S1-02 — Ledger state union

Status: Ready Goal: Model the vuln workflow ledger as a closed discriminated union.

Acceptance criteria

• All seven ledger variants exist.
• Illegal transitions are unrepresentable in constructors.
• Exhaustive match tests cover every state.

TDD plan

Red: transition-table tests fail on missing variants. Green: add models and constructors. Refactor: move repeated evidence fields into shared bases.