fix: sync protocol and discussion stability fixes

internal/mtprotoedge/inbound_rpc_test.go

@@ -3,11 +3,58 @@ package mtprotoedge
 import (
 	"context"
 	"errors"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
 )
 
+func TestStopInboundRPCTaskJoinsStartedDeadlineCallback(t *testing.T) {
+	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(-time.Second))
+	defer cancel()
+	started := make(chan struct{})
+	release := make(chan struct{})
+	var once sync.Once
+	ticket := &inboundRPCTicket{}
+	ticket.onTimeout = func() {
+		once.Do(func() {
+			close(started)
+			<-release
+		})
+	}
+	task := inboundRPC{
+		ctx:         ctx,
+		ticket:      ticket,
+		stopTimeout: func() bool { return false }, // runtime callback already scheduled
+	}
+	handoff := stopInboundRPCTask(task)
+	if handoff == nil {
+		t.Fatal("started deadline callback did not produce handoff")
+	}
+	go ticket.onTimeout()
+	select {
+	case <-started:
+	case <-time.After(time.Second):
+		t.Fatal("deadline callback did not start")
+	}
+	joined := make(chan struct{})
+	go func() {
+		handoff()
+		close(joined)
+	}()
+	select {
+	case <-joined:
+		t.Fatal("handoff returned before in-flight callback completed")
+	case <-time.After(20 * time.Millisecond):
+	}
+	close(release)
+	select {
+	case <-joined:
+	case <-time.After(time.Second):
+		t.Fatal("handoff did not join completed callback")
+	}
+}
+
 func newInboundTestConn(s *inboundRPCScheduler, maxInflight, queueSize int, timeout time.Duration) *Conn {
 	c := &Conn{metrics: NopMetrics{}}
 	c.startInboundRPCScheduler(s, maxInflight, queueSize, timeout)