The one-time 7→8 layout migration rescues the head branch's entities
(branches/<head>/entities/* → entities/*), then drained the entire
branches/<head>/ directory. Any durable state a 7.x engine wrote under the head
branch OUTSIDE entities/ — a branch-scoped index, blob area, or field registry —
would be silently deleted by that drain, the same failure class as the VFS
content blobs a 7.x store kept in _cow/.
Guard it: after the entity move, list what remains under branches/<head>/ and
exclude entities/. If anything survives, it is non-entity durable state, so
PRESERVE the branch (skip removeRawPrefix) and warn loudly with the leftover
keys — recoverable, not lost. A clean branch (only the moved entities) still
drains exactly as before. Adds a PARITY GUARD test to the 7→8 migration suite.
David Snelling
a93bb4e85f