Add instructions for Codex

Author: zah

AGENTS.md

@@ -0,0 +1,36 @@
+# Instructions for Codex
+
+To run the test suite, execute:
+
+```
+make test
+```
+
+The tester executes a number of sample programs in `tests/programs` and compares their outputs to the fixtures in `tests/fixtures`.
+
+# Code quality guidelines
+
+- Strive to achieve high code quality.
+- Write secure code.
+- Make sure the code is well tested and edge cases are covered. Design the code for testability.
+- Write defensive code and make sure all potential errors are handled.
+- Strive to write highly reusable code with routines that have high fan in and low fan out.
+- Keep the code DRY.
+- Aim for low coupling and high cohesion. Encapsulate and hide implementation details.
+
+# Code commenting guidelines
+
+- Document public APIs and complex modules.
+- Maintain the comments together with the code to keep them meaningful and current.
+- Comment intention and rationale, not obvious facts. Write self-documenting code.
+- When implementing specific formats, standards or other specifications, make sure to
+  link to the relevant spec URLs.
+
+# Writing git commit messages
+
+The first line of the commit message should follow the "conventional commits" style:
+https://www.conventionalcommits.org/en/v1.0.0/
+
+In the remaining lines, provide a short description of the implemented functionality.
+Provide sufficient details for the justification of each design decision if multiple
+approaches were considered.