fix(tui): propagate error messages when subagent tasks crash

cortex-tui/src/runner/event_loop.rs

@@ -1422,6 +1422,10 @@ impl EventLoop {
                 // Update toast notifications (for auto-dismiss with fade)
                 self.app_state.toasts.tick();
 
+                // Check for crashed subagent tasks (panics, cancellations)
+                // This ensures the main agent always receives a response even if a subagent crashes
+                self.check_crashed_tasks().await;
+
                 // Render frame (respecting frame time to avoid over-rendering)
                 if self.last_render.elapsed() >= self.min_frame_time {
                     self.render(terminal)?;
@@ -3466,6 +3470,66 @@ impl EventLoop {
         }
     }
 
+    /// Checks for crashed background tool tasks (panics or cancelled).
+    ///
+    /// This method is called periodically to detect subagent tasks that have
+    /// terminated unexpectedly without sending a completion or failure event.
+    /// When a crashed task is detected, it sends a ToolEvent::Failed to ensure
+    /// the main agent always receives a response.
+    async fn check_crashed_tasks(&mut self) {
+        // Collect crashed task IDs and their errors
+        let mut crashed_tasks: Vec<(String, String)> = Vec::new();
+
+        // Check all running tool tasks
+        for (id, handle) in self.running_tool_tasks.iter() {
+            if handle.is_finished() {
+                // Task finished - check if it panicked by trying to get the result
+                // Note: We can't actually await the handle here since we don't own it,
+                // but is_finished() alone tells us the task ended unexpectedly
+                // (if it ended normally, it would have sent Completed/Failed events
+                // which would have removed it from running_tool_tasks)
+                crashed_tasks.push((
+                    id.clone(),
+                    "Subagent task terminated unexpectedly (possible panic or cancellation)"
+                        .to_string(),
+                ));
+            }
+        }
+
+        // Process crashed tasks
+        for (id, error) in crashed_tasks {
+            tracing::error!("Detected crashed subagent task: {} - {}", id, error);
+
+            // Remove from running tasks
+            if let Some(handle) = self.running_tool_tasks.remove(&id) {
+                // Try to get the panic message if possible
+                let error_msg = match handle.await {
+                    Ok(()) => error, // Task completed but didn't send event - shouldn't happen
+                    Err(join_error) => {
+                        if join_error.is_panic() {
+                            format!("Subagent panicked: {:?}", join_error.into_panic())
+                        } else if join_error.is_cancelled() {
+                            "Subagent task was cancelled".to_string()
+                        } else {
+                            format!("Subagent task failed: {}", join_error)
+                        }
+                    }
+                };
+
+                // Send failure event through the tool event channel
+                let _ = self
+                    .tool_event_tx
+                    .send(ToolEvent::Failed {
+                        id: id.clone(),
+                        name: "Task".to_string(),
+                        error: error_msg,
+                        duration: std::time::Duration::from_secs(0),
+                    })
+                    .await;
+            }
+        }
+    }
+
     // ========================================================================
     // SUBAGENT EVENT HANDLING
     // ========================================================================