fix(patch): cherry-pick 37f128a to release/v0.28.0-preview.6-pr-18478 [CONFLICTS] (#18732)

Co-authored-by: matt korwel <matt.korwel@gmail.com>

packages/core/src/routing/strategies/numericalClassifierStrategy.ts

@@ -12,7 +12,7 @@ import type {
   RoutingDecision,
   RoutingStrategy,
 } from '../routingStrategy.js';
-import { resolveClassifierModel } from '../../config/models.js';
+import { resolveClassifierModel, isGemini3Model } from '../../config/models.js';
 import { createUserContent, Type } from '@google/genai';
 import type { Config } from '../../config/config.js';
 import { debugLogger } from '../../utils/debugLogger.js';
@@ -134,10 +134,15 @@ export class NumericalClassifierStrategy implements RoutingStrategy {
   ): Promise<RoutingDecision | null> {
     const startTime = Date.now();
     try {
+      const model = context.requestedModel ?? config.getModel();
       if (!(await config.getNumericalRoutingEnabled())) {
         return null;
       }
 
+      if (!isGemini3Model(model, config.getPreviewFeatures())) {
+        return null;
+      }
+
       const promptId = getPromptIdWithFallback('classifier-router');
 
       const finalHistory = context.history.slice(-HISTORY_TURNS_FOR_CONTEXT);
@@ -177,7 +182,7 @@ export class NumericalClassifierStrategy implements RoutingStrategy {
         );
 
       const selectedModel = resolveClassifierModel(
-        config.getModel(),
+        model,
         modelAlias,
         config.getPreviewFeatures(),
       );