PR #14193 routed warm reattach and deep-buffer snapshots through
overlayDurableRestoreSnapshot, which joined a single process-wide
checkpoint tail with no deadline. One never-settling checkpoint blocked
every daemon-backed terminal from reattaching.
Checkpoint exclusivity only protects one session directory's
tmp-write/rename pair, so serialize per session instead. Reattach now
waits on a bounded deadline and degrades to the daemon's live window;
the abandoned compact keeps running and still commits, so a blown
deadline costs restore depth for one reattach, never durable history.