# L4 — verify-blast-radius-not-just-defect
id: L4 · group: - · status: active · tags: legacy,memory · origin: legacy memory verify-blast-radius-not-just-defect.md · added: 2026-09-29

**Verify the BLAST RADIUS, not just the DEFECT.** (Phase 26, 2026-07-14 — I got this wrong in front of Drew.)

A coverage audit reported that `progress.py` under-counted ~243k instructions because `classify()` reads a K&R
definition as a forward declaration. I did the R14 thing — reproduced the mechanism against the bytes, confirmed
it was real, measured 400 banked instances in that shape — and then told Drew our headline numbers had been
under-reporting our progress.

**Wrong.** The headline metrics come from `weighted_metrics()`, which never calls `classify()` at all: it tests
"is this function still an `INCLUDE_ASM` stub?", so it is structurally immune to the bug. The published
instruction-weighted and distinct-code numbers were correct all along; only a secondary function-count report was
wrong.

**Why:** *"this tool is broken"* and *"this number is wrong"* are different claims requiring different evidence.
A confirmed mechanism proves nothing about consequence. Before reporting impact, trace the defect to the actual
consumer and check whether that consumer is even on the affected path.

**How to apply:**
- After confirming a defect, ask *"who consumes this, and does the consumer use this code path?"* — then verify
  THAT, not the defect, before quoting an impact number to the owner.
- **A null result where you predicted a large effect is a refutation — chase it, do not wave it off.** The fix
  moved the numbers by +376 instructions when I had predicted +190,000. That gap was the whole story and it
  would have been trivially easy to dismiss as noise (or worse, to report as "the fix worked, the numbers moved").
- Do not amplify a sub-agent's impact claim (R14) — the auditor conflated "classify() is blind" with "the metrics
  are wrong", and I propagated it as fact while lecturing about unverified oracles.

Related: [[derive-from-invariants-not-reparsing]].