test(tools): add comprehensive unit tests for AskFollowupQuestionTool

- Add 36 unit tests covering execute(), handlePartial(), and error paths
- Fix undefined text handling: use safeText = text ?? "" to prevent literal 'undefined' in user_message output
- Add NativeToolCallParser integration tests for streaming ask_followup_question tool calls
- Address review feedback: fix undefined assertion and improve empty string comment clarity

Author: proyectoauraorg

src/core/tools/AskFollowupQuestionTool.ts

@@ -47,8 +47,9 @@ export class AskFollowupQuestionTool extends BaseTool<"ask_followup_question"> {
 
 			task.consecutiveMistakeCount = 0
 			const { text, images } = await task.ask("followup", JSON.stringify(follow_up_json), false)
-			await task.say("user_feedback", text ?? "", images)
-			pushToolResult(formatResponse.toolResult(`<user_message>\n${text}\n</user_message>`, images))
+			const safeText = text ?? ""
+			await task.say("user_feedback", safeText, images)
+			pushToolResult(formatResponse.toolResult(`<user_message>\n${safeText}\n</user_message>`, images))
 		} catch (error) {
 			await handleError("asking question", error as Error)
 		}