From 77ed60a1731e3317474e45b069e743d646e30980 Mon Sep 17 00:00:00 2001
From: rossdonald <49425722+rossdonald@users.noreply.github.com>
Date: Tue, 17 Feb 2026 04:14:37 +1100
Subject: [PATCH] fix: add follow_up param validation in
 AskFollowupQuestionTool (#11484)

Added strict validation for the `follow_up` parameter to
check for presence and type (Array). Added test cases
covering missing, null, and invalid type scenarios.
Refactored parameter error handling into a helper method to reduce
duplication.
---
 src/core/tools/AskFollowupQuestionTool.ts     | 17 +++-
 .../__tests__/askFollowupQuestionTool.spec.ts | 85 +++++++++++++++++++
 2 files changed, 98 insertions(+), 4 deletions(-)

diff --git a/src/core/tools/AskFollowupQuestionTool.ts b/src/core/tools/AskFollowupQuestionTool.ts
index 010a6240f1..22cdbcf5de 100644
--- a/src/core/tools/AskFollowupQuestionTool.ts
+++ b/src/core/tools/AskFollowupQuestionTool.ts
@@ -21,12 +21,21 @@ export class AskFollowupQuestionTool extends BaseTool<"ask_followup_question"> {
 		const { question, follow_up } = params
 		const { handleError, pushToolResult } = callbacks
 
+		const recordMissingParamError = async (paramName: string): Promise<void> => {
+			task.consecutiveMistakeCount++
+			task.recordToolError("ask_followup_question")
+			task.didToolFailInCurrentTurn = true
+			pushToolResult(await task.sayAndCreateMissingParamError("ask_followup_question", paramName))
+		}
+
 		try {
 			if (!question) {
-				task.consecutiveMistakeCount++
-				task.recordToolError("ask_followup_question")
-				task.didToolFailInCurrentTurn = true
-				pushToolResult(await task.sayAndCreateMissingParamError("ask_followup_question", "question"))
+				await recordMissingParamError("question")
+				return
+			}
+
+			if (!follow_up || !Array.isArray(follow_up)) {
+				await recordMissingParamError("follow_up")
 				return
 			}
 
diff --git a/src/core/tools/__tests__/askFollowupQuestionTool.spec.ts b/src/core/tools/__tests__/askFollowupQuestionTool.spec.ts
index e13f639ba0..63bfad8a3d 100644
--- a/src/core/tools/__tests__/askFollowupQuestionTool.spec.ts
+++ b/src/core/tools/__tests__/askFollowupQuestionTool.spec.ts
@@ -13,7 +13,9 @@ describe("askFollowupQuestionTool", () => {
 		mockCline = {
 			ask: vi.fn().mockResolvedValue({ text: "Test response" }),
 			say: vi.fn().mockResolvedValue(undefined),
+			sayAndCreateMissingParamError: vi.fn().mockResolvedValue("Missing parameter error"),
 			consecutiveMistakeCount: 0,
+			recordToolError: vi.fn(),
 		}
 
 		mockPushToolResult = vi.fn((result) => {
@@ -109,6 +111,89 @@ describe("askFollowupQuestionTool", () => {
 		)
 	})
 
+	describe("parameter validation", () => {
+		it("should handle missing follow_up parameter", async () => {
+			const block: ToolUse = {
+				type: "tool_use",
+				name: "ask_followup_question",
+				params: {
+					question: "What would you like to do?",
+				},
+				nativeArgs: {
+					question: "What would you like to do?",
+					follow_up: undefined as any,
+				},
+				partial: false,
+			}
+
+			await askFollowupQuestionTool.handle(mockCline, block as ToolUse<"ask_followup_question">, {
+				askApproval: vi.fn(),
+				handleError: vi.fn(),
+				pushToolResult: mockPushToolResult,
+			})
+
+			expect(mockCline.sayAndCreateMissingParamError).toHaveBeenCalledWith("ask_followup_question", "follow_up")
+			expect(mockCline.recordToolError).toHaveBeenCalledWith("ask_followup_question")
+			expect(mockCline.didToolFailInCurrentTurn).toBe(true)
+			expect(mockCline.consecutiveMistakeCount).toBe(1)
+			expect(mockCline.ask).not.toHaveBeenCalled()
+		})
+
+		it("should handle null follow_up parameter", async () => {
+			const block: ToolUse = {
+				type: "tool_use",
+				name: "ask_followup_question",
+				params: {
+					question: "What would you like to do?",
+				},
+				nativeArgs: {
+					question: "What would you like to do?",
+					follow_up: null as any,
+				},
+				partial: false,
+			}
+
+			await askFollowupQuestionTool.handle(mockCline, block as ToolUse<"ask_followup_question">, {
+				askApproval: vi.fn(),
+				handleError: vi.fn(),
+				pushToolResult: mockPushToolResult,
+			})
+
+			expect(mockCline.sayAndCreateMissingParamError).toHaveBeenCalledWith("ask_followup_question", "follow_up")
+			expect(mockCline.recordToolError).toHaveBeenCalledWith("ask_followup_question")
+			expect(mockCline.didToolFailInCurrentTurn).toBe(true)
+			expect(mockCline.consecutiveMistakeCount).toBe(1)
+			expect(mockCline.ask).not.toHaveBeenCalled()
+		})
+
+		it("should handle non-array follow_up parameter", async () => {
+			const block: ToolUse = {
+				type: "tool_use",
+				name: "ask_followup_question",
+				params: {
+					question: "What would you like to do?",
+				},
+				nativeArgs: {
+					question: "What would you like to do?",
+					follow_up: "not an array" as any,
+				} as any,
+				partial: false,
+			}
+
+			await askFollowupQuestionTool.handle(mockCline, block as ToolUse<"ask_followup_question">, {
+				askApproval: vi.fn(),
+				handleError: vi.fn(),
+				pushToolResult: mockPushToolResult,
+			})
+
+			expect(mockCline.sayAndCreateMissingParamError).toHaveBeenCalledWith("ask_followup_question", "follow_up")
+			expect(mockCline.recordToolError).toHaveBeenCalledWith("ask_followup_question")
+			expect(mockCline.didToolFailInCurrentTurn).toBe(true)
+			expect(mockCline.consecutiveMistakeCount).toBe(1)
+			expect(mockCline.ask).not.toHaveBeenCalled()
+		})
+	})
+
 	describe("handlePartial with native protocol", () => {
 		it("should only send question during partial streaming to avoid raw JSON display", async () => {
 			const block: ToolUse<"ask_followup_question"> = {