3 files changed, 215 insertions, 5 deletions
diff --git a/packages/cli/src/ui/commands/compressCommand.test.ts b/packages/cli/src/ui/commands/compressCommand.test.ts
new file mode 100644
index 00000000..95a8bda3
--- /dev/null
+++ b/packages/cli/src/ui/commands/compressCommand.test.ts
@@ -0,0 +1,129 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { GeminiClient } from '@google/gemini-cli-core';
+import { vi, describe, it, expect, beforeEach } from 'vitest';
+import { compressCommand } from './compressCommand.js';
+import { createMockCommandContext } from '../../test-utils/mockCommandContext.js';
+import { MessageType } from '../types.js';
+
+describe('compressCommand', () => {
+  let context: ReturnType<typeof createMockCommandContext>;
+  let mockTryCompressChat: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    mockTryCompressChat = vi.fn();
+    context = createMockCommandContext({
+      services: {
+        config: {
+          getGeminiClient: () =>
+            ({
+              tryCompressChat: mockTryCompressChat,
+            }) as unknown as GeminiClient,
+        },
+      },
+    });
+  });
+
+  it('should do nothing if a compression is already pending', async () => {
+    context.ui.pendingItem = {
+      type: MessageType.COMPRESSION,
+      compression: {
+        isPending: true,
+        originalTokenCount: null,
+        newTokenCount: null,
+      },
+    };
+    await compressCommand.action!(context, '');
+    expect(context.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: 'Already compressing, wait for previous request to complete',
+      }),
+      expect.any(Number),
+    );
+    expect(context.ui.setPendingItem).not.toHaveBeenCalled();
+    expect(mockTryCompressChat).not.toHaveBeenCalled();
+  });
+
+  it('should set pending item, call tryCompressChat, and add result on success', async () => {
+    const compressedResult = {
+      originalTokenCount: 200,
+      newTokenCount: 100,
+    };
+    mockTryCompressChat.mockResolvedValue(compressedResult);
+
+    await compressCommand.action!(context, '');
+
+    expect(context.ui.setPendingItem).toHaveBeenNthCalledWith(
+      1,
+      expect.objectContaining({
+        type: MessageType.COMPRESSION,
+        compression: {
+          isPending: true,
+          originalTokenCount: null,
+          newTokenCount: null,
+        },
+      }),
+    );
+
+    expect(mockTryCompressChat).toHaveBeenCalledWith(
+      expect.stringMatching(/^compress-\d+$/),
+      true,
+    );
+
+    expect(context.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.COMPRESSION,
+        compression: {
+          isPending: false,
+          originalTokenCount: 200,
+          newTokenCount: 100,
+        },
+      }),
+      expect.any(Number),
+    );
+
+    expect(context.ui.setPendingItem).toHaveBeenNthCalledWith(2, null);
+  });
+
+  it('should add an error message if tryCompressChat returns falsy', async () => {
+    mockTryCompressChat.mockResolvedValue(null);
+
+    await compressCommand.action!(context, '');
+
+    expect(context.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: 'Failed to compress chat history.',
+      }),
+      expect.any(Number),
+    );
+    expect(context.ui.setPendingItem).toHaveBeenCalledWith(null);
+  });
+
+  it('should add an error message if tryCompressChat throws', async () => {
+    const error = new Error('Compression failed');
+    mockTryCompressChat.mockRejectedValue(error);
+
+    await compressCommand.action!(context, '');
+
+    expect(context.ui.addItem).toHaveBeenCalledWith(
+      expect.objectContaining({
+        type: MessageType.ERROR,
+        text: `Failed to compress chat history: ${error.message}`,
+      }),
+      expect.any(Number),
+    );
+    expect(context.ui.setPendingItem).toHaveBeenCalledWith(null);
+  });
+
+  it('should clear the pending item in a finally block', async () => {
+    mockTryCompressChat.mockRejectedValue(new Error('some error'));
+    await compressCommand.action!(context, '');
+    expect(context.ui.setPendingItem).toHaveBeenCalledWith(null);
+  });
+});
diff --git a/packages/cli/src/ui/commands/compressCommand.ts b/packages/cli/src/ui/commands/compressCommand.ts
new file mode 100644
index 00000000..c3dfdf37
--- /dev/null
+++ b/packages/cli/src/ui/commands/compressCommand.ts
@@ -0,0 +1,77 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { HistoryItemCompression, MessageType } from '../types.js';
+import { SlashCommand } from './types.js';
+
+export const compressCommand: SlashCommand = {
+  name: 'compress',
+  altName: 'summarize',
+  description: 'Compresses the context by replacing it with a summary.',
+  action: async (context) => {
+    const { ui } = context;
+    if (ui.pendingItem) {
+      ui.addItem(
+        {
+          type: MessageType.ERROR,
+          text: 'Already compressing, wait for previous request to complete',
+        },
+        Date.now(),
+      );
+      return;
+    }
+
+    const pendingMessage: HistoryItemCompression = {
+      type: MessageType.COMPRESSION,
+      compression: {
+        isPending: true,
+        originalTokenCount: null,
+        newTokenCount: null,
+      },
+    };
+
+    try {
+      ui.setPendingItem(pendingMessage);
+      const promptId = `compress-${Date.now()}`;
+      const compressed = await context.services.config
+        ?.getGeminiClient()
+        ?.tryCompressChat(promptId, true);
+      if (compressed) {
+        ui.addItem(
+          {
+            type: MessageType.COMPRESSION,
+            compression: {
+              isPending: false,
+              originalTokenCount: compressed.originalTokenCount,
+              newTokenCount: compressed.newTokenCount,
+            },
+          } as HistoryItemCompression,
+          Date.now(),
+        );
+      } else {
+        ui.addItem(
+          {
+            type: MessageType.ERROR,
+            text: 'Failed to compress chat history.',
+          },
+          Date.now(),
+        );
+      }
+    } catch (e) {
+      ui.addItem(
+        {
+          type: MessageType.ERROR,
+          text: `Failed to compress chat history: ${
+            e instanceof Error ? e.message : String(e)
+          }`,
+        },
+        Date.now(),
+      );
+    } finally {
+      ui.setPendingItem(null);
+    }
+  },
+};
diff --git a/packages/cli/src/ui/commands/types.ts b/packages/cli/src/ui/commands/types.ts
index 27db2be2..85a85abe 100644
--- a/packages/cli/src/ui/commands/types.ts
+++ b/packages/cli/src/ui/commands/types.ts
@@ -23,11 +23,6 @@ export interface CommandContext {
   };
   // UI state and history management
   ui: {
-    // TODO - As more commands are add some additions may be needed or reworked using this new context.
-    // Ex.
-    // history: HistoryItem[];
-    // pendingHistoryItems: HistoryItemWithoutId[];
-
     /** Adds a new item to the history display. */
     addItem: UseHistoryManagerReturn['addItem'];
     /** Clears all history items and the console screen. */
@@ -36,6 +31,15 @@ export interface CommandContext {
      * Sets the transient debug message displayed in the application footer in debug mode.
      */
     setDebugMessage: (message: string) => void;
+    /** The currently pending history item, if any. */
+    pendingItem: HistoryItemWithoutId | null;
+    /**
+     * Sets a pending item in the history, which is useful for indicating
+     * that a long-running operation is in progress.
+     *
+     * @param item The history item to display as pending, or `null` to clear.
+     */
+    setPendingItem: (item: HistoryItemWithoutId | null) => void;
   };
   // Session-specific data
   session: {