feat: add /enhance command to improve user prompts

This adds the /enhance command which uses an LLM to refine user prompts
based on conversation history.

Closes #25133

.gemini/settings.json

@@ -1,11 +1,16 @@
 {
   "experimental": {
-    "plan": true,
     "extensionReloading": true,
     "modelSteering": true,
     "memoryManager": true
   },
   "general": {
-    "devtools": true
+    "devtools": true,
+    "plan": {
+      "enabled": true
+    }
+  },
+  "agents": {
+    "overrides": {}
   }
-}
+}

packages/cli/src/services/BuiltinCommandLoader.ts

@@ -31,6 +31,7 @@ import { corgiCommand } from '../ui/commands/corgiCommand.js';
 import { docsCommand } from '../ui/commands/docsCommand.js';
 import { directoryCommand } from '../ui/commands/directoryCommand.js';
 import { editorCommand } from '../ui/commands/editorCommand.js';
+import { enhanceCommand } from '../ui/commands/enhanceCommand.js';
 import { extensionsCommand } from '../ui/commands/extensionsCommand.js';
 import { footerCommand } from '../ui/commands/footerCommand.js';
 import { helpCommand } from '../ui/commands/helpCommand.js';
@@ -133,6 +134,7 @@ export class BuiltinCommandLoader implements ICommandLoader {
       docsCommand,
       directoryCommand,
       editorCommand,
+      enhanceCommand,
       ...(this.config?.getExtensionsEnabled() === false
         ? [
             {

packages/cli/src/test-utils/mockCommandContext.ts

@@ -58,6 +58,7 @@ export const createMockCommandContext = (
       pendingItem: null,
       setPendingItem: vi.fn(),
       loadHistory: vi.fn(),
+      setInput: vi.fn(),
       toggleCorgiMode: vi.fn(),
       toggleShortcutsHelp: vi.fn(),
       toggleVimEnabled: vi.fn(),

packages/cli/src/ui/commands/enhanceCommand.test.ts

@@ -0,0 +1,175 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, vi, type Mock } from 'vitest';
+import { enhanceCommand } from './enhanceCommand.js';
+import { type CommandContext } from './types.js';
+import { createMockCommandContext } from '../../test-utils/mockCommandContext.js';
+import { MessageType } from '../types.js';
+import { LlmRole } from '@google/gemini-cli-core';
+
+describe('enhanceCommand', () => {
+  let mockContext: CommandContext;
+  let mockGenerateContent: Mock;
+
+  beforeEach(() => {
+    mockGenerateContent = vi.fn();
+    mockContext = createMockCommandContext({
+      services: {
+        agentContext: {
+          promptId: 'test-prompt-id',
+          geminiClient: {
+            getHistory: vi.fn().mockReturnValue([
+              { role: 'user', parts: [{ text: 'previous user msg' }] },
+              { role: 'model', parts: [{ text: 'previous model msg' }] },
+            ]),
+          },
+          config: {
+            getModel: vi.fn().mockReturnValue('test-model'),
+            getContentGenerator: vi.fn().mockReturnValue({
+              generateContent: mockGenerateContent,
+            }),
+            getGemini31LaunchedSync: vi.fn().mockReturnValue(true),
+            getHasAccessToPreviewModel: vi.fn().mockReturnValue(true),
+          },
+        },
+      },
+      ui: {
+        addItem: vi.fn(),
+        setDebugMessage: vi.fn(),
+      },
+    } as unknown as CommandContext);
+  });
+
+  it('should have the correct name and description', () => {
+    expect(enhanceCommand.name).toBe('enhance');
+    expect(enhanceCommand.description).toBe(
+      'Enhance a prompt with additional context and rephrasing',
+    );
+  });
+
+  it('should show error if no prompt is provided', async () => {
+    if (!enhanceCommand.action) throw new Error('Action must be defined');
+
+    await enhanceCommand.action(mockContext, '');
+
+    expect(mockContext.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: expect.stringContaining('Please provide a prompt'),
+      }),
+    );
+  });
+
+  it('should call generateContent with correct parameters and show enhanced prompt', async () => {
+    if (!enhanceCommand.action) throw new Error('Action must be defined');
+
+    mockGenerateContent.mockResolvedValue({
+      candidates: [
+        {
+          content: {
+            parts: [{ text: 'Enhanced: do something' }],
+          },
+        },
+      ],
+    });
+
+    await enhanceCommand.action(mockContext, 'do something');
+
+    expect(mockGenerateContent).toHaveBeenCalledWith(
+      expect.objectContaining({
+        model: 'test-model',
+        contents: [
+          { role: 'user', parts: [{ text: 'previous user msg' }] },
+          { role: 'model', parts: [{ text: 'previous model msg' }] },
+          { role: 'user', parts: [{ text: 'do something' }] },
+        ],
+        config: {
+          systemInstruction: {
+            role: 'system',
+            parts: [
+              {
+                text: expect.stringContaining(
+                  "Generate an enhanced version of the user's prompt",
+                ),
+              },
+            ],
+          },
+        },
+      }),
+      'test-prompt-id',
+      LlmRole.UTILITY_TOOL,
+    );
+
+    expect(mockContext.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.INFO,
+        text: expect.stringContaining(
+          'Enhanced prompt:\n\nEnhanced: do something',
+        ),
+      }),
+    );
+    expect(mockContext.ui.setInput).toHaveBeenCalledWith(
+      'Enhanced: do something',
+    );
+  });
+
+  it('should clean the response from markdown and quotes', async () => {
+    if (!enhanceCommand.action) throw new Error('Action must be defined');
+
+    mockGenerateContent.mockResolvedValue({
+      candidates: [
+        {
+          content: {
+            parts: [{ text: '```markdown\n"Clean me"\n```' }],
+          },
+        },
+      ],
+    });
+
+    await enhanceCommand.action(mockContext, 'dirty prompt');
+
+    expect(mockContext.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.INFO,
+        text: expect.stringContaining('Enhanced prompt:\n\nClean me'),
+      }),
+    );
+    expect(mockContext.ui.setInput).toHaveBeenCalledWith('Clean me');
+  });
+
+  it('should handle API errors gracefully', async () => {
+    if (!enhanceCommand.action) throw new Error('Action must be defined');
+
+    mockGenerateContent.mockRejectedValue(new Error('API Error'));
+
+    await enhanceCommand.action(mockContext, 'test prompt');
+
+    expect(mockContext.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: expect.stringContaining('Failed to enhance prompt: API Error'),
+      }),
+    );
+  });
+
+  it('should handle empty response from model', async () => {
+    if (!enhanceCommand.action) throw new Error('Action must be defined');
+
+    mockGenerateContent.mockResolvedValue({
+      candidates: [],
+    });
+
+    await enhanceCommand.action(mockContext, 'test prompt');
+
+    expect(mockContext.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: expect.stringContaining('Empty response from model'),
+      }),
+    );
+  });
+});

