Flag routed from the UI stream's rename-shuffle fix (a9339b3): the
positions ledger was the one remaining plain writeFileSync among the
rewritable ledgers — a torn write (crash mid-write) could replace it
with a half-written file, and readPositionMap parses a failure to {}
(honest empty, but the resting layout would be silently lost). The
tmp+rename pattern from rewriteLedgers, ~4 lines up the file: write a
uniquely-named temp, rename over the ledger — a crash leaves either the
old ledger intact or the new one complete, plus an orphan .tmp-*.
879/879 tests, typecheck/lint/build green; live-verified via the node
deletion's positions prune (no temp residue, valid JSON).
amosblomqvist
10be308ab6