Feature: marketplace-aware external skill recommendations in planning/design flows

[malikrohail]

Summary

gstack already suggests built-in workflow skills (/office-hours, /plan-eng-review, /plan-design-review, etc.), but it has no way to surface the best external skill when the user’s request clearly points to a specific technology ecosystem.

Examples:

• "Build a Next.js app on Vercel with Supabase auth"
• "Need Azure CLI guidance for deployment"
• "Need GitHub CLI workflow automation"
• "Use the official Supabase skill"

The external marketplace already supports search via the Agent Skills / skills.sh CLI:

• skills search <query>
• skills search <query> --json

That means gstack could do better inside planning/design flows by:

1. reading the original user request
2. extracting technology keywords
3. querying the marketplace
4. surfacing the top relevant external skills alongside gstack’s internal workflow suggestions

Related but distinct from #113:

• Make individual skills available via skills.sh #113 = publish gstack's own skills to skills.sh
• this issue = let gstack consume the marketplace to recommend third-party skills

Problem

Today gstack’s suggestion layer is static and in-repo. The root skill only suggests adjacent gstack stages (brainstorm -> /office-hours, architecture -> /plan-eng-review, etc.).

That works for workflow routing, but it misses a major opportunity:

• when the user mentions a vendor/platform/tool with a high-quality external skill already available
• when the best next step is not only another gstack skill, but also a specialized ecosystem skill
• when the user is in plan/design mode and would benefit from the best existing skill before implementation starts

Proposed behavior

Automatic recommendations in planning/design flows

When PROACTIVE=true, planning/design skills should automatically run marketplace lookup using a hybrid query:

• original user request
• extracted technology/framework keywords

Target skills:

• /office-hours
• /feature-scope
• /plan-ceo-review
• /plan-eng-review
• /plan-design-review
• /design-consultation
• /design-review
• /autoplan

The output should show the top 3 relevant external skills with:

• skill / repo name
• one-line why it matches
• install command

Manual parity path

Add a first-class manual command such as /find-skills <query> so users can explicitly do the same marketplace search on demand.

Safety / UX rules

• Recommendation-only for v1: never auto-install or auto-run third-party skills
• Respect PROACTIVE=false
• Gracefully degrade if the marketplace CLI is unavailable
• Pass raw user text through a temp file or safe argument path, not shell interpolation
• Suppress obvious duplicates when gstack already has a strong built-in answer

Implementation sketch

1. Add a helper script (for example bin/gstack-marketplace-search) that:

   • accepts a query file / query string
   • extracts normalized tech keywords
   • calls skills search <query> --json
   • falls back to npx -y agent-skills-cli search <query> --json if needed
   • normalizes and ranks results
   • caches results in ~/.gstack/cache/

2. Add a shared template resolver in scripts/gen-skill-docs.ts that injects marketplace lookup instructions into planning/design skills.

3. Add a manual /find-skills skill that uses the same helper.

4. Update docs / validation / host generation so the new capability works for both Claude and Codex output.

Acceptance criteria

• gstack can query the marketplace and normalize results
• planning/design skills surface relevant external skills automatically when appropriate
• /find-skills <query> exists for manual parity
• recommendations are suggestion-only, never auto-install
• feature is configurable and respects PROACTIVE
• tests cover CLI fallback, ranking, prompt integration, and docs/host generation