Remove auto-execution on Flash in the event of a 429/Quota failover (#3662)

Co-authored-by: Jenna Inouye <jinouye@google.com>

packages/core/src/config/config.ts

@@ -104,7 +104,7 @@ export type FlashFallbackHandler = (
   currentModel: string,
   fallbackModel: string,
   error?: unknown,
-) => Promise<boolean>;
+) => Promise<boolean | string | null>;
 
 export interface ConfigParameters {
   sessionId: string;
@@ -183,6 +183,7 @@ export class Config {
   private readonly listExtensions: boolean;
   private readonly _activeExtensions: ActiveExtension[];
   flashFallbackHandler?: FlashFallbackHandler;
+  private quotaErrorOccurred: boolean = false;
 
   constructor(params: ConfigParameters) {
     this.sessionId = params.sessionId;
@@ -304,6 +305,14 @@ export class Config {
     this.flashFallbackHandler = handler;
   }
 
+  setQuotaErrorOccurred(value: boolean): void {
+    this.quotaErrorOccurred = value;
+  }
+
+  getQuotaErrorOccurred(): boolean {
+    return this.quotaErrorOccurred;
+  }
+
   getEmbeddingModel(): string {
     return this.embeddingModel;
   }