An explicitly-null key (port: null, bare port:, debug: ~, metrics
subkeys, and every other known key) previously fell through the ok/nil
check in the strict getters and silently took the default, violating
the no-silent-fallback rule and contradicting metrics: null which
already aborted. validateKnownKeys now collects null-valued keys (top
level and metrics subkeys) and aborts naming each one, and the strict
getters and validateAllowlistHostsValue error on null instead of
defaulting as defense in depth. This also replaces the unhelpful
'value <nil> is not a map of metrics settings' rendering for
metrics: null with the null-specific message.
sneak
c0d325156f