# Diagnostic stderr writes [XYZ_DIAG] in src/*.py are technical debt; use tests/artifacts/<name>.diag.log or /tmp/diag_*.py

From `conductor/code_styleguides/python.md` §8 "AI-Agent Specific Conventions":
- **No diagnostic noise in production code (Added 2026-06-09).** `sys.stderr.write(f"[XYZ_DIAG] ...")` lines added to `src/*.py` for one-time debugging are technical debt the moment they ship. The project's production code should not contain `[XYZ_DIAG]` markers, `print(...debug...)` calls, or any other ad-hoc debug instrumentation. The right place for diagnostic output during a one-time investigation is `tests/artifacts/<test_name>.diag.log` (a log file) or a standalone `/tmp/diag_<name>.py` script. If you must instrument a production function for a single test run, the diag lines are part of the same atomic commit as the fix — they do not live uncommitted in the working tree. If you "revert everything," that means the diag lines are also reverted.

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From `AGENTS.md` "No Diagnostic Noise in Production (kill it)":
- Diagnostic stderr goes to a log file (`tests/artifacts/<test_name>.diag.log`) or to a temporary diagnostic script (`/tmp/diag_rag.py`), NOT to `src/*.py`. If you absolutely must instrument a production function for a single test run, the diag lines are part of the same atomic commit as the fix — they do not live uncommitted in the working tree. If you "revert everything," that means the diag lines are also reverted.