Built-in default web bind address: both loopbacks and nothing else. Fastify binds localhost
as 127.0.0.1 plus ::1 when the host has it, so a page served from [::1] still reaches the
console same-origin and nginx's 127.0.0.1 upstream still answers. The plain API has one job,
on-host tooling over loopback; a device on the LAN reaches the console through nginx over h2
(2026-09-01-http2-console-streams.md §5, amendment 2026-09-03). An explicit web.host on any
layer binds what it names — an operator who wants the plain port on a LAN address writes it.
Built-in default web bind address: both loopbacks and nothing else. Fastify binds
localhostas 127.0.0.1 plus ::1 when the host has it, so a page served from[::1]still reaches the console same-origin and nginx's127.0.0.1upstream still answers. The plain API has one job, on-host tooling over loopback; a device on the LAN reaches the console through nginx over h2 (2026-09-01-http2-console-streams.md §5, amendment 2026-09-03). An explicitweb.hoston any layer binds what it names — an operator who wants the plain port on a LAN address writes it.