feat: US-008 - Inject callback into async tools in AgentLoop

- Update ToolRegistry.ExecuteWithContext to accept asyncCallback parameter
- Check if tool implements AsyncTool and set callback if provided
- Define asyncCallback in AgentLoop.runLLMIteration
- Callback uses bus.PublishOutbound to send async results to user
- Update Execute method to pass nil for backward compatibility
- Add debug logging for async callback injection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/tools/registry.go

@@ -34,10 +34,13 @@ func (r *ToolRegistry) Get(name string) (Tool, bool) {
 }
 
 func (r *ToolRegistry) Execute(ctx context.Context, name string, args map[string]interface{}) *ToolResult {
-	return r.ExecuteWithContext(ctx, name, args, "", "")
+	return r.ExecuteWithContext(ctx, name, args, "", "", nil)
 }
 
-func (r *ToolRegistry) ExecuteWithContext(ctx context.Context, name string, args map[string]interface{}, channel, chatID string) *ToolResult {
+// ExecuteWithContext executes a tool with channel/chatID context and optional async callback.
+// If the tool implements AsyncTool and a non-nil callback is provided,
+// the callback will be set on the tool before execution.
+func (r *ToolRegistry) ExecuteWithContext(ctx context.Context, name string, args map[string]interface{}, channel, chatID string, asyncCallback AsyncCallback) *ToolResult {
 	logger.InfoCF("tool", "Tool execution started",
 		map[string]interface{}{
 			"tool": name,
@@ -58,6 +61,15 @@ func (r *ToolRegistry) ExecuteWithContext(ctx context.Context, name string, args
 		contextualTool.SetContext(channel, chatID)
 	}
 
+	// If tool implements AsyncTool and callback is provided, set callback
+	if asyncTool, ok := tool.(AsyncTool); ok && asyncCallback != nil {
+		asyncTool.SetCallback(asyncCallback)
+		logger.DebugCF("tool", "Async callback injected",
+			map[string]interface{}{
+				"tool": name,
+			})
+	}
+
 	start := time.Now()
 	result := tool.Execute(ctx, args)
 	duration := time.Since(start)