style: format the code base with ruff and check it in CI

.git-blame-ignore-revs

@@ -0,0 +1,5 @@
+# Commits that only reformat code; git blame skips them.
+# Enable locally with: git config blame.ignoreRevsFile .git-blame-ignore-revs
+
+# style: format the code base with ruff
+99b337fe5f238f6d9244f4c6431f7070628de1d5

.github/workflows/Build.yml

@@ -3,6 +3,20 @@ name: CI
 on: [push, workflow_call]
 
 jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v7
+
+      - name: Check formatting with ruff
+        run: uv run --locked --only-group lint ruff format --check .
+
+      - name: Check for obvious errors with ruff
+        run: uv run --locked --only-group lint ruff check .
+
   build:
     runs-on: ubuntu-latest
     strategy:

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## [Unreleased]
 
+### Changed
+- The whole code base is formatted with `ruff format` (line length 88). The change is purely cosmetic: the syntax tree of every file is unchanged, apart from whitespace inside docstrings, and the Python examples of `hypyp/sync/README.md` are formatted too. The vendored `hypyp/ext` and the tutorial notebooks are left untouched. The formatting commit is listed in `.git-blame-ignore-revs`, so `git blame` skips it (run `git config blame.ignoreRevsFile .git-blame-ignore-revs` once in your clone; GitHub applies it automatically)
+- The CI now checks formatting (`ruff format --check`) and a small set of lint rules that only catch certain bugs: syntax errors, invalid comparisons and undefined names. Ruff comes from the new `lint` dependency group, which the `dev` group includes
+- `black` is removed from the `dev` dependency group, since `ruff format` replaces it
+
 ## [0.6.1] - 2026-10-03
 
 ### Fixed