v0.18.2

Fixed

• thread/pool: Cancel of a child that is parking — its approval requests already mirrored on the parent's Pending and its receipt already reading parked, the pool not yet at rest with it — now keeps the parked-child promise: the settlement is recorded before Cancel returns. The pool took such a child for a running one: Cancel asked the (already ended) run to stop and returned at once, the receipt still parked, and the park settled it canceled a moment later (TestCancelParkedChildBesideARunningSibling on CI: "receipt when Cancel returned = {… State:parked …}, want canceled"). Cancel now waits for the park to finish (its ctx bounds the wait); the park reads the cancel, closes the boundary and settles canceled, as before. Cancel's godoc and docs/thread-operations.md say so. TestCancelWhileParkingSettlesBeforeReturning.