fix: add close(errCh) comments and sendingMessage race fix

Add comments explaining why close(msg.errCh) is called at both sites.

Add sendingMessage flag to prevent statusLocked() from returning
'stable' while the send loop is processing a dequeued message
outside the lock.

Author: johnstcn

lib/screentracker/pty_conversation.go

@@ -99,6 +99,10 @@ type PTYConversation struct {
 	// layer holds s.mu, and Send blocks until the message is processed),
 	// so ordering is preserved.
 	outboundQueue chan outboundMessage
+	// sendingMessage is true while the send loop is processing a message.
+	// Set under lock in the snapshot loop when signaling, cleared under
+	// lock in the send loop after sendMessage returns.
+	sendingMessage bool
 	// stableSignal is used by the snapshot loop to signal the send loop
 	// when the agent is stable and there are items in the outbound queue.
 	stableSignal chan struct{}
@@ -162,6 +166,7 @@ func (c *PTYConversation) Start(ctx context.Context) {
 		if c.initialPromptReady && len(c.outboundQueue) > 0 && c.isScreenStableLocked() {
 			select {
 			case c.stableSignal <- struct{}{}:
+				c.sendingMessage = true
 			default:
 				// Signal already pending
 			}
@@ -181,6 +186,8 @@ func (c *PTYConversation) Start(ctx context.Context) {
 				case msg := <-c.outboundQueue:
 					if msg.errCh != nil {
 						msg.errCh <- ctx.Err()
+						// Close so the Send() caller's <-errCh never blocks
+						// if it has already consumed the error value.
 						close(msg.errCh)
 					}
 				default:
@@ -198,8 +205,13 @@ func (c *PTYConversation) Start(ctx context.Context) {
 					return
 				case msg := <-c.outboundQueue:
 					err := c.sendMessage(ctx, msg.parts...)
+					c.lock.Lock()
+					c.sendingMessage = false
+					c.lock.Unlock()
 					if msg.errCh != nil {
 						msg.errCh <- err
+						// Close so the Send() caller's <-errCh never blocks
+						// if it has already consumed the error value.
 						close(msg.errCh)
 					}
 				default:
@@ -448,7 +460,7 @@ func (c *PTYConversation) statusLocked() ConversationStatus {
 
 	// Handle initial prompt readiness: report "changing" until the queue is drained
 	// to avoid the status flipping "changing" -> "stable" -> "changing"
-	if len(c.outboundQueue) > 0 {
+	if len(c.outboundQueue) > 0 || c.sendingMessage {
 		return ConversationStatusChanging
 	}