Add Letta Code as a supported host

## Summary

Request to add [Letta Code](https://docs.letta.com/letta-code/index.md) as a supported host in gstack's declarative host config system.

Letta Code is an AI coding agent by [Letta Corporation](https://letta.com) — the team behind the open-source Letta framework for stateful LLM agents. It runs as a CLI (`letta`)
installed via `npm install -g @letta-ai/letta-code` and shares a similar skill format to Claude Code (markdown `SKILL.md` files with YAML frontmatter).

## Why

Letta Code is gaining traction as a coding agent with unique capabilities:
- **Persistent memory** — agents retain context across sessions via MemFS (git-backed memory filesystem)
- **Skills system** — `SKILL.md` files with `name` and `description` frontmatter, discovered and loaded on demand
- **Mods** — TypeScript mods at `~/.letta/mods/` that extend the harness with tools, commands, events, panels, and providers
- **Subagents** — agents can spawn specialized subagents for parallel work
- **Hooks** — `PreToolUse`, `Stop`, and other lifecycle hooks for safety and automation
- **Crons** — self-invocation for time-based task scheduling

Adding Letta Code as a host would let gstack's 23+ specialist skills (office-hours, plan-ceo-review, review, qa, ship, etc.) work with Letta Code, expanding gstack's reach to another AI
coding agent.

## Proposed Host Config

Based on `docs/ADDING_A_HOST.md`, here's a starting point for `hosts/letta.ts`:

```typescript
import type { HostConfig } from '../scripts/host-config';

const letta: HostConfig = {
name: 'letta',
displayName: 'Letta Code',
cliCommand: 'letta',
cliAliases: ['letta-code'],

globalRoot: '.letta/skills/gstack',
localSkillRoot: '.letta/skills/gstack',
hostSubdir: '.letta',
usesEnvVars: true,

frontmatter: {
mode: 'allowlist',
keepFields: ['name', 'description'],
descriptionLimit: null,
},

generation: {
generateMetadata: false,
skipSkills: ['codex'],
},

pathRewrites: [
{ from: '~/.claude/skills/gstack', to: '~/.letta/skills/gstack' },
{ from: '.claude/skills/gstack', to: '.letta/skills/gstack' },
{ from: '.claude/skills', to: '.letta/skills' },
],

runtimeRoot: {
globalSymlinks: ['bin', 'browse/dist', 'browse/bin', 'gstack-upgrade', 'ETHOS.md'],
globalFiles: { 'review': ['checklist.md', 'TODOS-format.md'] },
},

install: {
prefixable: false,
linkingStrategy: 'symlink-generated',
},

learningsMode: 'basic',
};

export default letta;

Letta Code specifics

│ Item │ Value │
├──────────────────┼──────────────────────────────────────────────────────────────────────────┤
│ CLI binary │ `letta` (installed via `npm install -g @letta-ai/letta-code`) │
│ Skills directory │ `~/.letta/skills/` (env-level, shared across agents) │
│ Skill format │ `SKILL.md` with YAML frontmatter (`name`, `description`) │
│ Project config │ `AGENTS.md` (equivalent of `CLAUDE.md`) │
│ Docs │ [docs.letta.com/letta-code](https://docs.letta.com/letta-code/index.md) │
│ GitHub │ [github.com/letta-ai/letta-code](https://github.com/letta-ai/letta-code) │

Skill format compatibility

Letta Code's SKILL.md format is nearly identical to Claude Code's:

---
name: skill-name
description: When to use this skill
---

# Skill content...

The frontmatter uses name and description — the same fields gstack's allowlist mode already keeps. No frontmatter transformation should be needed beyond the standard allowlist.

Tool name mapping

Letta Code's built-in tools use similar names to Claude Code:

│ Claude Code │ Letta Code │
├─────────────┼───────────────┤
│ Bash │ Bash │
│ Read │ Read │
│ Write │ Write │
│ Edit │ Edit │
│ Glob │ Glob │
│ Grep │ Grep │
│ WebSearch │ web_search │
│ WebFetch │ fetch_webpage │

Most tool references in gstack skills should work as-is or with minimal rewrites.

Checklist

- [ ] Create hosts/letta.ts with the config above
- [ ] Register in hosts/index.ts
- [ ] Add .letta/ to .gitignore
- [ ] Run bun run gen:skill-docs --host letta and verify output
- [ ] Verify no .claude/skills path leakage in generated docs
- [ ] Run bun test test/gen-skill-docs.test.ts and bun test test/host-config.test.ts
- [ ] Update README.md with Letta Code install instructions
- [ ] Add --host letta to the setup table

Install command (for README)

git clone --single-branch --depth 1 https://github.com/garrytan/gstack.git ~/gstack
cd ~/gstack && ./setup --host letta

Or from within Claude Code with gstack already installed:

Install gstack for Letta Code: run `cd ~/.claude/skills/gstack && ./setup --host letta`

Context

I'm a Letta Code user and would love to use gstack's workflow skills (especially /office-hours, /review, /qa, and /ship) with Letta Code. Happy to help test or contribute a PR if
there's interest.

Start with docs/ADDING_A_HOST.md and the existing host configs, then add the proposed integration in hosts/letta.ts and register it in hosts/index.ts. Run bun run gen:skill-docs --host letta, inspect generated paths for .claude/skills leakage, and run test/gen-skill-docs.test.ts and test/host-config.test.ts. Done includes the .gitignore and README.md setup updates from the checklist.

Written by the indexing model from the issue text.