packages/cli/src/ui/commands/enhanceCommand.ts

@@ -0,0 +1,104 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { CommandKind, type SlashCommand } from './types.js';
+import { MessageType } from '../types.js';
+import { LlmRole, resolveModel } from '@google/gemini-cli-core';
+import type { Content } from '@google/genai';
+
+const INSTRUCTION =
+  "Generate an enhanced version of the user's prompt, using the preceding conversation as context. Reply with ONLY the enhanced prompt - no conversation, explanations, lead-in, bullet points, placeholders, or surrounding quotes.";
+
+function clean(text: string) {
+  const stripped = text.replace(/^```\w*\n?|```$/g, '').trim();
+  return stripped.replace(/^(['"])([\s\S]*)\1$/, '$2').trim();
+}
+
+export const enhanceCommand: SlashCommand = {
+  name: 'enhance',
+  description: 'Enhance a prompt with additional context and rephrasing',
+  kind: CommandKind.BUILT_IN,
+  autoExecute: true,
+  action: async (context, args) => {
+    const draft = args.trim();
+    if (!draft) {
+      context.ui.addItem({
+        type: MessageType.ERROR,
+        text: 'Please provide a prompt to enhance. Usage: /enhance <prompt>',
+      });
+      return;
+    }
+
+    const agentContext = context.services.agentContext;
+    if (!agentContext) {
+      context.ui.addItem({
+        type: MessageType.ERROR,
+        text: 'Agent context not available.',
+      });
+      return;
+    }
+
+    const config = agentContext.config;
+    const contentGenerator = config.getContentGenerator();
+    const promptId = agentContext.promptId;
+
+    const model = resolveModel(
+      config.getModel(),
+      config.getGemini31LaunchedSync?.() ?? false,
+      false,
+      config.getHasAccessToPreviewModel?.() ?? true,
+      config,
+    );
+
+    context.ui.setDebugMessage('Enhancing prompt...');
+
+    try {
+      const history = agentContext.geminiClient?.getHistory() ?? [];
+      const contents: Content[] = [
+        ...history,
+        { role: 'user', parts: [{ text: draft }] },
+      ];
+
+      const response = await contentGenerator.generateContent(
+        {
+          model,
+          contents,
+          config: {
+            systemInstruction: {
+              role: 'system',
+              parts: [{ text: INSTRUCTION }],
+            },
+          },
+        },
+        promptId,
+        LlmRole.UTILITY_TOOL,
+      );
+
+      const enhancedText = response.candidates?.[0]?.content?.parts?.[0]?.text;
+
+      if (enhancedText) {
+        const cleanedText = clean(enhancedText);
+        context.ui.addItem({
+          type: MessageType.INFO,
+          text: `Enhanced prompt:\n\n${cleanedText}`,
+        });
+        context.ui.setInput(cleanedText);
+      } else {
+        context.ui.addItem({
+          type: MessageType.ERROR,
+          text: 'Failed to enhance prompt: Empty response from model.',
+        });
+      }
+    } catch (error) {
+      context.ui.addItem({
+        type: MessageType.ERROR,
+        text: `Failed to enhance prompt: ${error instanceof Error ? error.message : String(error)}`,
+      });
+    } finally {
+      context.ui.setDebugMessage('');
+    }
+  },
+};

packages/cli/src/ui/commands/types.ts

@@ -70,6 +70,12 @@ export interface CommandContext {
      * @param postLoadInput Optional text to set in the input buffer after loading history.
      */
     loadHistory: (history: HistoryItem[], postLoadInput?: string) => void;
+    /**
+     * Sets the text in the input buffer.
+     *
+     * @param text The text to set.
+     */
+    setInput: (text: string) => void;
     /** Toggles a special display mode. */
     toggleCorgiMode: () => void;
     toggleDebugProfiler: () => void;

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -228,6 +228,7 @@ export const useSlashCommandProcessor = (
             actions.setText(postLoadInput);
           }
         },
+        setInput: (text) => actions.setText(text),
         setDebugMessage: actions.setDebugMessage,
         pendingItem,
         setPendingItem,

packages/cli/src/ui/noninteractive/nonInteractiveUi.ts

@@ -29,6 +29,7 @@ export function createNonInteractiveUI(): CommandContext['ui'] {
     clear: () => {},
     setDebugMessage: (_message) => {},
     loadHistory: (_newHistory) => {},
+    setInput: (_text) => {},
     pendingItem: null,
     setPendingItem: (_item) => {},
     toggleCorgiMode: () => {},