plugins/mattstack: README lists process-digraphs; certify plugin/skills in CI

[m4ttheweric]

Follow-up to #544: the README now lists process-digraphs as public, and CI certifies the skills under plugin/skills/, which its certify loop never reached before.

What changed

• The README's "What's inside" list adds mattstack:process-digraphs, and the Infra section gets a bullet for it
• The plugin-mattstack certify loop now also walks plugin/skills/*/
• plugin.json goes to 0.27.5 (RT-355, RT-357: herd watchdog follow-up rounds and form-only gate Escape #543 takes 0.27.4)

Verification

• The five plugin/skills dirs were never certified by CI; each passes sh tests/certify.sh (exit 0), so no skill needed a fix.
• The full new loop (skills/*/ plugin/skills/*/ attachments/*/ attachments/*/*/) runs locally with no failures.
• scripts/repo-purity.sh passes.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added mattstack:process-digraphs for creating or revising process workflows as diagrams, with support for rendering and linting.
• Documentation
  • Updated the list of directly invocable skills to include process diagram workflows.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 5b2f8298-78a2-40ce-b4e0-f2d87cbdd17d

📥 Commits

Reviewing files that changed from the base of the PR and between a24b734 and d3fb1f8.

📒 Files selected for processing (3)

• .github/workflows/checks.yml
• plugins/mattstack/.claude-plugin/plugin.json
• plugins/mattstack/README.md

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📝 Walkthrough

Walkthrough

The README documents mattstack:process-digraphs and its tools. The certification loop now searches plugin skill directories, and the plugin version changes to 0.27.5.

Changes

Process digraph skill registration

Layer / File(s)	Summary
Document and certify the process-digraphs skill .github/workflows/checks.yml, plugins/mattstack/README.md, plugins/mattstack/.claude-plugin/plugin.json	The README lists and describes the skill. The certification loop searches plugin/skills/*/, and the plugin version changes to 0.27.5.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to d3fb1

The documentation, skill certification paths, and plugin version update appear consistent. No material merge risk is evident.

Architecture Summary

Architecture risk: 🔵 Low · up to d3fb1

The change affects 1 system.

Changed systems: plugins

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — plugins (service) was modified; 2 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in plugins/mattstack/.claude-plugin/plugin.json: The plugin metadata version changes from 0.27.3 to 0.27.5.
• observed — Modified behavior in plugins/mattstack/README.md: The directly invocable skill list now names mattstack:process-digraphs; the surrounding description of other skills as engines remains.
• observed — Modified behavior in plugins/mattstack/README.md: The Infra section adds mattstack:process-digraphs, describing the digraph format and its rendering and linting tools.
• observed — Modified behavior in .github/workflows/checks.yml: The certification loop now includes plugin/skills/*/ in its directory search; all existing search paths remain.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the README update and CI certification-loop change, which are the main changes in the pull request.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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