claims declared UNIQUE (..., source, user_id). Every objective claim has
user_id IS NULL, and under default NULLS DISTINCT semantics Postgres treats
those rows as unique, so the ON CONFLICT DO UPDATE / DO NOTHING clauses in
db.service and mb-spine-writer never fired. Re-enrichment inserted a fresh
duplicate every run instead of reinforcing.
Live data: 236 duplicate groups, 2110 excess rows, worst single claim 86
copies, ~15% of 13,910 claims. claim_fusion is SUM(trust * confidence *
recency), so one edge could carry 86x its intended weight — the likely
cause of repetitive recommendations, and almost certainly the root of
d497588 (claim_fusion MV duplicate-key failure).
Migration 20260730_claims_dedup_nulls_not_distinct, two phases in one
transaction. Dedup MUST precede the constraint or adding it fails.
Phase 1 collapses each group into its most recently reinforced row,
carrying forward MAX(last_reinforced_at), MAX(evidence_at) and
MAX(confidence) — reinforcement recency would otherwise be lost by simply
deleting extras. The MAX(...) OVER grp and ROW_NUMBER() OVER ordered
windows are deliberately separate: an ORDER BY inside the window makes the
default frame UNBOUNDED PRECEDING TO CURRENT ROW, which turns MAX() into a
running maximum and would silently keep the wrong confidence.
Phase 2 drops the old constraint by matching its definition rather than its
name, because the live DB has drifted and its autogenerated name is
truncated at 63 characters.
Verified on a scratch PG16 seeded with the old schema plus a 3-row
duplicate group, a distinct-source singleton and a real-user_id row:
UPDATE 3 / DELETE 2, keeper retained the group max of each field from three
different rows, re-run is a no-op, and a subsequent ON CONFLICT DO UPDATE
with user_id = NULL fires correctly.
REVIEW-2026-07-30.md finding 4.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
kami
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