fix(video): make pause/resume race-free by routing through the new dispatcher

Replaces the inline switch in onRPCMessage with a pair of regular
RPCHandler entries flagged TakesSession + Synchronous. The dispatcher
runs them on the per-session rpcQueue pump goroutine — which is the
single sequential consumer of the queue — so a rapid pause→resume pair
can no longer be reordered by the Go scheduler. Previously each RPC
was dispatched via "go onRPCMessage(...)", letting the scheduler
interleave the two helpers so a release could land after the matching
acquire and leave the encoder stopped while the tab was visible.

Reported by Cursor Bugbot:
#1455 (comment)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: mcuelenaere

jsonrpc.go

@@ -126,22 +126,6 @@ func onRPCMessage(message webrtc.DataChannelMessage, session *Session) {
 		return
 	}
 
-	// pauseVideo / resumeVideo are session-bound notifications: they
-	// toggle this session's slot in the video stream refcount (see
-	// video.go). Handled inline because the generic dispatcher doesn't
-	// pass *Session, and acting on currentSession instead of the
-	// receiving session would let a stale data channel mis-target the
-	// active one during the 1s handover overlap. Both helpers are
-	// idempotent so rapid pause/resume bursts are safe.
-	switch request.Method {
-	case "pauseVideo":
-		releaseVideoStream(session.videoConsumerKey())
-		return
-	case "resumeVideo":
-		acquireVideoStream(session.videoConsumerKey())
-		return
-	}
-
 	handler, ok := rpcHandlers[request.Method]
 	if !ok {
 		errorResponse := JSONRPCResponse{
@@ -1381,6 +1365,8 @@ var rpcHandlers = map[string]RPCHandler{
 	"wheelReport":                {Func: rpcWheelReport, Params: []string{"wheelY", "wheelX"}},
 	"wakeHost":                   {Func: rpcWakeHost},
 	"getVideoState":              {Func: rpcGetVideoState},
+	"pauseVideo":                 {Func: rpcPauseVideo, TakesSession: true, Synchronous: true},
+	"resumeVideo":                {Func: rpcResumeVideo, TakesSession: true, Synchronous: true},
 	"getUSBState":                {Func: rpcGetUSBState},
 	"unmountImage":               {Func: rpcUnmountImage},
 	"rpcMountBuiltInImage":       {Func: rpcMountBuiltInImage, Params: []string{"filename"}},

video.go

@@ -157,6 +157,22 @@ func updateHostDisplayAdvertisement(reason string, force bool) error {
 	return setHostDisplayAdvertisedLocked(shouldAdvertiseHostDisplayLocked(), reason, force)
 }
 
+// rpcPauseVideo releases this session's slot in the video stream
+// refcount. Registered with TakesSession + Synchronous so it acts on
+// the receiving session and can't be reordered relative to a
+// resumeVideo from the same source.
+func rpcPauseVideo(s *Session) error {
+	releaseVideoStream(s.videoConsumerKey())
+	return nil
+}
+
+// rpcResumeVideo re-acquires this session's slot. See rpcPauseVideo for
+// the dispatcher flags this relies on.
+func rpcResumeVideo(s *Session) error {
+	acquireVideoStream(s.videoConsumerKey())
+	return nil
+}
+
 type rpcVideoSleepModeResponse struct {
 	Supported bool `json:"supported"`
 	Enabled   bool `json:"enabled"`