startGatewayRuntimeServices() previously started both the cron
scheduler AND heartbeat runner BEFORE gateway sidecars finished
initialising. Because chat.history is marked unavailable until
sidecars complete, any cron job or heartbeat tick that called
chat.history during this window received a hard UNAVAILABLE error.
Fix: create a noop heartbeat placeholder in the early
startGatewayRuntimeServices() call, then activate the real
heartbeat runner, cron scheduler, and pending delivery recovery
in a new activateGatewayScheduledServices() function that runs
AFTER startGatewayPostAttachRuntime() completes.
channelHealthMonitor and model pricing refresh remain in the
early call since they do not depend on chat.history.
Root cause analysis by luban, cross-validated by tongluo.
Reviewer feedback addressed: heartbeat runner is now also
deferred (previously only cron was deferred).
92776b8d77