fix: strip thinking blocks from qwen-code completePrompt responses

qwen3-coder models include <think>...</think> blocks in their responses.
The completePrompt() method (used for prompt enhancement) was returning
these blocks as-is, causing the enhanced prompt to either be empty
(triggering "Failed to enhance prompt" toast) or contain raw thinking
markup.

This strips <think> blocks from the response content before returning,
consistent with how createMessage() already handles them for streaming.

Closes #12102

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

@@ -0,0 +1,146 @@
+// 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 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 handle multiline <think> blocks", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content:
+							"<think>\nLet me think about this.\nI need to consider multiple things.\n</think>\nThe enhanced prompt.",
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("The enhanced prompt.")
+	})
+
+	it("should return empty string when content is only a think block", 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 return empty string when message content is null", async () => {
+		mockCreate.mockResolvedValueOnce({
+			choices: [
+				{
+					message: {
+						content: null,
+					},
+				},
+			],
+		})
+
+		const result = await handler.completePrompt("Enhance this prompt")
+		expect(result).toBe("")
+	})
+})

src/api/providers/qwen-code.ts

@@ -340,6 +340,9 @@ export class QwenCodeHandler extends BaseProvider implements SingleCompletionHan
 
 		const response = await this.callApiWithRetry(() => client.chat.completions.create(requestOptions))
 
-		return response.choices[0]?.message.content || ""
+		const content = response.choices[0]?.message.content || ""
+
+		// Strip <think>...</think> blocks that qwen3-coder thinking models include
+		return content.replace(/<think>[\s\S]*?<\/think>/g, "").trim()
 	}
 }