A contradiction points at an error upstream (B2a)

[WaylandYang]

Implements B2a of 0017: the engine and the queue. B2b (visibility in the graph and the entity panel) stays planned.

Engine (utopia-reason): derive::contradictions measures a derivation against functional / inverse_functional / asymmetric / irreflexive with overlapping validity. Derived vs asserted comes out per item; derived vs derived is aggregated by rule pair. Five unit tests.

Queue (utopia-store, migration 0020): run records axiom_violations of kind derived_contradiction (left = the assertion hit, right = the last premise, the derived triple in detail, capped at 50 per predicate); rule clashes land in ontology_defects as rules_disagree. materialize uses the same function to hold those derivations back; an accepted pair lands on the next run. Both load edges through one timed_edges so the queue and the graph never disagree. Integration test covers block → close → land → accept → rule clash → clear.

Review: the card shows the derived line, the asserted line and one clue (stale / duplicate / unsure), with repairs right there: end date (fact_closed, new resolution), retract, see duplicates, open ontology, let both stand. The endpoint performs the repair and re-materializes. New colour token --u-contest.

Decision records: 0017 status line updated to "B2a implemented"; 0002 and 0016 carry a revision note; index row updated. This branch carries the 0017 record from #237, so #237 can be closed once this merges.

Verified end to end on the isolated DB: the card appears after "Run check", "Give the assertion an end date" closes the assertion, resolves the row and lands the derivation; a real rules_disagree surfaced in the demo KB (paired with symmetric vs allied with inverse, against asymmetry).

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