feat(workflows): add plugin slots

[markuswondrak]

Summary

Adds the upstream opt-in plugin workflow slot described in Discussion #3473, building on the standalone WorkflowResolver introduced by #3557.

• Registers a stateless plugin step that persists an unfilled named slot as skipped with output.slot.
• Allows project overlays to fill slots through the existing ID-anchored replace operation, without changing resolver or merge semantics.
• Rejects slots inside fan-out.step templates because runtime-multiplied templates are not addressable overlay anchors.
• Adds engine, resolver-attribution, bundled-reference, documentation, and manual testing-guide coverage.

Validation

• .venv/bin/python -m pytest tests/workflows/ tests/test_workflows.py -v
• .venv/bin/python -m pytest tests/unit/test_bundler_references.py -v
• .venv/bin/python -m pytest tests/test_presets.py -v
• Manual disposable-project smoke: unfilled state, overlay replacement, persisted state, and resolver attribution.

Scope

No new CLI verbs, PresetResolver changes, shared helper extraction, resolver/merge behavior changes, bundled workflow slot, or status-color change.

Posted on behalf of @markuswondrak by GitHub Copilot (model: gpt-5.6-terra, autonomous).

[Copilot]

Pull request overview

Adds opt-in plugin slots to workflows, enabling project overlays to replace upstream extension points safely.

Changes:

• Registers and validates the stateless plugin step.
• Persists unfilled slots as skipped and rejects fan-out placement.
• Adds automated tests and user documentation.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/specify_cli/workflows/__init__.py	Registers the plugin step.
src/specify_cli/workflows/engine.py	Validates plugin types and fan-out restrictions.
src/specify_cli/workflows/steps/plugin/__init__.py	Implements plugin-slot behavior.
tests/workflows/test_plugin_step.py	Tests validation, execution, overlays, and attribution.
tests/unit/test_bundler_references.py	Covers bundled plugin references.
tests/test_workflows.py	Updates built-in registry expectations.
docs/reference/workflows.md	Documents plugin-slot usage.
workflows/README.md	Adds the plugin step overview.
workflows/PUBLISHING.md	Adds plugin to publishing validation.
workflows/ARCHITECTURE.md	Updates workflow architecture documentation.
spec/workflow_overlays/OVERLAY_TESTING_GUIDE.md	Adds a manual validation walkthrough.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.