fix(core): use hasAccessToPreview for auto model resolution and fix disappearing models (#27112)

packages/core/src/config/config.test.ts

@@ -2019,7 +2019,6 @@ describe('Server Config (config.ts)', () => {
     expect(configInternal.lastEmittedQuotaRemaining).toBeUndefined();
     expect(configInternal.lastEmittedQuotaLimit).toBeUndefined();
     expect(configInternal.lastQuotaFetchTime).toBe(0);
-    expect(configInternal.hasAccessToPreviewModel).toBeNull();
 
     // Event emission
     expect(emitQuotaSpy).toHaveBeenCalledWith(undefined, undefined, undefined);

packages/core/src/config/config.ts

@@ -1833,7 +1833,6 @@ export class Config implements McpContext, AgentLoopContext {
     this.modelQuotas.clear();
     this.lastRetrievedQuota = undefined;
     this.lastQuotaFetchTime = 0;
-    this.hasAccessToPreviewModel = null;
 
     // Force an event emission to clear the UI display
     coreEvents.emitQuotaChanged(undefined, undefined, undefined);

packages/core/src/config/models.ts

@@ -164,7 +164,7 @@ export function resolveModel(
   switch (normalizedModel) {
     case GEMINI_MODEL_ALIAS_AUTO:
     case GEMINI_MODEL_ALIAS_PRO: {
-      if (currentReleaseChannel === 'stable') {
+      if (!hasAccessToPreview) {
         resolved = DEFAULT_GEMINI_MODEL;
         break;
       }