fix(plan): after exiting plan mode switches model to a flash model (#23885)

packages/core/src/config/config.ts

@@ -2413,6 +2413,7 @@ export class Config implements McpContext, AgentLoopContext {
 
     if (isPlanModeTransition || isYoloModeTransition) {
       if (this._geminiClient?.isInitialized()) {
+        this._geminiClient.clearCurrentSequenceModel();
         this._geminiClient.setTools().catch((err) => {
           debugLogger.error('Failed to update tools', err);
         });

packages/core/src/core/client.ts

@@ -132,6 +132,10 @@ export class GeminiClient {
     this.updateSystemInstruction();
   };
 
+  clearCurrentSequenceModel(): void {
+    this.currentSequenceModel = null;
+  }
+
   // Hook state to deduplicate BeforeAgent calls and track response for
   // AfterAgent
   private hookStateMap = new Map<