The user JWT the callout issues carried no exp, so nats-server armed no
expiry timer and a connection kept its grant until the client dropped it:
a deleted or re-minted agent queue secret, a removed OIDC client or an
expired access token never reached a live connection.
Every issued user JWT now expires at the presented OIDC token's exp
(read from the introspection answer) or an hour after issue, whichever
is sooner; the agent queue-secret path has no exp of its own and gets
the hour. Every queue client reconnects through an auth callback that
re-reads or re-mints its credential, so the forced reconnect presents a
current one.
Fixes#5432
e405c2b098