feat: Factory Droid compatibility — works across Claude Code, Codex, and Factory (v0.13.5.0) (#621)

* refactor: extract processExternalHost() shared helper for multi-host generation

Refactor the Codex-specific output routing block in gen-skill-docs.ts into
a shared processExternalHost() function. Both Codex and future external hosts
(Factory Droid) will use this helper for output routing, symlink loop detection,
frontmatter transformation, path rewrites, and metadata generation.

- Rename codexSkillName() to externalSkillName() everywhere
- Extract ExternalHostConfig interface with per-host settings
- Codex output is byte-identical (verified via --dry-run)
- Skip /codex skill for all non-Claude hosts (not just codex)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add Factory Droid host type, preamble, and co-author trailer

- Add 'factory' to Host union type with .factory/skills/gstack paths
- Extend preamble runtime root detection for Factory ($HOME/.factory/)
- Add GSTACK_DESIGN env var to preamble (was missing for Codex too)
- Add Factory Droid co-author trailer for git commits

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: Factory Droid generation, --host all, and host-aware frontmatter

- Add --host factory (alias: --host droid) to gen-skill-docs
- Add --host all: generates for claude, codex, and factory in one invocation
  with fault-tolerant per-host error handling (only fails if claude fails)
- Factory frontmatter: name + description + user-invocable: true
- Factory sensitive skills: disable-model-invocation: true (from sensitive: field)
- Claude: strips sensitive: field from output (only Factory uses it)
- Factory tool name translation: Claude tool names → generic phrasing
- Replace chained gen:skill-docs calls with --host all in package.json build

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: sensitive frontmatter for Factory Droid auto-invocation safety

Add sensitive: true to 6 skill templates with side effects that Factory
Droids shouldn't auto-invoke (ship, land-and-deploy, guard, careful,
freeze, unfreeze). The field is:
- Factory: emitted as disable-model-invocation: true
- Claude/Codex: stripped from output by transformFrontmatter()

Also fix Claude host path: call transformFrontmatter() for Claude to
strip the sensitive: field from Claude output.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: gstack-platform-detect binary for multi-host debugging

Bash script that prints a table of installed AI coding agents (Claude,
Codex, Factory Droid, Kiro) with versions, skill paths, and gstack
installation status. Useful for debugging multi-host setups.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: Factory Droid support in setup script

- Add factory to --host values (auto-detected via command -v droid)
- Add .factory/ skill doc generation step alongside .agents/
- Add create_factory_runtime_root() and link_factory_skill_dirs()
  helpers mirroring the Codex equivalents
- Factory install section creates ~/.factory/skills/ with symlinks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: Factory Droid awareness in skill-check and uninstall

- skill-check.ts: add Factory skills validation and freshness check
- gstack-uninstall: add Factory artifact cleanup (~/.factory/skills/gstack*
  and per-project .factory/ sidecar)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: Factory Droid generation + --host all test suites

Add 13 new tests:
- Factory output paths, frontmatter (user-invocable, disable-model-invocation)
- Sensitive vs non-sensitive skill classification
- Path rewrites (no .claude/skills/ in Factory output)
- /codex skill exclusion, openai.yaml absence
- Factory keeps Codex integration blocks (for second opinions)
- --host droid alias, --dry-run freshness, preamble paths
- --host all generates for all 3 hosts
- Setup script host validation updated for factory

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: Factory Droid install instructions + CI freshness check

- README: add Factory Droid section with install instructions and
  restart note (Factory requires restart to rescan skills)
- CI: add Factory skill doc freshness verification to skill-docs.yml

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: generated Factory Droid skill output (.factory/skills/)

29 skills generated for Factory Droid with:
- user-invocable: true on all skills
- disable-model-invocation: true on 6 sensitive skills
- .factory/skills/ paths (no .claude/skills/ references)
- $GSTACK_ROOT env vars for runtime root detection
- Tool name translation (Claude tool names → generic phrasing)

Committed to git for CI freshness checks and direct consumption.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: add Factory Droid P1 TODO for browse MCP server

Add 3 TODOs under new ## Factory Droid section:
- P1: Browse MCP server (Option B, deeper Factory integration)
- P3: .agent/skills/ dual output for cross-agent compatibility
- P3: Custom Droid definitions alongside skills

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v0.13.5.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>