feat(billing): implement G1 AI credits overage flow with billing telemetry (#18590)

packages/core/src/fallback/handler.ts

@@ -140,6 +140,9 @@ async function processIntent(
       // based on the availability service state (which is updated before this).
       return true;
 
+    case 'retry_with_credits':
+      return true;
+
     case 'stop':
       // Do not switch model on stop. User wants to stay on current model (and stop).
       return false;

packages/core/src/fallback/types.ts

@@ -17,6 +17,7 @@ import type {
 export type FallbackIntent =
   | 'retry_always' // Retry with fallback model and stick to it for future requests.
   | 'retry_once' // Retry with fallback model for this request only.
+  | 'retry_with_credits' // Retry the current request using Google One AI credits (and potentially future ones if strategy is 'always').
   | 'stop' // Switch to fallback for future requests, but stop the current request.
   | 'retry_later' // Stop the current request and do not fallback. Intend to try again later with the same model.
   | 'upgrade'; // Give user an option to upgrade the tier.