Closing a chat releases its journal before its sync drive #2064

Found while fixing #2046. When a session closes, it releases the chat's journal before its process closes the chat's sync drive. In that gap a new opener on the same computer can take the journal and resume the same fence, and then lose it when the old drive's close releases the lease.

Window: between the journal release and the old process's drive close.

Harm: not shown yet; the expected effect is a chat that shows 'available' and refuses its next send right after a quick close-and-reopen on one computer.

Repro idea: close a chat in one process and open it in another as fast as possible, many times, and check the hold and the next send.

An unfinished, unverified attempt (close the drive first) is on the branch fix/closed-chat-drive-closes-first.

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