Anchor one evidence item to one exact claim of the intent (objective, outcome, constraint, or edge case). Changes where the item backs, never whether it is reviewed: the item's tier is untouched.

The row-locked anchor_evidence_to_intent RPC validates the live claim and commits its anchor, join row, and reverse link atomically, so concurrent writes cannot drop it or leave the relationship partially synchronized. Emits evidence_anchored (claim kind, tier, source claim_row) and, when newly linked, evidence_linked. Review with attribution (moving an unreviewed item to backing) is a separate, session-only action in the Claim Trust Loop; this endpoint never changes triage_status. Plan: .claude/plans/evidence-trust-contract.md (Claim Trust Loop, slice A).