Add reciprocal finish_reason validation and clarify session restore scope

- Override stop→tool_calls when tool calls are present (symmetric with
  the existing tool_calls→null guard)
- Expand comment explaining why session restore scopes to parent
  messages only

Author: trungutt

pkg/runtime/runtime.go

@@ -865,8 +865,11 @@ func (r *LocalRuntime) EmitStartupInfo(ctx context.Context, sess *session.Sessio
 
 		// Reconstruct LastMessage from the parent session's last assistant
 		// message so that FinishReason (and other per-message fields) are
-		// available on session restore.  We iterate sess.Messages directly
-		// (not GetAllMessages) to avoid picking up sub-agent messages.
+		// available on session restore.  We intentionally iterate
+		// sess.Messages (not GetAllMessages) so the result reflects the
+		// parent agent's state: this event carries the parent session_id,
+		// and sub-agents emit their own token_usage events with their own
+		// session_id during live streaming.
 		for i := len(sess.Messages) - 1; i >= 0; i-- {
 			item := &sess.Messages[i]
 			if !item.IsMessage() || item.Message.Message.Role != chat.MessageRoleAssistant {

pkg/runtime/streaming.go

@@ -219,9 +219,12 @@ func (r *LocalRuntime) handleStream(ctx context.Context, stream chat.MessageStre
 			finishReason = chat.FinishReasonNull
 		}
 	}
-	// Guard against a provider claiming tool_calls when no calls arrived.
-	if finishReason == chat.FinishReasonToolCalls && len(toolCalls) == 0 {
+	// Ensure finish reason agrees with the actual stream output.
+	switch {
+	case finishReason == chat.FinishReasonToolCalls && len(toolCalls) == 0:
 		finishReason = chat.FinishReasonNull
+	case finishReason == chat.FinishReasonStop && len(toolCalls) > 0:
+		finishReason = chat.FinishReasonToolCalls
 	}
 
 	return streamResult{