feat(cli): implement /upgrade command (#21511)

packages/cli/src/services/BuiltinCommandLoader.ts

@@ -16,6 +16,7 @@ import {
   isNightly,
   startupProfiler,
   getAdminErrorMessage,
+  AuthType,
 } from '@google/gemini-cli-core';
 import { aboutCommand } from '../ui/commands/aboutCommand.js';
 import { agentsCommand } from '../ui/commands/agentsCommand.js';
@@ -59,6 +60,7 @@ import { shellsCommand } from '../ui/commands/shellsCommand.js';
 import { vimCommand } from '../ui/commands/vimCommand.js';
 import { setupGithubCommand } from '../ui/commands/setupGithubCommand.js';
 import { terminalSetupCommand } from '../ui/commands/terminalSetupCommand.js';
+import { upgradeCommand } from '../ui/commands/upgradeCommand.js';
 
 /**
  * Loads the core, hard-coded slash commands that are an integral part
@@ -223,6 +225,10 @@ export class BuiltinCommandLoader implements ICommandLoader {
       vimCommand,
       setupGithubCommand,
       terminalSetupCommand,
+      ...(this.config?.getContentGeneratorConfig()?.authType ===
+      AuthType.LOGIN_WITH_GOOGLE
+        ? [upgradeCommand]
+        : []),
     ];
     handle?.end();
     return allDefinitions.filter((cmd): cmd is SlashCommand => cmd !== null);