fix(credits): move credits fetch to extension side (#740)

* fix(credits): move credits fetch to extension side using install_id

Extension now reads `browseros.metrics_install_id` pref directly and fetches
credits from `llm.browseros.com` without going through the bundled server.
Unblocks the referral submit flow in prod without requiring a BrowserOS
binary release.

- Revert `/credits` route change that added `browserosId` to the response.
- Add `getOrCreateBrowserosId()` helper reading from BrowserOS prefs.
- Add `CREDITS_GATEWAY` to shared EXTERNAL_URLS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* refactor(credits): drop fallback UUID, read install_id directly

Extension only runs inside BrowserOS, so the prefs API is always available.
The chrome.storage fallback was dead code that would generate a ghost ID
diverging from the server's install_id anyway. Rename the helper to match
its simpler contract.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(credits): guard against empty install_id pref

Address Greptile P1 — throw instead of silently fetching `/credits/null`
when `browseros.metrics_install_id` is unset. Fails loudly so the broken
state is observable rather than masquerading as a credits outage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/browseros-agent/apps/agent/lib/credits/browseros-id.ts

@@ -0,0 +1,15 @@
+import { getBrowserOSAdapter } from '@/lib/browseros/adapter'
+import { BROWSEROS_PREFS } from '@/lib/browseros/prefs'
+
+// TODO(credits-identity): temporary shim — reuses the BrowserOS metrics
+// install_id as the credits/referral identifier. Replace with a dedicated
+// identity module once we have one.
+export async function getBrowserosId(): Promise<string> {
+  const adapter = getBrowserOSAdapter()
+  const pref = await adapter.getPref(BROWSEROS_PREFS.INSTALL_ID)
+  const id = pref.value
+  if (typeof id !== 'string' || id.length === 0) {
+    throw new Error('browseros.metrics_install_id is not set')
+  }
+  return id
+}

packages/browseros-agent/apps/agent/lib/credits/useCredits.ts

@@ -1,5 +1,6 @@
+import { EXTERNAL_URLS } from '@browseros/shared/constants/urls'
 import { useQuery, useQueryClient } from '@tanstack/react-query'
-import { getAgentServerUrl } from '@/lib/browseros/helpers'
+import { getBrowserosId } from './browseros-id'
 
 export interface CreditsInfo {
   credits: number
@@ -11,11 +12,14 @@ export interface CreditsInfo {
 const CREDITS_QUERY_KEY = ['credits']
 
 async function fetchCredits(): Promise<CreditsInfo> {
-  const baseUrl = await getAgentServerUrl()
-  const response = await fetch(`${baseUrl}/credits`)
+  const browserosId = await getBrowserosId()
+  const response = await fetch(
+    `${EXTERNAL_URLS.CREDITS_GATEWAY}/credits/${browserosId}`,
+  )
   if (!response.ok)
     throw new Error(`Failed to fetch credits: ${response.status}`)
-  return response.json()
+  const data = (await response.json()) as CreditsInfo
+  return { ...data, browserosId }
 }
 
 export function useCredits() {