ui(cli): display small tag for nightly/preview versions

This PR implements a more compact version display in the AppHeader, as requested in Issue #21373. Long pre-release version strings (e.g., `0.42.0-nightly.20260428.g59b2dea0e`) are now parsed to show the base version followed by a small bracketed tag (e.g., `v0.42.0 [nightly]`).

Changes:
- Modified `AppHeader.tsx` to parse version strings for pre-release tags (`nightly`, `preview`, `alpha`, `beta`, `rc`).
- Added `AppHeaderVersion.test.tsx` to verify the new rendering logic for various version formats.

This makes the header cleaner, especially on narrower terminals where long version strings could cause layout issues.

cc @jacob314 @keithguerin
labels: bot-fix

packages/cli/src/ui/components/AppHeader.tsx

@@ -107,36 +107,53 @@ export const AppHeader = ({ version, showDetails = true }: AppHeaderProps) => {
     </Box>
   );
 
-  const renderMetadata = (isBelow = false) => (
-    <Box marginLeft={isBelow ? 0 : 2} flexDirection="column">
-      {/* Line 1: Gemini CLI vVersion [Updating] */}
-      <Box>
-        <Text bold color={theme.text.primary}>
-          Gemini CLI
-        </Text>
-        <Text color={theme.text.secondary}> v{version}</Text>
-        {updateInfo?.isUpdating && (
-          <Box marginLeft={2}>
-            <Text color={theme.text.secondary}>
-              <CliSpinner /> Updating
-            </Text>
-          </Box>
+  const renderMetadata = (isBelow = false) => {
+    // Parse version for a "small tag" if it's a long pre-release string (e.g. nightly)
+    // Example: 0.42.0-nightly.20260428.g59b2dea0e -> v0.42.0 [nightly]
+    let displayVersion = version;
+    let tag = '';
+
+    const tagMatch = version.match(/^(.+)-(nightly|preview|alpha|beta|rc)(\..+)?$/);
+
+    if (tagMatch) {
+      displayVersion = tagMatch[1];
+      tag = tagMatch[2];
+    }
+
+    return (
+      <Box marginLeft={isBelow ? 0 : 2} flexDirection="column">
+        {/* Line 1: Gemini CLI vVersion [tag] [Updating] */}
+        <Box>
+          <Text bold color={theme.text.primary}>
+            Gemini CLI
+          </Text>
+          <Text color={theme.text.secondary}> v{displayVersion}</Text>
+          {tag && (
+            <Text color={theme.text.secondary}> {`[${tag}]`}</Text>
+          )}
+          {updateInfo?.isUpdating && (
+            <Box marginLeft={2}>
+              <Text color={theme.text.secondary}>
+                <CliSpinner /> Updating
+              </Text>
+            </Box>
+          )}
+        </Box>
+
+        {showDetails && (
+          <>
+            {/* Line 2: Blank */}
+            <Box height={1} />
+
+            {/* Lines 3 & 4: User Identity info (Email /auth and Plan /upgrade) */}
+            {settings.merged.ui.showUserIdentity !== false && (
+              <UserIdentity config={config} />
+            )}
+          </>
         )}
       </Box>
-
-      {showDetails && (
-        <>
-          {/* Line 2: Blank */}
-          <Box height={1} />
-
-          {/* Lines 3 & 4: User Identity info (Email /auth and Plan /upgrade) */}
-          {settings.merged.ui.showUserIdentity !== false && (
-            <UserIdentity config={config} />
-          )}
-        </>
-      )}
-    </Box>
-  );
+    );
+  };
 
   const useColumnLayout = !!logoTextArt || isNarrow;
 

packages/cli/src/ui/components/AppHeaderVersion.test.tsx

@@ -0,0 +1,51 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { renderWithProviders } from '../../test-utils/render.js';
+import { AppHeader } from './AppHeader.js';
+import { describe, it, expect, vi } from 'vitest';
+
+// Mock dependencies to avoid complex setup
+vi.mock('@google/gemini-cli-core', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('@google/gemini-cli-core')>();
+  return {
+    ...actual,
+    isAppleTerminal: () => false,
+  };
+});
+
+describe('AppHeader Version Rendering', () => {
+  it('renders nightly version with a small tag instead of long string', async () => {
+    const version = '0.42.0-nightly.20260428.g59b2dea0e';
+    const { lastFrame } = await renderWithProviders(
+      <AppHeader version={version} />
+    );
+
+    // Desired: Gemini CLI v0.42.0 [nightly]
+    expect(lastFrame()).toContain('Gemini CLI v0.42.0 [nightly]');
+    expect(lastFrame()).not.toContain(version);
+  });
+
+  it('renders preview version with a small tag', async () => {
+    const version = '0.42.0-preview.1';
+    const { lastFrame } = await renderWithProviders(
+      <AppHeader version={version} />
+    );
+
+    expect(lastFrame()).toContain('Gemini CLI v0.42.0 [preview]');
+    expect(lastFrame()).not.toContain(version);
+  });
+
+  it('renders standard version without tag', async () => {
+    const version = '0.42.0';
+    const { lastFrame } = await renderWithProviders(
+      <AppHeader version={version} />
+    );
+
+    expect(lastFrame()).toContain('Gemini CLI v0.42.0');
+    expect(lastFrame()).not.toContain('[');
+  });
+});