The endpoint ended after MOSAIC_FIXTURE_TTL_S, but init passed it only PATH, so
the lifetime was always the 14400 s default. Its record stayed after it ended,
and init refused fixture-exists until `dev fixture stop`.
init now takes --ttl SECONDS (0 = no expiry; otherwise 60 to 2147483, the
longest delay a Node timer holds; the default stays 14400), passes it to the
endpoint, and records ttlSeconds and expiresAt. /health and status report them.
A record whose pid is no longer the endpoint is stale: init removes it and says
which pid it replaced. A live endpoint still refuses fixture-exists.
A running bus keeps the endpoint it read at start, so after a replacement
the bus needs a restart; --ttl 0 avoids the expiry in the first place.
jason.woltje