swarm.matrix.enable was the last toggle still spelled swarm.*, which
is the namespace every host in the swarm agrees on - and "does this
host run the homeserver" is exactly what differs between them. It
moves to deploy.matrix.enable with the rest; the genuinely swarm-wide
matrix settings stay where they are.
mkRenamedOptionModule keeps existing configs evaluating with one
warning naming both paths.
The sweep for readers had to be unanchored and cross-language: three
of them were outside nix, including a hive-c0re error message telling
the operator to set the old name. A dotted grep also cannot see the
rename module's own list form, so that was checked separately.
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