* fix(agents): lease managed worktrees across a run with an exclusive removal claim
A resumed session's managed worktree could be removed mid-run by idle GC, a
separate remover, or a manual worktrees.gc, destroying in-flight work; a session
whose worktree was already removed was admitted anyway and ran without its
checkout.
Runs now take a shared run-lease and removal takes an exclusive claim, both held
as rows in the shared state_leases table so admission and removal serialize
through one BEGIN IMMEDIATE transaction. Lease rows carry an opaque token plus
pid and process start time; dead or reused-pid owners are pruned inside the same
transaction. Removal claims before any cleanliness or snapshot work and rejects
while a live run lease exists; a run releases only its own token. The worktree id
is resolved from the session binding or by containment over both the run cwd and
workspace dir, so a workspace-only child still leases. The git worktree lock is
retained as a secondary raw-Git guard and refcounted per process so a parent and
a same-process child do not unlock each other.
* fix(agents): serialize worktree git lock cleanup
* test(agents): seed worktree races in sqlite
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
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