The matrix server-server spec resolves a portless m.server delegated
host to the federation default port 8448 (not 443 — the URL convention
that https implies 443 does not apply to the m.server field). The
gateway reused publicPortSuffix, which intentionally drops :443 for the
client base_url, so .well-known/matrix/server advertised the bare
gateway host. Peers then federated to <gatewayHost>:8448, which nothing
listens on, while the federation endpoint actually lives on the gateway
443 vhost (/_matrix/ proxied to tuwunel). Always emit the explicit port
in the federation delegation so peers reach the live 443 endpoint.
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