v0.12.3

Two inert defects, fixed before something copies them

RUNPOOL_SETTLE_SECS was defined outside the configuration precedence
block, so a value in the config file beat one in the environment. The
health check did not consult the reconfiguration lock, so a check
landing while registrations were being rewritten could report a
deliberate operation as an outage.

Neither has ever fired. No action needed on upgrade.