Always proxy WHIP ingresses that bypass transcoding

[biglittlebigben]

WHIP requests with transcoding disabled were handled one of two ways depending on the whip_proxy_enabled config: in-process by the native whipHandler, publishing to the room over the LiveKit SDK, or forwarded to the SFU by the proxy handler. This drops the in-process variant and always proxies, so the native handler is now used only when transcoding.

Removed

• SDKMediaSink and SDKWhipTrackHandler, and the runSession / addTrack branches that drove them.
• The whipHandler IngressHandler RPC implementations. It only registered them when createStream handed it a bus, which happened solely in the bypass branch — bypass sessions are now served by proxyWhipHandler and transcoded ones by the handler process, so whipHandler no longer registers RPCs at all and can no longer fail to construct.
• The whip_proxy_enabled config field and the getWhipProxyEnabled callback to WHIPServer.Start.
• The interceptor and simulcast branches that only applied without transcoding.

Quality plumbing

With the native handler restricted to transcoding, it rejects any offer carrying simulcast layers, so a track's quality could only ever be HIGH. trackHandlers is keyed by types.StreamKind directly and RelayWhipTrackHandler loses its quality field.

This changes the video media stats path from input.video.HIGH to input.video, matching what the RTMP server and the media pipeline already register. Worth a look from anyone with dashboards or alerts keyed on the old path.

Orphaned by the above

replaceICEDetails, utils.ReplaceRTCPPacketSSRC and its test, and the lksdk_output PacketSink plumbing, LocalTrack.WriteRTP and LKSDKOutput.WriteRTCP.

Verification

Every removed symbol was traced to its callers on main; each one's only callers were inside the deleted bypass path. The four RPC methods dropped from the WHIPHandler interface were never invoked through it — the server reaches them over psrpc via s.rpcClient. Config parsing is non-strict yaml.Unmarshal, so deployments still carrying whip_proxy_enabled load fine with the key ignored.

go build ./..., go vet -tags integration ./... and go test ./pkg/... pass.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.