1. Removed the 45-day index-walk cap: it discarded the older part of a long
outage while still advancing source_max_date, permanently losing filings.
The walk now covers every unprocessed date (a large gap is one-time cost).
2. Discrepancy detection meets the immutability contract: it compares ALL source
snapshot fields (not five), read-only during stage/validate, reports the
differing accessions + fields in validation_json, and promote emits a warning
system event (in-transaction) — never mutating the stored row.
3. Malformed companyfacts (missing facts/units structure) are recorded separately
and FAIL validation, instead of silently degrading to skipped rows that the
50% backfill coverage floor could still pass.
Also corrected the stale "sum share classes" / DEI-only wording in the snapshot
model docstring and the A3 design doc to describe the us-gaap fallback.
Tests: +4 regressions (>45-day gap loses nothing, newly-added issuer backfills
without filing, malformed payload fails, shares discrepancy detected + evented).
23 passed, 1 skipped.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>