Support and audit the C# + Python repo shape (first case: PlexCleaner)

[ptr727]

Summary

PlexCleaner is now the fleet's first repo that is both C# and Python: a .NET console app plus a
self-contained, stdlib-only Python regression-tooling subtree under RegressionTests/ (ruff + mypy,
no runtime deps). See ptr727/PlexCleaner#855. This is a repo shape the template has never had to
audit, and I hit several cross-cutting decisions that aren't codified anywhere yet.

Because spec/project-types.json composes types as an array, a C#+Python repo does not need a
new type id — it is expressed as types: ["csharp", "console", "docker", "python"], and the audit
runs the union of the per-type checks. So the ask is not a new polyglot type; it is: (1)
register the shape, (2) codify how the csharp and python baselines coexist when stacked in one
repo, and (3) add a conformance-matrix row. I expect a few convergence iterations.

What the shape looks like (PlexCleaner)

• C# app at the root (types currently ["csharp","console","docker"]); should add "python".
• RegressionTests/ — a standalone Python subtree: 5 stdlib-only scripts + a Bash harness,
  pyproject.toml carrying only ruff + mypy config (no build/runtime metadata, no uv.lock).
• CI: a uvx-based ruff / ruff-format / mypy step in the existing validate workflow.
• No media/secrets; the subtree is utility tooling, not a shipped package and not test-covered code.

Cross-cutting decisions I had to make (candidates to codify)

1. Line endings. .editorconfig's C# governance is CRLF-by-default; Python has no [*.py]
   override, so .py inherits CRLF — matching Financial-Modeling's audited choice to keep Python on
   the repo default rather than pinning LF. Shebang-less scripts (invoked via python3/uvx) make
   CRLF safe. Worth stating explicitly for a mixed repo so nobody "fixes" .py to LF.
2. uvx-scripts vs uv-project. Financial-Modeling is a source-only python repo: uv project +
   uv.lock + prek. PlexCleaner's Python is a handful of stdlib-only scripts, so I used uvx with
   no lockfile and no uv project. The template needs a rule for when a Python subtree is
   "source-only python" (uv project, locked) vs "scripts embedded in another repo" (uvx, unlocked).
3. Tool-version pinning. I pin ruff/mypy only in CI (bumpable there) and run latest in the
   VSCode tasks / README examples, accepting a small visible local-vs-CI gap so local tooling never
   silently falls behind. Should this be the fleet default for uvx tooling?
4. Coverage. spec/files.json applies codecov.yml to ["csharp","python"], but this Python
   is lint/type-checked only — no pytest, no coverage. A mixed repo shouldn't be forced to add
   Python coverage for utility scripts; the python type's coverage expectation may need a
   "source-only" vs "scripts" distinction (overlaps with Template gaps found adapting to a source-only Python repo (Financial-Modeling) #306).
5. .vscode/tasks.json. files.json already has separate csharp and python references; a mixed
   repo must satisfy both. I added Ruff / Ruff-Format / Mypy tasks alongside the C# ones — please
   confirm the appliesTo union is the intended audit behavior here.
6. Docs. README ## Rules has ### If a C# Project / ### If a Python Project as alternatives;
   CODESTYLE.md has per-language sections. A repo that is both needs a "both apply" story.

Proposal

• Register PlexCleaner in registry/repos.json with types += "python".
• Codify the csharp+python coexistence rules above (line endings, uvx-vs-uv-project, CI-only pinning,
  coverage-optional for utility subtrees, tasks.json union) — in crossCutting and/or the README
  ## Rules.
• Add a csharp + python shape row to reports/conformance-matrix.md.

Related: #306 (Python source-only adaptation gaps), #310 (per-type cold-start self-test). Reference
implementation: ptr727/PlexCleaner#855.

[ptr727]

Fixed in #343 (merged to develop). The csharp+python shape is registered and its coexistence rules are codified, per three decisions settled up front:

1. Two python profiles, one type, split by whether the Python has third-party runtime dependencies (detected structurally from pyproject.toml, not by inspecting imports): PROJECT (PEP 621 uv project + committed LF-pinned uv.lock; Financial-Modeling) vs SCRIPTS (stdlib-only, uvx, no lock, pyproject tool-config-only; PlexCleaner RegressionTests/). New check python.profile.detect.
2. SCRIPTS tool-version pinning is CI-only (uvx ruff@X in CI, bumpable; latest in tasks/README) - the deliberate CI-vs-local gap #855 chose. New check python.scripts.uvx. PROJECT keeps pinning via uv.lock + --frozen.
3. Coverage N/A for SCRIPTS (no pytest); codecov.yml presence stays required by any co-present type with tests (the C# side). python.coverage.codecov carries the N/A wording.

Per-issue items: (1) line endings - CODESTYLE states .py follows the repo CRLF default; (2) uvx-vs-uv-project - python.profile.detect + CODESTYLE "Two profiles"; (3) CI-only pinning - python.scripts.uvx; (4) coverage - N/A wording; (5) tasks.json union - confirmed, no change needed (spec/files.json already carries both csharp+python references, satisfied by union); (6) docs both-apply - README "If Both C# and Python" + CODESTYLE "Two profiles".

Registered PlexCleaner types += python (+driftNote) and added the csharp+python row to reports/conformance-matrix.md (not-tested, pending #310's cold-start self-test). Two Copilot review rounds to a clean pass.