feat(core): Plumbing for late resolution of model configs. (#14597)

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

@@ -1344,6 +1344,30 @@ describe('Generation Config Merging (HACK)', () => {
     expect(serviceConfig.overrides).toEqual(userOverrides);
   });
 
+  it('should merge default overrides when user provides only aliases', () => {
+    const userAliases = {
+      'my-alias': {
+        modelConfig: { model: 'my-model' },
+      },
+    };
+
+    const params: ConfigParameters = {
+      ...baseParams,
+      modelConfigServiceConfig: {
+        aliases: userAliases,
+      },
+    };
+
+    const config = new Config(params);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const serviceConfig = (config.modelConfigService as any).config;
+
+    // Assert that the user's aliases are present
+    expect(serviceConfig.aliases).toEqual(userAliases);
+    // Assert that the default overrides are present
+    expect(serviceConfig.overrides).toEqual(DEFAULT_MODEL_CONFIGS.overrides);
+  });
+
   it('should use user-provided aliases if they exist', () => {
     const userAliases = {
       'my-alias': {

packages/core/src/config/config.ts

@@ -629,11 +629,19 @@ export class Config {
     // TODO(12593): Fix the settings loading logic to properly merge defaults and
     // remove this hack.
     let modelConfigServiceConfig = params.modelConfigServiceConfig;
-    if (modelConfigServiceConfig && !modelConfigServiceConfig.aliases) {
-      modelConfigServiceConfig = {
-        ...modelConfigServiceConfig,
-        aliases: DEFAULT_MODEL_CONFIGS.aliases,
-      };
+    if (modelConfigServiceConfig) {
+      if (!modelConfigServiceConfig.aliases) {
+        modelConfigServiceConfig = {
+          ...modelConfigServiceConfig,
+          aliases: DEFAULT_MODEL_CONFIGS.aliases,
+        };
+      }
+      if (!modelConfigServiceConfig.overrides) {
+        modelConfigServiceConfig = {
+          ...modelConfigServiceConfig,
+          overrides: DEFAULT_MODEL_CONFIGS.overrides,
+        };
+      }
     }
 
     this.modelConfigService = new ModelConfigService(

packages/core/src/config/defaultModelConfigs.ts

@@ -209,4 +209,14 @@ export const DEFAULT_MODEL_CONFIGS: ModelConfigServiceConfig = {
       },
     },
   },
+  overrides: [
+    {
+      match: { model: 'chat-base', isRetry: true },
+      modelConfig: {
+        generateContentConfig: {
+          temperature: 1,
+        },
+      },
+    },
+  ],
 };