feat(hosts): add pi as a supported host

Pi implements the Agent Skills spec, so gstack skills work with one config
file (no generator, setup, or tooling changes). Skills install to
~/.pi/agent/skills/gstack-*/ for global and .pi/skills/ for project-local,
both discovered by pi at startup.

- hosts/pi.ts: minimal config mirroring opencode pattern
- hosts/index.ts: register pi in ALL_HOST_CONFIGS + re-exports
- .gitignore: skip .pi/ (generated skill docs)
- README.md: add Pi row to host table + dedicated install section

.gitignore

@@ -16,6 +16,7 @@ bin/gstack-global-discover*
 .slate/
 .cursor/
 .openclaw/
+.pi/
 .hermes/
 .gbrain/
 .gbrain-source

README.md

@@ -120,11 +120,29 @@ Or target a specific agent with `./setup --host <name>`:
 | Slate | `--host slate` | `~/.slate/skills/gstack-*/` |
 | Kiro | `--host kiro` | `~/.kiro/skills/gstack-*/` |
 | Hermes | `--host hermes` | `~/.hermes/skills/gstack-*/` |
+| Pi | `--host pi` | `~/.pi/agent/skills/gstack-*/` |
 | GBrain (mod) | `--host gbrain` | `~/.gbrain/skills/gstack-*/` |
 
 **Want to add support for another agent?** See [docs/ADDING_A_HOST.md](docs/ADDING_A_HOST.md).
 It's one TypeScript config file, zero code changes.
 
+### Pi
+
+[Pi](https://pi.dev) implements the [Agent Skills standard](https://agentskills.io/specification)
+end-to-end, so every gstack skill works out of the box once the skills directory
+is configured. Install gstack into pi's global agent skills path:
+
+```bash
+git clone --single-branch --depth 1 https://github.com/garrytan/gstack.git ~/gstack
+cd ~/gstack && ./setup --host pi
+```
+
+Skills land at `~/.pi/agent/skills/gstack-*/`. For project-local skills (trusted
+project), pi also discovers `.pi/skills/`. Pi loads skill descriptions at startup
+and lazy-loads the full `SKILL.md` on demand, matching Claude Code's behavior.
+
+Invoke a skill with `/skill:<name>` (e.g. `/skill:review`, `/skill:ship`).
+
 ## See it work
 
 ```

hosts/index.ts

@@ -16,9 +16,10 @@ import cursor from './cursor';
 import openclaw from './openclaw';
 import hermes from './hermes';
 import gbrain from './gbrain';
+import pi from './pi';
 
 /** 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, pi];
 
 /** 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, pi };

hosts/pi.ts

@@ -0,0 +1,60 @@
+import type { HostConfig } from '../scripts/host-config';
+
+const pi: HostConfig = {
+  name: 'pi',
+  displayName: 'Pi',
+  cliCommand: 'pi',
+  cliAliases: [],
+
+  globalRoot: '.pi/agent/skills/gstack',
+  localSkillRoot: '.pi/skills/gstack',
+  hostSubdir: '.pi',
+  usesEnvVars: true,
+
+  frontmatter: {
+    mode: 'allowlist',
+    keepFields: ['name', 'description'],
+    descriptionLimit: 1024,
+  },
+
+  generation: {
+    generateMetadata: false,
+    skipSkills: ['codex'],
+  },
+
+  pathRewrites: [
+    { from: '~/.claude/skills/gstack', to: '~/.pi/agent/skills/gstack' },
+    { from: '.claude/skills/gstack', to: '.pi/skills/gstack' },
+    { from: '.claude/skills', to: '.pi/skills' },
+  ],
+  toolRewrites: {
+    'use the Bash tool': 'use the bash tool',
+    'use the Write tool': 'use the write tool',
+    'use the Read tool': 'use the read tool',
+    'use the Edit tool': 'use the edit tool',
+    'use the Grep tool': 'use the grep tool',
+    'use the Glob tool': 'use the find tool',
+    'use the Agent tool': 'use the agent tool',
+    'the Bash tool': 'the bash tool',
+    'the Read tool': 'the read tool',
+    'the Write tool': 'the write tool',
+    'the Edit tool': 'the edit tool',
+  },
+  suppressedResolvers: ['GBRAIN_CONTEXT_LOAD', 'GBRAIN_SAVE_RESULTS'],
+
+  runtimeRoot: {
+    globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'design/dist', 'gstack-upgrade', 'ETHOS.md', 'review/specialists', 'qa/templates', 'qa/references', 'plan-devex-review/dx-hall-of-fame.md'],
+    globalFiles: {
+      'review': ['checklist.md', 'design-checklist.md', 'greptile-triage.md', 'TODOS-format.md'],
+    },
+  },
+
+  install: {
+    prefixable: false,
+    linkingStrategy: 'symlink-generated',
+  },
+
+  learningsMode: 'basic',
+};
+
+export default pi;