Replace black formatter references with ruff (#109)

* Replace black formatter references with ruff in skills and commands

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Replace remaining black formatter references with ruff format

Update agent docs (pr-pusher, rules-engineer, ci-fixer) and
policyengine-core-skill to use ruff format instead of black.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Add changelog fragment

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: MaxGhenis

agents/country-models/ci-fixer.md

@@ -243,16 +243,16 @@ policyengine-core test policyengine_us/tests/policy/baseline/gov/states/ar/dhs/t
 
 #### Linting/Formatting
 ```bash
-# CRITICAL: Use uv run to ensure correct black version from uv.lock
+# CRITICAL: Use uv run to ensure correct ruff version from uv.lock
 # This matches CI exactly
 uv sync --extra dev
-uv run black . -l 79
+uv run ruff format
 
-# DO NOT use bare 'black' command - may use wrong version!
+# DO NOT use bare 'ruff' command - may use wrong version!
 
 # Commit formatting fixes
 git add -A
-git commit -m "Fix: Apply black formatting"
+git commit -m "Fix: Apply ruff formatting"
 git push
 ```
 
@@ -513,7 +513,7 @@ gh pr edit --add-reviewer @reviewer-username
 
 ## Common CI Issues and Fixes
 
-### 1. Black Formatting
+### 1. Ruff Formatting
 **Error**: `would reformat file.py`
 **Fix**: Run `make format` and commit
 

agents/country-models/pr-pusher.md

@@ -43,7 +43,7 @@ This ensures you have the complete patterns and standards loaded for reference t
 ## CRITICAL: Version Sync
 
 **Always use `uv run` for Python tools to ensure versions match CI:**
-- `uv run black . -l 79` - NOT `black . -l 79`
+- `uv run ruff format` - NOT `ruff format`
 - `uv run isort .` - NOT `isort .`
 - `uv run pytest` - NOT `pytest`
 
@@ -76,14 +76,14 @@ python -c "import yaml; yaml.safe_load(open('changelog_entry.yaml'))" || exit 1
 ### Step 2: Run Formatters
 
 ```bash
-# CRITICAL: Use uv to ensure correct black version from uv.lock
+# CRITICAL: Use uv to ensure correct ruff version from uv.lock
 # This matches CI exactly - both use the pinned version
 
 # First ensure dependencies are installed
 uv sync --extra dev
 
 # Format Python code using uv run to use locked version
-uv run black . -l 79
+uv run ruff format
 
 # Also run linecheck if available
 uv run linecheck . --fix 2>/dev/null || true
@@ -96,7 +96,7 @@ git add -A
 if ! git diff --cached --quiet; then
   git commit -m "Apply code formatting
 
-- Run black with 79 char line length (from uv.lock)
+- Run ruff format (from uv.lock)
 - Fix import ordering
 - Apply standard formatting rules"
 fi
@@ -117,7 +117,7 @@ if grep -q "error:" lint_output.txt; then
   autoflake --remove-all-unused-imports --in-place --recursive .
 
   # Fix import order
-  isort . --profile black --line-length 79
+  isort . --profile ruff --line-length 79
 
   # Commit fixes
   git add -A
@@ -182,7 +182,7 @@ $DESCRIPTION
 
 ## Checklist
 - [ ] Changelog entry added
-- [ ] Code formatted with black
+- [ ] Code formatted with ruff format
 - [ ] Linting passes
 - [ ] Tests pass locally
 - [ ] CI checks pass
@@ -234,18 +234,18 @@ fi
 
 ```bash
 # Fix with isort
-isort . --profile black --line-length 79
+isort . --profile ruff --line-length 79
 ```
 
-### Black Formatting
+### Ruff Formatting
 
 ```bash
-# CRITICAL: Use uv run to ensure correct black version from uv.lock
+# CRITICAL: Use uv run to ensure correct ruff version from uv.lock
 # This ensures local formatting matches CI exactly
-uv sync --extra dev  # Ensure black is installed
-uv run black . -l 79
+uv sync --extra dev  # Ensure ruff is installed
+uv run ruff format
 
-# DO NOT use bare 'black' command - it may use wrong version!
+# DO NOT use bare 'ruff' command - it may use wrong version!
 ```
 
 ### Unused Imports

agents/country-models/rules-engineer.md

@@ -533,8 +533,8 @@ Run through the skill's Quick Checklist before finalizing.
 # CRITICAL: Use uv run to ensure correct tool versions from uv.lock
 uv sync --extra dev  # Ensure all dev dependencies installed
 
-# Format code using locked black version
-uv run black . -l 79
+# Format code using locked ruff version
+uv run ruff format
 
 # Run tests to verify implementation
 uv run pytest policyengine_us/tests/policy/baseline/gov/states/STATE/ -v --maxfail=5

changelog.d/update-ruff-references.changed.md

@@ -0,0 +1 @@
+Update skill and agent references from black to ruff format.

commands/encode-reform.md

@@ -339,7 +339,7 @@ Validate the reform implementation. Check this reform-specific checklist:
 Also check standard code quality:
 - Parameter metadata complete (unit, period, label, reference)
 - Variable patterns correct (adds vs add(), entity levels)
-- Code style (black formatting, import ordering)
+- Code style (ruff formatting, import ordering)
 - Reference format (title with full section, href with #page=XX)
 
 Write {PREFIX}-checkpoint.md (≤15 lines):

skills/documentation/policyengine-standards-skill/SKILL.md

@@ -2,7 +2,7 @@
 name: policyengine-standards
 description: |
   PolicyEngine coding standards, formatters, CI requirements, and development best practices.
-  Triggers: "CI failing", "linting", "formatting", "before committing", "PR standards", "code style", "black formatter", "prettier", "pre-commit"
+  Triggers: "CI failing", "linting", "formatting", "before committing", "PR standards", "code style", "ruff formatter", "prettier", "pre-commit"
 ---
 
 # PolicyEngine Standards Skill
@@ -152,16 +152,16 @@ bun test -- --watch          # Watch mode
 ## Python Standards
 
 ### Formatting
-- **Formatter**: Black with 79-character line length
-- **Command**: `make format` or `black . -l 79`
-- **Check without changes**: `black . -l 79 --check`
+- **Formatter**: Ruff
+- **Command**: `make format` or `ruff format .`
+- **Check without changes**: `ruff format --check .`
 
 ```bash
 # Format all Python files
 make format
 
 # Check if formatting is needed (CI-style)
-black . -l 79 --check
+ruff format --check .
 ```
 
 ### Code Style
@@ -350,7 +350,7 @@ If the renamed repo is embedded in another site (e.g., via iframe or GitHub Page
 ## Resources
 
 - **Main CLAUDE.md**: `/PolicyEngine/CLAUDE.md`
-- **Python Style**: PEP 8, Black documentation
+- **Python Style**: PEP 8, Ruff documentation
 - **React Style**: Airbnb React/JSX Style Guide
 - **Testing**: pytest documentation, Jest/RTL documentation
 - **Writing Style**: See policyengine-writing-skill for blog posts, PR descriptions, and documentation

skills/tools-and-apis/policyengine-core-skill/SKILL.md

@@ -527,6 +527,6 @@ sim.calculate("variable", period)
 
 **Development standards:**
 - Python 3.10-3.13
-- Black formatting (79-char)
+- Ruff formatting (79-char)
 - Comprehensive tests
 - No breaking changes without discussion