New closure instances of functions like parse-loop get l_compiled=None even though a previous instance already failed. Now check _jit_warned by name and immediately sentinel-mark new instances of known failures. The first failure is always logged. Subsequent instances are silently sentinel-marked — no recompilation, no log spam, no suppressed errors. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>