gstack/docs/ADDING_A_HOST.md

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# Adding a New Host to gstack
gstack uses a declarative host config system. Each supported AI coding agent
(Claude, Codex, Factory, Kiro, OpenCode, Slate, Cursor, OpenClaw, Hermes,
GBrain) is defined as a typed TypeScript config object built by the
`defineHost()` factory. Adding a new host means creating one file and
re-exporting it. Zero code changes to the generator, setup, or tooling.
## How it works
```
hosts/
├── define-host.ts # defineHost() factory: shared defaults + derived fields
├── claude.ts # Primary host
├── codex.ts # OpenAI Codex CLI
├── factory.ts # Factory Droid
├── kiro.ts # Amazon Kiro
├── opencode.ts # OpenCode
├── slate.ts # Slate (Random Labs)
├── cursor.ts # Cursor
├── openclaw.ts # OpenClaw
├── hermes.ts # Hermes (Nous Research)
├── gbrain.ts # GBrain
└── index.ts # Registry: imports all, derives Host type
```
Each config file calls `defineHost()` and exports the resulting `HostConfig`
object, which tells the generator:
- Where to put generated skills (paths)
- How to transform frontmatter (allowlist/denylist fields)
- What Claude-specific references to rewrite (paths, tool names)
- What binary to detect for auto-install
- What resolver sections to suppress
- What assets to symlink at install time
The generator, setup script, platform-detect, uninstall, health checks, worktree
copy, and tests all read from these configs. None of them have per-host code.
## Step-by-step: add a new host
### 1. Create the config file
Configs are built with the `defineHost()` factory in `hosts/define-host.ts`.
You only write the fields that differ from the common external-host defaults;
everything else is derived from the host name. A fully-default host is two
fields (see `hosts/slate.ts` or `hosts/cursor.ts`):
```typescript
import { defineHost } from './define-host';
const myhost = defineHost({
name: 'myhost',
displayName: 'MyHost',
});
export default myhost;
```
That expands to the full `HostConfig` with these defaults:
- `cliCommand: 'myhost'` (the name; binary for `command -v` detection)
- `cliAliases: []`
- `globalRoot` / `localSkillRoot`: `.myhost/skills/gstack`, `hostSubdir`: `.myhost`
- `usesEnvVars: true` (false only for Claude, which uses literal `~` paths)
- `frontmatter`: allowlist keeping `name` + `description`, no description limit
- `generation`: no metadata file, `skipSkills: ['codex']` (codex skill is Claude-only)
- `pathRewrites`: the standard trio derived from the resolved paths
(`~/.claude/skills/gstack` → `~/{globalRoot}`, `.claude/skills/gstack`
`{localSkillRoot}`, `.claude/skills``{hostSubdir}/skills`)
- `suppressedResolvers`: the GBrain pair (`GBRAIN_CONTEXT_LOAD`, `GBRAIN_SAVE_RESULTS`)
- `runtimeRoot`: the shared asset list (`bin`, `browse/dist`, `browse/bin`,
`gstack-upgrade`, `ETHOS.md` + review checklist files)
- `install`: `{ linkingStrategy: 'symlink-generated' }`
- `learningsMode: 'basic'`
Override any field by passing it to `defineHost()`. Two path-rewrite options:
- `extraPathRewrites`: appends entries AFTER the derived trio (e.g. kiro's
codex-path cleanup, or `{ from: 'CLAUDE.md', to: 'AGENTS.md' }` for
AGENTS.md hosts). Use this when the standard trio is right but you need more.
- `pathRewrites`: replaces the derived list entirely. Only for non-mechanical
cases — codex and factory rewrite the global path to `$GSTACK_ROOT` and add
an extra review-path rewrite; claude has an empty list.
The two are mutually exclusive (the factory throws if you pass both).
Shared constants exported from `define-host.ts` for spread-composition:
`CROSS_MODEL_RESOLVERS` (the five Codex-invoking resolvers suppressed on
hosts that can't invoke other models), `GBRAIN_RESOLVERS` (the default
suppression pair), and `EXEC_STYLE_TOOL_REWRITES` (the OpenClaw-style
lowercase-tool rewrites shared by openclaw and gbrain).
Good examples: `hosts/opencode.ts` (path + runtimeRoot overrides),
`hosts/factory.ts` (tool rewrites and conditional fields), `hosts/hermes.ts`
(AGENTS.md host with custom tool rewrites and resolver composition).
### 2. Register in the index
Edit `hosts/index.ts`:
```typescript
import myhost from './myhost';
// Add to ALL_HOST_CONFIGS array:
export const ALL_HOST_CONFIGS: HostConfig[] = [
claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain, myhost
];
// Add to re-exports:
export { claude, codex, factory, kiro, opencode, slate, cursor, openclaw, hermes, gbrain, myhost };
```
### 3. Add to .gitignore
Add `.myhost/` to `.gitignore` (generated skill docs are gitignored).
### 4. Generate and verify
```bash
# Generate skill docs for the new host
bun run gen:skill-docs --host myhost
# Verify output exists and has no .claude/skills leakage
ls .myhost/skills/gstack-*/SKILL.md
grep -r ".claude/skills" .myhost/skills/ | head -5
# (should be empty)
# Generate for all hosts (includes the new one)
bun run gen:skill-docs --host all
# Health dashboard shows the new host
bun run skill:check
```
### 5. Run tests
```bash
bun test test/gen-skill-docs.test.ts
bun test test/host-config.test.ts
```
The parameterized smoke tests automatically pick up the new host. Zero test
code to write. They verify: output exists, no path leakage, valid frontmatter,
freshness check passes, codex skill excluded.
### 6. Update README.md
Add install instructions for the new host in the appropriate section.
## Config field reference
See `scripts/host-config.ts` for the full `HostConfig` interface with JSDoc
comments on every field.
Key fields:
| Field | Purpose |
|-------|---------|
| `frontmatter.mode` | `allowlist` (keep only listed) or `denylist` (strip listed) |
| `frontmatter.descriptionLimit` | Max chars, `null` for no limit |
| `frontmatter.descriptionLimitBehavior` | `error` (fail build), `truncate`, `warn` |
| `frontmatter.conditionalFields` | Add fields based on template values (e.g., sensitive → disable-model-invocation) |
| `frontmatter.renameFields` | Rename template fields (e.g., voice-triggers → triggers) |
| `pathRewrites` | Literal replaceAll on content. Order matters. Replaces the derived trio. |
| `extraPathRewrites` | (defineHost input only) Appended after the derived trio. |
| `toolRewrites` | Rewrite Claude tool names (e.g., "use the Bash tool" → "run this command") |
| `suppressedResolvers` | Resolver functions that return empty for this host |
| `coAuthorTrailer` | Git co-author string for commits |
| `boundaryInstruction` | Anti-prompt-injection warning for cross-model invocations |
## Validation
The `validateHostConfig()` function in `scripts/host-config.ts` checks:
- Name: lowercase alphanumeric with hyphens
- CLI command: alphanumeric with hyphens/underscores
- Paths: safe characters only (alphanumeric, `.`, `/`, `$`, `{}`, `~`, `-`, `_`)
- No duplicate names, hostSubdirs, or globalRoots across configs
Run `bun run scripts/host-config-export.ts validate` to check all configs.