The two callout assertions guarded the halves the server verifies with.
The responder needs the other halves, and nothing related them: a config
supplying only the public keys satisfies both, renders a syntactically
valid auth_callout block, and defines no responder unit.
Callout with no responder is the fail-closed state, so that queue refuses
every client — and a NATS denial arrives as a timeout, so the symptom is
every consumer hanging with nothing logged anywhere.
The build-time config check does run in this case and passes, because the
config is valid; what is missing is a unit, and the absence of a unit is
not an event.
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