fix(subagent): add logging for silent errors in subagent communication (#310)

- Replace silent 'let _ =' patterns with proper error logging in spawn_subagent
- Log errors when ToolEvent channel send fails (Started, Failed, Completed, TodoUpdated)
- Add warning when stream ends without Done event
- Log status update failures in AgentThread.set_status()

This helps diagnose issues where subagents stop without returning results.

Co-authored-by: Droid <droid@factory.ai>

Author: echobt

cortex-agents/src/control.rs

@@ -5,9 +5,9 @@
 
 use crate::AgentInfo;
 use std::collections::HashMap;
-use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
-use tokio::sync::{watch, RwLock};
+use std::sync::atomic::{AtomicUsize, Ordering};
+use tokio::sync::{RwLock, watch};
 use uuid::Uuid;
 
 /// Unique identifier for an agent thread.
@@ -39,9 +39,10 @@ impl std::fmt::Display for AgentThreadId {
 }
 
 /// Status of an agent in the control system.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub enum AgentThreadStatus {
     /// Agent is being initialized.
+    #[default]
     PendingInit,
     /// Agent is running.
     Running,
@@ -68,12 +69,6 @@ impl AgentThreadStatus {
     }
 }
 
-impl Default for AgentThreadStatus {
-    fn default() -> Self {
-        AgentThreadStatus::PendingInit
-    }
-}
-
 /// An agent thread managed by the control system.
 pub struct AgentThread {
     /// Thread ID.
@@ -119,7 +114,13 @@ impl AgentThread {
 
     /// Update status.
     pub fn set_status(&self, status: AgentThreadStatus) {
-        let _ = self.status_tx.send(status);
+        if self.status_tx.send(status.clone()).is_err() {
+            tracing::warn!(
+                "Failed to send status update {:?} for agent {} - all receivers dropped",
+                status,
+                self.id
+            );
+        }
     }
 
     /// Subscribe to status updates.