feat(webrtc): add package skeleton and typed errors

.gitignore

@@ -7,6 +7,15 @@
 /test/**
 .vscode
 
+# Dragon Fork additions: source trees under /core/ and /test/ must be tracked.
+!/core/
+!/core/webrtc/
+!/core/webrtc/**
+!/test/
+!/test/publish.sh
+!/test/whep-client/
+!/test/whep-client/**
+
 *.ts
 *.ts.tmp
 *.m3u8

core/webrtc/doc.go

@@ -0,0 +1,11 @@
+// Package webrtc implements the Dragon Fork WebRTC egress module.
+//
+// It exposes a WHEP (WebRTC-HTTP Egress Protocol) HTTP endpoint and serves
+// live RTP produced by an FFmpeg process on a local UDP socket to one or
+// more WebRTC peer connections built with Pion.
+//
+// This package is additive: it does not modify existing datarhei ingest,
+// transcode, or non-WebRTC output code paths. The only contact with
+// existing code is a new URL scheme ("webrtc://") registered with the
+// output resolver (done in milestone M2, not here).
+package webrtc

core/webrtc/errors.go

@@ -0,0 +1,26 @@
+package webrtc
+
+import "errors"
+
+// Sentinel errors returned by package functions.
+var (
+	// ErrStreamNotFound indicates a WHEP subscribe referenced a stream_id
+	// that has no registered source. Maps to HTTP 404.
+	ErrStreamNotFound = errors.New("webrtc: stream not found")
+
+	// ErrPeerCapReached indicates max_peers_total has been exceeded.
+	// Maps to HTTP 503.
+	ErrPeerCapReached = errors.New("webrtc: peer capacity reached")
+
+	// ErrCodecMismatch indicates the viewer's SDP offer does not include
+	// a codec the source can serve (expected H.264 + Opus). Maps to HTTP 406.
+	ErrCodecMismatch = errors.New("webrtc: codec mismatch")
+
+	// ErrInvalidSDP indicates the request body was not a parseable SDP offer.
+	// Maps to HTTP 400.
+	ErrInvalidSDP = errors.New("webrtc: invalid SDP")
+
+	// ErrICETimeout indicates ICE gathering did not complete within the
+	// configured timeout. Maps to HTTP 500.
+	ErrICETimeout = errors.New("webrtc: ICE gathering timeout")
+)