initial: add all custom Claude.ai skills

my-python-senior/systems.md

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+# Systems Python Guidelines
+
+## CLI tools and system utilities
+
+- Prefer `argparse` or `typer` for CLIs, not ad-hoc `sys.argv` parsing.
+- Always provide:
+  - `--help` with clear descriptions
+  - examples in docstrings or README
+  - reasonable defaults and safe behavior.
+- For non-trivial tools, separate:
+  - CLI entrypoint (`main()` or Typer app)
+  - core logic in importable modules (no side effects on import).
+
+## Logging and diagnostics
+
+- Use the `logging` module instead of `print` for diagnostics.
+- Provide configurable log levels; default to `INFO` for CLI tools.
+- For structured logging, prefer JSON-compatible formats when integrating with centralized logging.
+- Avoid logging secrets, access tokens, and PII.
+
+## Configuration
+
+- Prefer explicit configuration (CLI args, env vars, config files) over hidden magic.
+- Use `pydantic` or `dataclasses` for structured config when appropriate.
+- For multi-environment setups, support:
+  - baseline config
+  - overrides via env or separate files.
+
+## Packaging and layout
+
+- Use modern packaging (`pyproject.toml` with `setuptools`/`hatch`/`poetry`).
+- Standard layout:
+  - `src/<package_name>/...`
+  - `tests/`
+  - minimal, well-documented dependencies.
+- For tools that may be reused, publishable or installable layout is preferred even in internal projects.
+
+## Error handling
+
+- Fail fast on invalid configuration or obvious misuse.
+- Wrap external calls (filesystem, network, subprocesses) with clear error messages.
+- Use custom exception types where it improves clarity.
+- Never silently swallow exceptions; at minimum, log with context.