# K1671–K1675 complete transaction admission

A bounded journal reserves the header, every metadata record and the commit
slot together before issuing any device request. A three-record transaction
needs five logical slots. Exactly five remaining slots admit the last complete
transaction; four remaining slots return `Full` with unchanged reservation state.
Invalid record counts and exhausted 16-bit capacity cannot overflow counters.

The local tests exercise exact fit and one-record shortage. A mutant omitting
the capacity guard must fail. Guest evidence must pair this admission decision
with the disposable writer: a full journal must not issue a partial second
transaction, as checked by device trace and post-run disk bytes.

These are logical reservation units, not a general on-disk ring allocator. The
writer currently uses fixed disposable sectors. Slot recycling, concurrent
reservation, durable journal allocation and production release remain open.