🤖 fix: send queued messages on tool-call-end (#665)

Queued messages are now sent as soon as a tool completes execution,
rather than waiting for the entire stream to finish.

## Problem

Previously, queued messages were only sent on `stream-end`. In
tool-using flows, this meant users had to wait for:
1. Tool execution to complete
2. LLM to process the tool result
3. LLM to finish streaming its response

This created unnecessary latency when queueing messages during tool
execution.

## Solution

Extracted a shared `sendQueuedMessages()` method called from both:
- `tool-call-end`: Sends queued messages immediately when tool completes
- `stream-end`: Continues to handle non-tool streams

The first handler to fire clears the queue, so no duplicate sends occur.
Non-tool streams continue to work exactly as before.

## Changes

- Added `sendQueuedMessages()` private method
- Updated `tool-call-end` handler to auto-send
- Refactored `stream-end` handler to use shared method

Net: +18 lines

_Generated with `mux`_

Author: ethanndickson

src/node/services/agentSession.ts

@@ -408,20 +408,18 @@ export class AgentSession {
     forward("stream-delta", (payload) => this.emitChatEvent(payload));
     forward("tool-call-start", (payload) => this.emitChatEvent(payload));
     forward("tool-call-delta", (payload) => this.emitChatEvent(payload));
-    forward("tool-call-end", (payload) => this.emitChatEvent(payload));
+    forward("tool-call-end", (payload) => {
+      this.emitChatEvent(payload);
+      // Tool call completed: auto-send queued messages
+      this.sendQueuedMessages();
+    });
     forward("reasoning-delta", (payload) => this.emitChatEvent(payload));
     forward("reasoning-end", (payload) => this.emitChatEvent(payload));
 
     forward("stream-end", (payload) => {
       this.emitChatEvent(payload);
       // Stream end: auto-send queued messages
-      if (!this.messageQueue.isEmpty()) {
-        const { message, options } = this.messageQueue.produceMessage();
-        this.messageQueue.clear();
-        this.emitQueuedMessageChanged();
-
-        void this.sendMessage(message, options);
-      }
+      this.sendQueuedMessages();
     });
 
     forward("stream-abort", (payload) => {
@@ -529,6 +527,20 @@ export class AgentSession {
     });
   }
 
+  /**
+   * Send queued messages if any exist.
+   * Called when tool execution completes or stream ends.
+   */
+  private sendQueuedMessages(): void {
+    if (!this.messageQueue.isEmpty()) {
+      const { message, options } = this.messageQueue.produceMessage();
+      this.messageQueue.clear();
+      this.emitQueuedMessageChanged();
+
+      void this.sendMessage(message, options);
+    }
+  }
+
   private assertNotDisposed(operation: string): void {
     assert(!this.disposed, `AgentSession.${operation} called after dispose`);
   }