[FEATURE] Plugin-level skill composition command (`/compose`)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When I use Claude Code with complex workflows (e.g., implementing a feature),
I often need to apply multiple skills in sequence — such as TDD + code-review, or plan + security-review — but I have to invoke them one at a time.

When I'm writing new features, I find it difficult to keep both test discipline
and security awareness active simultaneously without manually switching between skills.

Proposed Solution

I'd like to be able to run /compose tdd security-review to activate both skills
simultaneously within a single session.

There should be a plugin (installable via the marketplace) that reads two skill definitions, merges their checklists and instructions, and injects them as a unified prompt context — without requiring any changes to the core TUI.

The interface should show a merged checklist from both skills, making it clear which items come from which skill.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Example scenario:

1. I'm implementing a new API endpoint in a Node.js backend
2. I want to follow TDD discipline AND catch security issues in real time
3. With this feature, I could run /compose tdd security-review at session start
4. Claude would enforce test-first workflow while simultaneously flagging

injection risks, missing input validation, and exposed secrets —
saving me a separate review pass after the fact

Additional Context

• Links to similar closed issues: #17349, #16759, #33121
• This requires no core TUI changes — implementable entirely as a channel plugin
• The plugin would read skill files from .claude/skills/ or the marketplace registry
• I'm interested in contributing this as a reference plugin implementation.

Would the maintainers be open to a PR for this? Happy to follow any
contribution guidelines.