Function classify_claim 

pub fn classify_claim(changed: usize) -> ClaimOutcome

Classify an atomic claim attempt from the affected-row count (INV-5).

changed is the number of rows the conditional UPDATE reported modifying:

• 1 → ClaimOutcome::Won
• 0 → ClaimOutcome::Lost
• anything else → storage invariant violation; returns Lost conservatively. Adapters should log an internal error when changed > 1.