fix: improve loadCodeAssist for Google One AI Pro accounts

- Add separate LOAD_CODE_ASSIST_ENDPOINTS (prod first) and
  LOAD_CODE_ASSIST_HEADERS (google-api-nodejs-client User-Agent)
- Add duetProject to metadata for project discovery
- Silent fallback when API returns success but no project
  (matches opencode-antigravity-auth behavior)
- Only warn when all endpoints fail with actual errors

Fixes #114, addresses discussion #113

Co-Authored-By: Claude <noreply@anthropic.com>

src/constants.js

@@ -57,6 +57,25 @@ export const ANTIGRAVITY_HEADERS = {
     })
 };
 
+// Endpoint order for loadCodeAssist (prod first)
+// loadCodeAssist works better on prod for fresh/unprovisioned accounts
+export const LOAD_CODE_ASSIST_ENDPOINTS = [
+    ANTIGRAVITY_ENDPOINT_PROD,
+    ANTIGRAVITY_ENDPOINT_DAILY
+];
+
+// Hybrid headers specifically for loadCodeAssist
+// Uses google-api-nodejs-client User-Agent (required for project discovery on some accounts)
+export const LOAD_CODE_ASSIST_HEADERS = {
+    'User-Agent': 'google-api-nodejs-client/9.15.1',
+    'X-Goog-Api-Client': 'google-cloud-sdk vscode_cloudshelleditor/0.1',
+    'Client-Metadata': JSON.stringify({
+        ideType: 'IDE_UNSPECIFIED',
+        platform: 'PLATFORM_UNSPECIFIED',
+        pluginType: 'GEMINI'
+    })
+};
+
 // Default project ID if none can be discovered
 export const DEFAULT_PROJECT_ID = 'rising-fact-p41fc';
 
@@ -171,6 +190,8 @@ export const MODEL_FALLBACK_MAP = {
 export default {
     ANTIGRAVITY_ENDPOINT_FALLBACKS,
     ANTIGRAVITY_HEADERS,
+    LOAD_CODE_ASSIST_ENDPOINTS,
+    LOAD_CODE_ASSIST_HEADERS,
     DEFAULT_PROJECT_ID,
     TOKEN_REFRESH_INTERVAL_MS,
     REQUEST_BODY_LIMIT,