The pre-push comment-block lint rejected two 40-line doc blocks, correctly: the
module doc and `rebuild_subtree`'s now carry the trigger and a pointer, and the
reasoning lives in a new `#### Braces` section.
That move surfaced a third doc the resource change had falsified. The scheduler's
lease-acquirer list still named `StopForUpdate` / `Swap` / `Signal` / `Drain`,
all of which are now exempt. The list now separates container-affecting nodes
from braces, and says why the rebuild subtree's members are exempt for a
different reason than `MetaSync` / `Prebuild`: they do touch the container, but
their brace holds the lease above them.
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