Hardcase stress harness: seeded corruption + misplacement curves

structure-stress.ts measures what survives typos, OCR-class character
confusions, whitespace damage, and swapped 3-line blocks - seeded and
deterministic, scored self-relative against the clean parse. LAB
credit agreement: 92.4% label / 98.1% anchor recall at 0.5% per-char
corruption, 75.0%/85.6% at 2%, 78.9%/91.3% in the combined worst case,
with ladder restarts/violations rising as designed disorder signals.
CBCA statute run exposes two honest findings recorded for the sweep:
the statute plane has clean-parse ladder friction (552 violations
before any corruption), and @n occurrence suffixes cascade under
damage, so cross-version label recall needs base-label multiset
comparison rather than exact suffixed labels.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018bhP89cYSdEEjHNPnxacns