feat(hooks): display hook system messages in UI (#24616)

packages/core/src/hooks/hookEventHandler.ts

@@ -458,6 +458,15 @@ export class HookEventHandler {
       );
 
       logHookCall(this.context.config, hookCallEvent);
+
+      // Emit structured system message event for UI display
+      if (result.output?.systemMessage && result.outputFormat === 'json') {
+        coreEvents.emitHookSystemMessage({
+          hookName,
+          eventName,
+          message: result.output.systemMessage,
+        });
+      }
     }
 
     // Log individual errors