Checkpoint
One last thing before we move on. Same surface as a write step — but the lesson doesn't complete until this passes.
Assemble the triage core: group the scored rows by segment, print each segment's full matrix line f"{g:<8} TP={tp} FP={fp} FN={fn} TN={tn} (n={len(rows)})" (segments alphabetical), then find the segment with the MOST misses and print f"most misses: {seg}" followed by one " missed: score=... label=..." line per missed row — stage 3's read-the-failures habit, mechanized.