feat(core): implement towards policy-driven model fallback mechanism (#13781)

packages/core/src/config/config.ts

@@ -59,6 +59,7 @@ import { StandardFileSystemService } from '../services/fileSystemService.js';
 import { logRipgrepFallback } from '../telemetry/loggers.js';
 import { RipgrepFallbackEvent } from '../telemetry/types.js';
 import type { FallbackModelHandler } from '../fallback/types.js';
+import { ModelAvailabilityService } from '../availability/modelAvailabilityService.js';
 import { ModelRouterService } from '../routing/modelRouterService.js';
 import { OutputFormat } from '../output/types.js';
 import type { ModelConfigServiceConfig } from '../services/modelConfigService.js';
@@ -347,6 +348,7 @@ export class Config {
   private geminiClient!: GeminiClient;
   private baseLlmClient!: BaseLlmClient;
   private modelRouterService: ModelRouterService;
+  private readonly modelAvailabilityService: ModelAvailabilityService;
   private readonly fileFiltering: {
     respectGitIgnore: boolean;
     respectGeminiIgnore: boolean;
@@ -483,6 +485,7 @@ export class Config {
     this.model = params.model;
     this.enableModelAvailabilityService =
       params.enableModelAvailabilityService ?? false;
+    this.modelAvailabilityService = new ModelAvailabilityService();
     this.previewFeatures = params.previewFeatures ?? undefined;
     this.maxSessionTurns = params.maxSessionTurns ?? -1;
     this.experimentalZedIntegration =
@@ -1044,6 +1047,10 @@ export class Config {
     return this.modelRouterService;
   }
 
+  getModelAvailabilityService(): ModelAvailabilityService {
+    return this.modelAvailabilityService;
+  }
+
   getEnableRecursiveFileSearch(): boolean {
     return this.fileFiltering.enableRecursiveFileSearch;
   }