RebuildOpts held one real parameter (relock) and one single-call-site
flag (graceful). The struct justified itself as swap-protection for two
positional bools; with graceful out of the signature there is nothing
left to swap.
graceful stays an internal switch rather than moving to the caller: it
re-parents the stop root (StopForUpdate goes from part_of(prebuild) to
part_of(signal)) rather than prepending nodes, so a caller could only
declare it by being handed the subtree's internals — and that nesting
keeps the agent lease continuous across the whole stop.
run_meta_lock no longer returns options: both fields were a pure
function of the sweep flag its caller had just passed in.
315 tests pass unchanged.
05f84191fb