feat: automatic /model persistence across Gemini CLI sessions (#13199)

Co-authored-by: Jack Wotherspoon <jackwoth@google.com>

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

@@ -1629,6 +1629,18 @@ describe('Config getHooks', () => {
       expect(config.getModel()).toBe(originalModel);
       expect(config.getActiveModel()).toBe(originalModel);
     });
+
+    it('should call onModelChange when a new model is set', () => {
+      const onModelChange = vi.fn();
+      const config = new Config({
+        ...baseParams,
+        onModelChange,
+      });
+
+      config.setModel(DEFAULT_GEMINI_MODEL);
+
+      expect(onModelChange).toHaveBeenCalledWith(DEFAULT_GEMINI_MODEL);
+    });
   });
 });
 

packages/core/src/config/config.ts

@@ -337,6 +337,7 @@ export interface ConfigParameters {
   previewFeatures?: boolean;
   enableAgents?: boolean;
   experimentalJitContext?: boolean;
+  onModelChange?: (model: string) => void;
 }
 
 export class Config {
@@ -457,6 +458,7 @@ export class Config {
   private experiments: Experiments | undefined;
   private experimentsPromise: Promise<void> | undefined;
   private hookSystem?: HookSystem;
+  private readonly onModelChange: ((model: string) => void) | undefined;
 
   private readonly enableAgents: boolean;
 
@@ -623,6 +625,7 @@ export class Config {
     this.disableYoloMode = params.disableYoloMode ?? false;
     this.hooks = params.hooks;
     this.experiments = params.experiments;
+    this.onModelChange = params.onModelChange;
 
     if (params.contextFileName) {
       setGeminiMdFilename(params.contextFileName);
@@ -879,6 +882,9 @@ export class Config {
       // When the user explicitly sets a model, that becomes the active model.
       this._activeModel = newModel;
       coreEvents.emitModelChanged(newModel);
+      if (this.onModelChange) {
+        this.onModelChange(newModel);
+      }
     }
     this.modelAvailabilityService.reset();
   }