LogStore.open now takes the exclusive lock before it reads the file's length and scans for the end, and a read-only handle refuses to append. purge undo opens the store through the shared writer path.

A new DST sweep runs two to four writers interleaved against one log through a file that models the lock. It flags unlocked or misplaced appends as they happen, checks each writer sees everything committed before it locked and reads back its own writes, including deltas. A source check fails on any write-mode open of the store outside openStoreAppend. An e2e test races commits, tags and user-table writes on one store and counts what landed. check-in: 5c445bb3f3 user: dmestas tags: trunk, version-0.3.32