Chore: Pin ruff rule selection

[ModeSevenIndustrialSolutions]

Why

This repo runs the ruff hook with no ruff configuration, so it applies whatever ruff's default rule set happens to be. That default is not stable across releases — verified directly:

$ ruff 0.15.22 check --show-settings --isolated
 59 rules across  2 categories (E, F)

$ ruff 0.16.0 check --show-settings --isolated
413 rules across 38 categories

A 7× expansion in a patch-level bump. The routine autoupdate that crossed it broke 15 repos in this org simultaneously on untouched code — including this one, where #133 is blocked on 6 violations.

What

[lint]
select = ["E", "W", "F", "I", "B", "C4", "UP"]
ignore = ["E501", "B008"]

Not invented — this is the de facto house style, a superset in 13 of the 16 org repos that already pin their rules.

A standalone .ruff.toml because this repo has no pyproject.toml.

Selecting these categories switches every other rule off — that is the point. Adopting them becomes a deliberate, reviewed change rather than a side effect of a version bump.

line-length and target-version are left unset on purpose — both would change behaviour rather than pin it (target-version alters which pyupgrade rules fire). Standardising those is separate work.

Effect on #133

All 6 blocking violations fall outside the pinned set and cease to exist:

Rule	Count	In core-7?
EXE001	2	No — EXE not selected
BLE001	1	No — BLE not selected
PIE810	1	No — PIE not selected
SIM103	1	No — SIM not selected
SIM115	1	No — SIM not selected

Two of those (BLE001 on a tomllib.load wrapper, SIM115 on the conditional emit() file handle) were the ones needing a judgement call, where the existing code is not actually wrong. This removes the need to contort them.

Validation

• No code changes needed — verified clean under the pinned set with ruff 0.16.0 against the files the hook selects
• ruff check --show-settings confirms enabled categories drop from 38 to B C E F I UP W
• pre-commit run --all-files → all hooks pass

[Copilot]

Pull request overview

Adds an explicit Ruff configuration to stabilize the lint rule set across Ruff releases, avoiding unexpected rule expansions from ruff default selections when pre-commit autoupdates change the Ruff version.

Changes:

• Introduces a standalone .ruff.toml with an explicit [lint] select list (E/W/F/I/B/C4/UP) and a small global ignore set (E501, B008).
• Adds tests/**/*.py per-file ignores to prevent future widening of select from immediately flagging test modules.

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[tykeal]

🤖 Dependamerge
Approved this pull request ✅

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

.ruff.toml:17

• The sentence "Pinning does not decline the unselected rules" reads like a typo/word-choice error and is unclear about the intent (pinning is about controlling which rules run by default, not “declining” rules). Consider rephrasing to make the point explicit.

# Pinning does not decline the unselected rules.  It makes adopting them
# a deliberate, reviewed change instead of a side effect of a version