Bounding is_running turned a hung systemctl into "not running" for
callers that record or act on the answer: the broad-stop restore set
dropped the agent, start_many could rebuild-and-restart a running
agent, reconcile could seed Offline. is_running is back to the
unbounded call it was.
The periodic workers read through the bounded running_state instead:
crash_watch (unchanged), and the swarm_agent_status publisher via the
new container_view::read_agent_status_bounded, which skips the agent
for that sweep when the unit state is unreadable. The GetAgentMeta
socket handler keeps the unbounded read_agent_status_live.
The queue's payload ceiling was justified by what the queue was about to
carry; it carries it now, so the comment says so.
The other two sites say "a hive with no queue configured". The swarm has
exactly one queue and a hive cannot lack it — only its coordinates, its
credential, or its ability to reach it. That wording is already used
everywhere else the absence is named; these two predate it.
The docs section on the agents' queue coordinates stopped at delivering
them and never said what the connection is for. It now names the subject
and the degrade rule, which is the part an operator reading an agent's
terminal at the swarm needs.
Refs #3805
