Add ModelChain support to ModelConfigService and make ModelDialog dynamic (#22914)

packages/core/src/services/modelConfigService.ts

@@ -5,6 +5,7 @@
  */
 
 import type { GenerateContentConfig } from '@google/genai';
+import type { ModelPolicy } from '../availability/modelPolicy.js';
 
 // The primary key for the ModelConfig is the model string. However, we also
 // support a secondary key to limit the override scope, typically an agent name.
@@ -111,6 +112,7 @@ export interface ModelConfigServiceConfig {
   modelDefinitions?: Record<string, ModelDefinition>;
   modelIdResolutions?: Record<string, ModelResolution>;
   classifierIdResolutions?: Record<string, ModelResolution>;
+  modelChains?: Record<string, ModelPolicy[]>;
 }
 
 const MAX_ALIAS_CHAIN_DEPTH = 100;
@@ -221,6 +223,29 @@ export class ModelConfigService {
     return resolution.default;
   }
 
+  getModelChain(chainName: string): ModelPolicy[] | undefined {
+    return this.config.modelChains?.[chainName];
+  }
+
+  /**
+   * Fetches a chain template and resolves all model IDs within it
+   * based on the provided context.
+   */
+  resolveChain(
+    chainName: string,
+    context: ResolutionContext = {},
+  ): ModelPolicy[] | undefined {
+    const template = this.config.modelChains?.[chainName];
+    if (!template) {
+      return undefined;
+    }
+    // Map through the template and resolve each model ID
+    return template.map((policy) => ({
+      ...policy,
+      model: this.resolveModelId(policy.model, context),
+    }));
+  }
+
   registerRuntimeModelConfig(aliasName: string, alias: ModelConfigAlias): void {
     this.runtimeAliases[aliasName] = alias;
   }