Backend Feature Development

Use this skill for Python backend changes.

Workflow

1. Read AGENTS.md before coding.
2. Read the required specs listed in AGENTS.md for the affected protocol or feature area.
3. Read scoped AGENTS files for touched subtrees, such as src/merchant/AGENTS.md, src/apps_sdk/AGENTS.md, or src/agents/AGENTS.md.
4. Implement minimal, spec-aligned changes.
5. Add or update tests for new behavior, edge cases, and failure paths.
6. Run the relevant quality gates and report exact evidence.

Python Standards

• Use type hints for public APIs and non-trivial logic.
• Prefer explicit, readable code over clever abstractions.
• Avoid side effects at import time.
• Mock external services and I/O in tests.
• Do not add secrets, credentials, or sensitive data.
• Add comments only where they clarify non-obvious behavior.

CI Parity

Run these commands from the repo root before committing backend-related changes:

uv run ruff check src/merchant/ src/payment/ src/apps_sdk/ tests/
uv run ruff format --check src/merchant/ src/payment/ src/apps_sdk/ tests/
uv run pyright src/merchant/ src/payment/ src/apps_sdk/
uv run pytest tests/ -v --tb=short

Rules:

• Do not commit if any required command fails.
• If changes touch both backend and UI, run the UI CI parity commands in skills/ui/SKILL.md.
• Targeted tests are fine while iterating, but full relevant checks are required before commit unless explicitly skipped with a reason.

Testing Standards

• Name tests test_*.py.
• Assert behavior, not implementation details.
• Prefer fixtures over ad hoc setup/teardown logic.
• Use parametrized tests for related cases.
• Cover happy paths, edge cases, and failure paths when behavior changes.

Review Expectations

• No commented-out code.
• No TODOs without an issue reference.
• No dead code.
• No ignored warnings or silenced type errors unless justified.
• Clear, descriptive function and variable names.

The work is incomplete if tests are missing for changed behavior, Ruff or type checks are unresolved, or code behavior conflicts with the required docs.