Constant SCHEMA_VERSION 

pub const SCHEMA_VERSION: i64 = 2;

The current row schema.

• 0 — pre-D-8. can_be_claimed_as_dependent_* were bare bools (unanswered indistinguishable from “No”).
• 1 — those flags became tri-state Option<bool>.
• 2 — P9: Person.blind and ScheduleAInputs.salt_use_sales_tax became tri-state; hsa_present was renamed hsa_activity (a different question); dual_status_alien and the mixed-use-mortgage box were added.

★ P9 §2.6 — there is no migration. The owner confirmed no real tax data has ever been entered, so a row at any version other than the current one REFUSES (row_to_inputs) rather than being read or per-key unlaundered. A version check cannot forget a key; a hand-written unlaunder list can, and did (Fable r4 I-4). Retire this the moment real data exists — the first real return needs true migrations, and prior-year carryforwards are exactly what a filer cannot reconstruct (FOLLOWUPS, release gate).