RECURSIVE leg census over research/, tracked files only
  dirs holding *.jsonl          : 177
  dirs holding *.jsonl or *.log : 321
  *.jsonl files                 : 709
  *.log files                   : 1818
  committed *.py under research/: 1078

ARITHMETIC-SHAPE grep for the two-line-crossing construction (the 18 Sep lane's lesson):
harness/nttfwsum.py
an internal note
rounds/w3win-nibble-2026-09-18/w3winred.py
rounds/wask-nibble-2026-09-16/waskred.py