feat: register Gemini CLI host with dedicated .gemini subdir

Wire the previously-unregistered Gemini CLI HostConfig into the registry.
The rescued config reused Codex's .agents hostSubdir, which collides with
codex under validateAllConfigs (hostSubdir/globalRoot must be unique).
Retarget Gemini to its native .gemini home (matching its GEMINI.md rewrite
and Google's Gemini CLI convention) and bump the host-count assertion 10 -> 11.

hosts/gemini.ts

@@ -0,0 +1,70 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const gemini: HostConfig = {
+  name: 'gemini',
+  displayName: 'Gemini CLI',
+  cliCommand: 'gemini',
+  cliAliases: ['gemini-cli'],
+
+  globalRoot: '.gemini/skills/gstack',
+  localSkillRoot: '.gemini/skills/gstack',
+  hostSubdir: '.gemini',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description'],
+    descriptionLimit: null,
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: ['codex'],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '~/.gemini/skills/gstack' },
+    { from: '.claude/skills/gstack', to: '.gemini/skills/gstack' },
+    { from: '.claude/skills', to: '.gemini/skills' },
+    { from: 'CLAUDE.md', to: 'GEMINI.md' },
+  ],
+
+  toolRewrites: {
+    'use the Bash tool': 'use the run_shell_command tool',
+    'use the Write tool': 'use the write_file tool',
+    'use the Read tool': 'use the read_file tool',
+    'use the Edit tool': 'use the replace_in_file tool',
+    'use the Agent tool': 'use delegate_to_agent',
+    'use the Glob tool': 'use the list_directory tool',
+    'use the Grep tool': 'use the search_files tool',
+    'the Bash tool': 'the run_shell_command tool',
+    'the Read tool': 'the read_file tool',
+    'the Write tool': 'the write_file tool',
+    'the Edit tool': 'the replace_in_file tool',
+  },
+
+  suppressedResolvers: [
+    'DESIGN_OUTSIDE_VOICES',
+    'ADVERSARIAL_STEP',
+    'CODEX_SECOND_OPINION',
+    'CODEX_PLAN_REVIEW',
+    'REVIEW_ARMY',
+  ],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'TODOS-format.md'],
+    },
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  coAuthorTrailer: 'Co-Authored-By: Gemini CLI <noreply@google.com>',
+  learningsMode: 'basic',
+};
+
+export default gemini;

hosts/index.ts

@@ -16,9 +16,10 @@ import cursor from './cursor';
 import openclaw from './openclaw';
 import hermes from './hermes';
 import gbrain from './gbrain';
+import gemini from './gemini';
 
 /** All registered host configs. Add new hosts here. */
-export const ALL_HOST_CONFIGS: HostConfig[] = [claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain];
+export const ALL_HOST_CONFIGS: HostConfig[] = [claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain, gemini];
 
 /** Map from host name to config. */
 export const HOST_CONFIG_MAP: Record<string, HostConfig> = Object.fromEntries(
@@ -65,4 +66,4 @@ export function getExternalHosts(): HostConfig[] {
 }
 
 // Re-export individual configs for direct import
-export { claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain };
+export { claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain, gemini };

test/host-config.test.ts

@@ -30,8 +30,8 @@ const ROOT = path.resolve(import.meta.dir, '..');
 // ─── hosts/index.ts ─────────────────────────────────────────
 
 describe('hosts/index.ts', () => {
-  test('ALL_HOST_CONFIGS has 10 hosts', () => {
-    expect(ALL_HOST_CONFIGS.length).toBe(10);
+  test('ALL_HOST_CONFIGS has 11 hosts', () => {
+    expect(ALL_HOST_CONFIGS.length).toBe(11);
   });
 
   test('ALL_HOST_NAMES matches config names', () => {