Add AGENTS.md

Author: john-kurkowski

AGENTS.md

@@ -0,0 +1,21 @@
+# Repository Guidance
+
+See [README.md](README.md) for contributor setup.
+
+## Tests
+
+Before wrapping up a change, run the relevant validation commands from the
+README:
+
+```zsh
+tox --parallel       # Test all Python versions
+tox -e py310         # Test specific Python version
+ruff format .        # Format code
+```
+
+Prefer the minimum Python version while iterating, `tox -e py310`. Then use
+broader validation when the scope of the change warrants it.
+
+Most `tox` environments forward to `pytest`. To focus one environment's tests,
+use a `pytest` selector such as `tox -e py310 -- -k private`, or run a specific
+test file such as `tox -e py310 -- tests/cli_test.py`.

CLAUDE.md

@@ -0,0 +1 @@
+AGENTS.md

README.md

@@ -196,7 +196,7 @@ See [URL validation](#url-validation) and
 
 ```zsh
 tox --parallel       # Test all Python versions
-tox -e py311         # Test specific Python version
+tox -e py310         # Test specific Python version
 ruff format .        # Format code
 ```