fix: disable thinking mode in QwenCodeHandler.completePrompt for prompt enhancement

qwen3-coder models are thinking models that return reasoning in a separate
reasoning_content field, which can leave message.content empty. The previous
fix only stripped <think> tags but did not address the root cause.

This change:
- Passes enable_thinking: false to the API to disable thinking mode for
  simple completions (prompt enhancement does not need reasoning)
- Falls back to reasoning_content if content is still empty
- Strips inline <think> blocks as an additional safety net

Closes #12102

src/api/providers/__tests__/qwen-code-complete-prompt.spec.ts

@@ -0,0 +1,215 @@
+// npx vitest run api/providers/__tests__/qwen-code-complete-prompt.spec.ts
+
+// Mock filesystem - must come before other imports
+vi.mock("node:fs", () => ({
+	promises: {
+		readFile: vi.fn(),
+		writeFile: vi.fn(),
+	},
+}))
+
+const mockCreate = vi.fn()
+vi.mock("openai", () => {
+	return {
+		__esModule: true,
+		default: vi.fn().mockImplementation(() => ({
+			apiKey: "test-key",
+			baseURL: "https://dashscope.aliyuncs.com/compatible-mode/v1",
+			chat: {
+				completions: {
+					create: mockCreate,
+				},
+			},
+		})),
+	}
+})
+
+import { promises as fs } from "node:fs"
+import { QwenCodeHandler } from "../qwen-code"
+import type { ApiHandlerOptions } from "../../../shared/api"
+
+describe("QwenCodeHandler completePrompt", () => {
+	let handler: QwenCodeHandler
+	let mockOptions: ApiHandlerOptions & { qwenCodeOauthPath?: string }
+
+	const validCredentials = {
+		access_token: "test-access-token",
+		refresh_token: "test-refresh-token",
+		token_type: "Bearer",
+		expiry_date: Date.now() + 3600000,
+		resource_url: "https://dashscope.aliyuncs.com/compatible-mode/v1",
+	}
+
+	beforeEach(() => {
+		vi.clearAllMocks()
+
+		mockOptions = {
+			apiModelId: "qwen3-coder-plus",
+			qwenCodeOauthPath: "/tmp/test-creds.json",
+		}
+
+		handler = new QwenCodeHandler(mockOptions)
+		;(fs.readFile as ReturnType<typeof vi.fn>).mockResolvedValue(JSON.stringify(validCredentials))
+	})
+
+	it("should return plain text content as-is", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "Here is your enhanced prompt with more details.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("Here is your enhanced prompt with more details.")
+	})
+
+	it("should pass enable_thinking: false in the request", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "Enhanced text",
+					},
+				},
+			],
+		})
+
+		await handler.completePrompt("Enhance this prompt")
+
+		expect(mockCreate).toHaveBeenCalledWith(
+			expect.objectContaining({
+				enable_thinking: false,
+			}),
+		)
+	})
+
+	it("should strip <think> blocks from response content", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content:
+							"<think>Let me analyze this prompt and think about how to enhance it...</think>Here is your enhanced prompt with more details.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("Here is your enhanced prompt with more details.")
+	})
+
+	it("should strip multiple <think> blocks from response content", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "<think>First thought...</think>Part one. <think>Second thought...</think>Part two.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("Part one. Part two.")
+	})
+
+	it("should fall back to reasoning_content when content is empty", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "",
+						reasoning_content: "The actual enhanced prompt text from reasoning.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("The actual enhanced prompt text from reasoning.")
+	})
+
+	it("should fall back to reasoning_content when content is null", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: null,
+						reasoning_content: "Enhanced prompt from reasoning_content field.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("Enhanced prompt from reasoning_content field.")
+	})
+
+	it("should return empty string when both content and reasoning_content are empty", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "",
+						reasoning_content: "",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("")
+	})
+
+	it("should handle response with only <think> blocks (content becomes empty after stripping)", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "<think>Only thinking, no actual content</think>",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("")
+	})
+
+	it("should handle multiline <think> blocks", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content:
+							"<think>\nStep 1: Analyze the prompt\nStep 2: Enhance it\nStep 3: Return result\n</think>\nHere is the enhanced prompt.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("Here is the enhanced prompt.")
+	})
+
+	it("should prefer content over reasoning_content when content is non-empty", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: "The actual content response.",
+						reasoning_content: "Some reasoning that should be ignored.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("The actual content response.")
+	})
+})

src/api/providers/qwen-code.ts

@@ -332,14 +332,33 @@ export class QwenCodeHandler extends BaseProvider implements SingleCompletionHan
 		const client = this.ensureClient()
 		const model = this.getModel()
 
-		const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming = {
+		// Disable thinking mode for simple completions (e.g. prompt enhancement).
+		// qwen3-coder models are thinking models that put reasoning in a separate
+		// `reasoning_content` field, which can leave `content` empty when thinking
+		// is enabled. Explicitly disabling it ensures content is populated.
+		const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming & {
+			enable_thinking?: boolean
+		} = {
 			model: model.id,
 			messages: [{ role: "user", content: prompt }],
 			max_completion_tokens: model.info.maxTokens,
+			enable_thinking: false,
 		}
 
-		const response = await this.callApiWithRetry(() => client.chat.completions.create(requestOptions))
+		const response = await this.callApiWithRetry(() => client.chat.completions.create(requestOptions as any))
 
-		return response.choices[0]?.message.content || ""
+		const message = response.choices[0]?.message
+		let content = message?.content || ""
+
+		// Fallback: if content is empty, check for reasoning_content (in case
+		// the API still returned thinking content despite enable_thinking: false).
+		if (!content && message && "reasoning_content" in message) {
+			content = (message as any).reasoning_content || ""
+		}
+
+		// Strip any inline <think>...</think> blocks that may be present.
+		content = content.replace(/<think>[\s\S]*?<\/think>/g, "").trim()
+
+		return content
 	}
 }