test(byok/perplexity): add unit tests for curated list + integration header

Three cases:
- getAllModels returns the curated Agent API list with the correct base URL
  and asserts no sonar references remain.
- every model carries the X-Pplx-Integration header in merged capabilities.
- per-model requestHeaders cannot override the integration header.

Author: jliounis

src/extension/byok/vscode-node/test/perplexityProvider.spec.ts

@@ -0,0 +1,125 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { describe, expect, it, vi } from 'vitest';
+import { PerplexityLMProvider } from '../perplexityProvider';
+
+function createProvider(knownModels?: Record<string, any>) {
+	const fetch = vi.fn(async (url: string) => {
+		throw new Error(`Unexpected fetch in test: ${url}`);
+	});
+
+	const logService = {
+		_serviceBrand: undefined,
+		trace: vi.fn(),
+		debug: vi.fn(),
+		info: vi.fn(),
+		warn: vi.fn(),
+		error: vi.fn(),
+		show: vi.fn(),
+		createSubLogger: vi.fn(),
+		withExtraTarget: vi.fn(),
+	};
+	logService.createSubLogger.mockReturnValue(logService);
+	logService.withExtraTarget.mockReturnValue(logService);
+
+	const storage = {
+		getAPIKey: vi.fn().mockResolvedValue(undefined),
+		storeAPIKey: vi.fn().mockResolvedValue(undefined),
+		deleteAPIKey: vi.fn().mockResolvedValue(undefined),
+		getStoredModelConfigs: vi.fn().mockResolvedValue({}),
+		saveModelConfig: vi.fn().mockResolvedValue(undefined),
+		removeModelConfig: vi.fn().mockResolvedValue(undefined),
+	};
+
+	const provider = new PerplexityLMProvider(
+		knownModels as any,
+		storage as any,
+		{ fetch } as any,
+		logService as any,
+		{ createInstance: vi.fn().mockReturnValue({}) } as any,
+		{
+			isConfigured: vi.fn().mockReturnValue(false),
+			getConfig: vi.fn(),
+			setConfig: vi.fn(),
+		} as any,
+		{} as any
+	);
+
+	return { provider, fetch, storage, logService };
+}
+
+describe('PerplexityLMProvider', () => {
+	it('getAllModels returns the curated Agent API model list', async () => {
+		const { provider, fetch } = createProvider();
+
+		const models = await (provider as any).getAllModels(true, 'test-api-key', undefined);
+
+		expect(models.length).toBe(5);
+
+		const expectedIds = [
+			'openai/gpt-5.4',
+			'openai/gpt-5.2',
+			'anthropic/claude-sonnet-4-6',
+			'anthropic/claude-opus-4-7',
+			'google/gemini-3-1-pro',
+		];
+		const ids = models.map((m: any) => m.id);
+		expect(ids.sort()).toEqual(expectedIds.sort());
+
+		// No sonar references at all in the curated list.
+		expect(models.some((m: any) => m.id.includes('sonar'))).toBe(false);
+		expect(models.some((m: any) => (m.name ?? '').toLowerCase().includes('sonar'))).toBe(false);
+
+		// Each model points at the Agent API base URL.
+		for (const model of models) {
+			expect(model.url).toBe('https://api.perplexity.ai/v1');
+		}
+
+		// /models endpoint must never be queried — getAllModels is overridden.
+		expect(fetch).not.toHaveBeenCalled();
+	});
+
+	it('every model includes X-Pplx-Integration header in merged capabilities', async () => {
+		const { provider } = createProvider();
+
+		const knownModels = (provider as any)._knownModels as Record<string, { requestHeaders?: Record<string, string> }>;
+		expect(knownModels).toBeDefined();
+		const ids = Object.keys(knownModels);
+		expect(ids.length).toBe(5);
+
+		for (const id of ids) {
+			const headers = knownModels[id].requestHeaders;
+			expect(headers).toBeDefined();
+			expect(headers!['X-Pplx-Integration']).toMatch(/^vscode-copilot\//);
+		}
+	});
+
+	it('integration header is not overridden by per-model requestHeaders', () => {
+		const { provider } = createProvider({
+			'openai/gpt-5.4': {
+				name: 'GPT-5.4 (custom)',
+				toolCalling: true,
+				vision: true,
+				maxInputTokens: 200000,
+				maxOutputTokens: 16000,
+				requestHeaders: {
+					'X-Pplx-Integration': 'malicious-override',
+					'X-Custom-Header': 'kept',
+				},
+			},
+		});
+
+		const knownModels = (provider as any)._knownModels as Record<string, { requestHeaders?: Record<string, string> }>;
+		const headers = knownModels['openai/gpt-5.4'].requestHeaders!;
+
+		// The provider's integration header always wins.
+		expect(headers['X-Pplx-Integration']).toMatch(/^vscode-copilot\//);
+		expect(headers['X-Pplx-Integration']).not.toBe('malicious-override');
+
+		// Other custom headers should be preserved.
+		expect(headers['X-Custom-Header']).toBe('kept');
+	});
+});