docs: local dev runner (dev.py) + README install/dev sections

README.md

@@ -37,3 +37,26 @@ print(resp)
 
 You can also retrieve the value directly with `fp.client.get_fingerprint()` if
 you prefer to handle network communication yourself.
+
+## Installation
+
+```bash
+pip install fp-py            # from a checkout: pip install .
+```
+
+`fp-py` has **zero runtime dependencies** — it imports only the Python standard
+library. This is declared in `pyproject.toml` (`dependencies = []`) and enforced
+in CI by `tools/dep_guard.py`.
+
+## Development
+
+Run the full dev loop locally — no external services, no paid tooling:
+
+```bash
+python -m pip install -e ".[dev]"   # one-time (adds coverage, dev-only)
+python dev.py check                 # zero-dependency guard + unittest suite
+python dev.py cov                   # tests + coverage report
+```
+
+`dev.py` is a stdlib-only runner (`python dev.py {check,test,cov,guard}`). CI runs
+the same `unittest` suite across Python 3.9–3.13 plus the dependency guard.

dev.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Local dev runner for fp-py — stdlib only, no third-party task runner.
+
+Run the tight dev loop on your own machine (free) instead of via paid agents:
+
+  python -m pip install -e ".[dev]"   # one-time setup
+  python dev.py check                 # guard + tests (what CI runs)
+  python dev.py test                  # unittest suite
+  python dev.py cov                   # tests + coverage report
+  python dev.py guard                 # zero-dependency guard
+"""
+from __future__ import annotations
+
+import subprocess
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent
+PY = sys.executable
+
+
+def run(*args: str) -> int:
+    print(f"$ {' '.join(args)}")
+    return subprocess.call(args, cwd=str(ROOT))
+
+
+def test() -> int:
+    return run(PY, "-m", "unittest", "discover", "-s", "tests", "-t", ".")
+
+
+def cov() -> int:
+    rc = run(PY, "-m", "coverage", "run", "--source=fp",
+             "-m", "unittest", "discover", "-s", "tests", "-t", ".")
+    return rc or run(PY, "-m", "coverage", "report", "-m")
+
+
+def guard() -> int:
+    return run(PY, "tools/dep_guard.py")
+
+
+def check() -> int:
+    return guard() or test()
+
+
+COMMANDS = {"test": test, "cov": cov, "guard": guard, "check": check}
+
+
+def main(argv: list[str]) -> int:
+    cmd = argv[1] if len(argv) > 1 else "check"
+    fn = COMMANDS.get(cmd)
+    if fn is None:
+        print(f"unknown command {cmd!r}; choose from: {', '.join(COMMANDS)}")
+        return 2
+    return fn()
+
+
+if __name__ == "__main__":
+    raise SystemExit(main(sys.argv))