G37 -- Commit banked work the moment it exists

A bank is committed before the next command that can touch the source tree — a gate is one. A dirty source tree is never blind-reverted; banks are counted from the source, and "banked" is written only from the tool's printed success line. provenance: BFM R42 + R66; a gate that destroyed 61 banks; two ledger messages that claimed banks that had not happened