services.hyperhive.swarm.controller.{enable,package,socketPath} plus the
unprivileged swarm-controller user, its runtime and state directories,
and the unit itself.
enable is deliberately not derived from services.hyperhive.enable, unlike
c0re: a swarm has one controller, so turning it on is a statement about
swarm topology rather than about whether hyperhive is installed.
The socket gets its own RuntimeDirectory. nginx reaches a unix upstream
by having the socket's directory bind-mounted into the gateway
container, and the socket is 0666 because connect needs write -- so the
directory is the only access control there is. Sharing one with the host
admin socket would hand that socket to the gateway too. The constraint
is stated at both ends, in the option description and beside the bind,
because it is invisible from either site alone; a test pins the path so
a tidying edit fails rather than reviews cleanly.
RuntimeDirectoryPreserve and the daemon's stale-socket unlink are a
pair: preserving the directory without the unlink means bind fails with
EADDRINUSE after a restart.
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