feat: add OpenRouter provider to golden harness, close Phase 0 gate

- provider-agnostic llm-client (grok + openrouter) with page-slug context
- live golden run scored and passing via x-ai/grok-4.6
- ADR 0010; spike docs flipped to done

e2e/golden/src/llm-client.ts

@@ -1,21 +1,47 @@
 import type { GrokResponse } from './types.ts';
 
-const url = 'https://api.x.ai/v1/chat/completions';
+export type LlmProvider = 'grok' | 'openrouter';
 
-export async function callGrok(input: {
+export type LlmConfig = {
+  baseUrl: string;
+  model: string;
+};
+
+const PROVIDERS: Record<LlmProvider, LlmConfig> = {
+  grok: { baseUrl: 'https://api.x.ai/v1', model: 'grok-3' },
+  openrouter: { baseUrl: 'https://openrouter.ai/api/v1', model: 'x-ai/grok-4.6' },
+};
+
+export function resolveProvider(provider: LlmProvider, model?: string): LlmConfig {
+  const config = PROVIDERS[provider];
+  return { baseUrl: config.baseUrl, model: model ?? config.model };
+}
+
+export async function callLlm(input: {
+  provider: LlmProvider;
   apiKey: string;
+  model?: string;
   prompt: string;
   siteId: string;
   builder: string;
+  pages?: string[];
 }): Promise<GrokResponse> {
-  const response = await fetch(url, {
+  const { baseUrl, model } = resolveProvider(input.provider, input.model);
+
+  const headers: Record<string, string> = {
+    Authorization: `Bearer ${input.apiKey}`,
+    'Content-Type': 'application/json',
+  };
+  if (input.provider === 'openrouter') {
+    headers['HTTP-Referer'] = 'https://wursor.dev';
+    headers['X-Title'] = 'Wursor golden harness';
+  }
+
+  const response = await fetch(`${baseUrl}/chat/completions`, {
     method: 'POST',
-    headers: {
-      Authorization: `Bearer ${input.apiKey}`,
-      'Content-Type': 'application/json',
-    },
+    headers,
     body: JSON.stringify({
-      model: 'grok-3',
+      model,
       messages: [
         {
           role: 'system',
@@ -24,7 +50,7 @@ export async function callGrok(input: {
         },
         {
           role: 'user',
-          content: `site=${input.siteId} builder=${input.builder}\n${input.prompt}`,
+          content: `site=${input.siteId} builder=${input.builder}${input.pages ? ` pages=${input.pages.join(',')}` : ''}\n${input.prompt}`,
         },
       ],
       tools: [
@@ -71,7 +97,7 @@ export async function callGrok(input: {
   });
 
   if (!response.ok) {
-    throw new Error(`Grok HTTP ${response.status}`);
+    throw new Error(`LLM HTTP ${response.status}`);
   }
   return (await response.json()) as GrokResponse;
 }

e2e/golden/src/run-golden.ts

@@ -3,15 +3,19 @@ import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { detectBuilder } from './builder-detect.ts';
 import { asGrokResponse, expectedCalls } from './expected-calls.ts';
-import { callGrok } from './grok-client.ts';
+import { callLlm, type LlmProvider } from './llm-client.ts';
 import { loadPrompts } from './load-prompts.ts';
 import { loadSite } from './load-site.ts';
 import { scoreGrokResponse } from './score.ts';
 
 const goldenRoot = join(dirname(fileURLToPath(import.meta.url)), '..');
 
+function provider(): LlmProvider {
+  return process.env.LLM_PROVIDER === 'openrouter' ? 'openrouter' : 'grok';
+}
+
 function key(): string | undefined {
-  const value = process.env.XAI_API_KEY;
+  const value = provider() === 'openrouter' ? process.env.OPENROUTER_API_KEY : process.env.XAI_API_KEY;
   return value !== undefined && value !== '' ? value : undefined;
 }
 
@@ -39,11 +43,14 @@ if (apiKey !== undefined) {
   }
   const site = loadSite(prompt.site);
   try {
-    const grok = await callGrok({
+    const grok = await callLlm({
+      provider: provider(),
       apiKey,
+      model: provider() === 'openrouter' ? process.env.OPENROUTER_MODEL : undefined,
       prompt: prompt.prompt,
       siteId: site.id,
       builder: detectBuilder(site),
+      pages: site.posts.map((post) => post.slug),
     });
     grokLive = {
       id: prompt.id,
@@ -57,7 +64,10 @@ if (apiKey !== undefined) {
 const report = {
   fixturePassed: fixtureScores.filter((row) => row.passed).length,
   fixtureTotal: fixtureScores.length,
-  grokLive: grokLive ?? { skipped: true, reason: 'XAI_API_KEY not set' },
+  grokLive: grokLive ?? {
+    skipped: true,
+    reason: provider() === 'openrouter' ? 'OPENROUTER_API_KEY not set' : 'XAI_API_KEY not set',
+  },
   scores: fixtureScores,
 };