUrl, mode) with RTCPeerConnection
- Unordered DataChannel (ordered:false, maxRetransmits:0) for low latency
- Auto-fallback: WebSocket starts immediately, WebRTC upgrades in ≤5s
- Data channel override of _streamSend for transparent binary protocol
Parser/AST:
- StreamTransport enum (WebSocket, WebRTC)
- transport field in StreamDecl
- Parses: stream x on url { mode: signal, transport: webrtc }
Codegen:
- WebRTC: emits DS._initWebRTC(sigUrl, streamUrl, mode)
- WebSocket: emits DS._initStream(url, mode) (unchanged)
97 tests, 0 failures
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