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/core/client.ts

@@ -262,6 +262,7 @@ export class GeminiClient {
     request: PartListUnion,
     signal: AbortSignal,
     turns: number = this.MAX_TURNS,
+    originalModel?: string,
   ): AsyncGenerator<ServerGeminiStreamEvent, Turn> {
     // Ensure turns never exceeds MAX_TURNS to prevent infinite loops
     const boundedTurns = Math.min(turns, this.MAX_TURNS);
@@ -269,6 +270,9 @@ export class GeminiClient {
       return new Turn(this.getChat());
     }
 
+    // Track the original model from the first call to detect model switching
+    const initialModel = originalModel || this.config.getModel();
+
     const compressed = await this.tryCompressChat();
     if (compressed) {
       yield { type: GeminiEventType.ChatCompressed, value: compressed };
@@ -279,6 +283,14 @@ export class GeminiClient {
       yield event;
     }
     if (!turn.pendingToolCalls.length && signal && !signal.aborted) {
+      // Check if model was switched during the call (likely due to quota error)
+      const currentModel = this.config.getModel();
+      if (currentModel !== initialModel) {
+        // Model was switched (likely due to quota error fallback)
+        // Don't continue with recursive call to prevent unwanted Flash execution
+        return turn;
+      }
+
       const nextSpeakerCheck = await checkNextSpeaker(
         this.getChat(),
         this,
@@ -288,7 +300,12 @@ export class GeminiClient {
         const nextRequest = [{ text: 'Please continue.' }];
         // This recursive call's events will be yielded out, but the final
         // turn object will be from the top-level call.
-        yield* this.sendMessageStream(nextRequest, signal, boundedTurns - 1);
+        yield* this.sendMessageStream(
+          nextRequest,
+          signal,
+          boundedTurns - 1,
+          initialModel,
+        );
       }
     }
     return turn;
@@ -298,9 +315,12 @@ export class GeminiClient {
     contents: Content[],
     schema: SchemaUnion,
     abortSignal: AbortSignal,
-    model: string = DEFAULT_GEMINI_FLASH_MODEL,
+    model?: string,
     config: GenerateContentConfig = {},
   ): Promise<Record<string, unknown>> {
+    // Use current model from config instead of hardcoded Flash model
+    const modelToUse =
+      model || this.config.getModel() || DEFAULT_GEMINI_FLASH_MODEL;
     try {
       const userMemory = this.config.getUserMemory();
       const systemInstruction = getCoreSystemPrompt(userMemory);
@@ -312,7 +332,7 @@ export class GeminiClient {
 
       const apiCall = () =>
         this.getContentGenerator().generateContent({
-          model,
+          model: modelToUse,
           config: {
             ...requestConfig,
             systemInstruction,
@@ -585,10 +605,14 @@ export class GeminiClient {
           fallbackModel,
           error,
         );
-        if (accepted) {
+        if (accepted !== false && accepted !== null) {
           this.config.setModel(fallbackModel);
           return fallbackModel;
         }
+        // Check if the model was switched manually in the handler
+        if (this.config.getModel() === fallbackModel) {
+          return null; // Model was switched but don't continue with current prompt
+        }
       } catch (error) {
         console.warn('Flash fallback handler failed:', error);
       }