Add standardized linting workflow and config

.github/workflows/format.yml

@@ -1,23 +1,61 @@
-name: pre-commit-format
+name: pre-commit (PR only on changed files)
 
 on:
-  push:
-    branches: [main]
   pull_request:
-    branches: [main]
+    types: [opened, synchronize, reopened]
 
 jobs:
-  pre_commit_checks:
+  detect_changes:
     runs-on: ubuntu-latest
+    outputs:
+      changed: ${{ steps.changed_files.outputs.changed }}
+
     steps:
-      - uses: actions/checkout@v3
+      - name: Checkout full history
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Detect changed files
+        id: changed_files
+        run: |
+          git fetch origin ${{ github.base_ref }}
+          CHANGED_FILES=$(git diff --name-only origin/${{ github.base_ref }}...HEAD)
+
+          {
+            echo "changed<<EOF"
+            echo "$CHANGED_FILES"
+            echo "EOF"
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Show changed files
+        run: |
+          echo "Changed files:"
+          echo "${{ steps.changed_files.outputs.changed }}"
+
+  precommit:
+    needs: detect_changes
+    runs-on: ubuntu-latest
+    if: ${{ needs.detect_changes.outputs.changed != '' }}
+
+    steps:
+      - name: Checkout PR branch
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
           ref: ${{ github.head_ref }}
 
-      - uses: actions/setup-python@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: "3.12"
+
+      - name: Install pre-commit
+        run: pip install pre-commit
 
-      - run: pip install pre-commit
-      - run: pre-commit run --all-files
+      - name: Run pre-commit (CI check-only stage) on changed files
+        env:
+          CHANGED_FILES: ${{ needs.detect_changes.outputs.changed }}
+        run: |
+          mapfile -t files <<< "$CHANGED_FILES"
+          pre-commit run --hook-stage manual --files "${files[@]}" --show-diff-on-failure

.pre-commit-config.yaml

@@ -1,28 +1,61 @@
+default_stages: [pre-commit]
+
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v6.0.0
     hooks:
+      # These are safe to run in both local & CI (they don't require "fix vs check" split)
       - id: check-added-large-files
+        stages: [pre-commit, manual]
       - id: check-yaml
+        stages: [pre-commit, manual]
       - id: check-toml
+        stages: [pre-commit, manual]
+      - id: check-merge-conflict
+        stages: [pre-commit, manual]
+
+      # These modify files. Run locally only (pre-commit stage).
       - id: end-of-file-fixer
-      - id: name-tests-test
-        args: [--pytest-test-first]
+        stages: [pre-commit]
       - id: trailing-whitespace
-      - id: check-merge-conflict
+        stages: [pre-commit]
+
   - repo: https://github.com/tox-dev/pyproject-fmt
     rev: v2.15.2
     hooks:
       - id: pyproject-fmt
+        stages: [pre-commit]    # modifies -> local only
+
   - repo: https://github.com/abravalheri/validate-pyproject
     rev: v0.25
     hooks:
       - id: validate-pyproject
+        stages: [pre-commit, manual]
+
   - repo: https://github.com/astral-sh/ruff-pre-commit
     rev: v0.15.0
     hooks:
-      # Run the formatter.
+      # --------------------------
+      # LOCAL AUTOFIX (developers)
+      # --------------------------
+      - id: ruff-check
+        name: ruff-check (fix)
+        args: [--fix, --unsafe-fixes]
+        stages: [pre-commit]
+
       - id: ruff-format
-      # Run the linter.
+        name: ruff-format (write)
+        stages: [pre-commit]
+
+      # --------------------------
+      # CI CHECK-ONLY (no writes)
+      # --------------------------
       - id: ruff-check
-        args: [--fix,--unsafe-fixes]
+        name: ruff-check (ci)
+        args: [--output-format=github]
+        stages: [manual]
+
+      - id: ruff-format
+        name: ruff-format (ci)
+        args: [--check, --diff]
+        stages: [manual]