fix: terminal input reaches the shell in the order it was typed

internal/server/hub.go

@@ -45,6 +45,7 @@ type Session struct {
 	mu       sync.Mutex
 	inBuf    []proto.InFrame
 	inSignal chan struct{} // size-1; pulsed when inBuf gains data
+	inSeq    uint64        // number of the last browser message taken
 
 	out chan proto.OutMessage // agent -> panel
 
@@ -250,6 +251,19 @@ func (s *Session) close() { s.closeOnce.Do(func() { close(s.closed) }) }
 // Done returns a channel closed when the session ends.
 func (s *Session) Done() <-chan struct{} { return s.closed }
 
+// TakeSeq reports whether the browser message numbered seq is new, and takes
+// note of it. The browser sends them one at a time in rising order and sends
+// one again when it got no answer, so a number not above the last is a repeat.
+func (s *Session) TakeSeq(seq uint64) bool {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if seq <= s.inSeq {
+		return false
+	}
+	s.inSeq = seq
+	return true
+}
+
 // PushIn appends a downstream frame (panel -> agent) and wakes the agent poll.
 func (s *Session) PushIn(f proto.InFrame) {
 	s.mu.Lock()