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fix: bind loopback by address and pin the sandbox port so containers work

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Two defaults that each break the Inspector inside a container.

#1951 — the web UI never loads in a VS Code dev container. `HOST` defaulted
to the NAME `localhost`, and `server.listen(port, host)` resolves a name
through `dns.lookup` and binds the SINGLE address it gets back. Since Node 17
the default result order is `verbatim`, so on a glibc Linux host — whose
/etc/hosts maps localhost to both 127.0.0.1 and ::1 — that is `::1`. The
server bound IPv6 loopback only and refused every IPv4 client, including the
dev container port forwarder. It presents as an endless spinner rather than a
connection error because the forwarder accepts on the host side before failing
to connect inward. Default to the ADDRESS 127.0.0.1 instead; an explicit
HOST=localhost is still honored as typed.

#2008 — the Apps tab is unreachable in any container. The MCP Apps sandbox
listened on an OS-assigned port, so it changed every run and could never be
named in a devcontainer `forwardPorts`, a `docker run -p`, or a tunnel. Default
it to a fixed 6275, mirroring CLIENT_PORT's fixed 6274, and retry once on an
OS-assigned port (loudly) if it is taken — the collision a dynamic default
never had.

Verified in the reporter's exact image
(mcr.microsoft.com/devcontainers/typescript-node:4-24-trixie): both listeners
come up on 127.0.0.1 and answer 200 on 6274 and 6275/sandbox.

Also EXPOSE 6275 and set MCP_SANDBOX_PORT in the image, and document both
defaults in the web README, the migration guide, and the root README's Docker
section.

Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-08-15 12:13:06 -04:00
commit adde9ccf94
1 changed files with 246 additions and 52 deletions
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AGENTS.md
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@ -17,7 +17,10 @@ v2/main/
│ │ │ # sandbox-controller.ts (MCP Apps sandbox HTTP server),
│ │ │ # inject-auth-token.ts (embeds the API token into served index.html),
│ │ │ # vite-base-config.ts (shared optimizeDeps exclusions),
│ │ │ # resolve-bind-host.ts (bind-host POLICY: refuses an
│ │ │ # resolve-bind-host.ts (bind-host POLICY: defaults to
│ │ │ # 127.0.0.1 — an ADDRESS, never the name `localhost`, which
│ │ │ # listen() resolves to a SINGLE family (::1 on glibc Linux),
│ │ │ # refusing every IPv4 client — #1951; and refuses an
│ │ │ # all-interfaces HOST unless DANGEROUSLY_BIND_ALL_INTERFACES;
│ │ │ # the all-interfaces DETECTION is core/node/hostUrl.isAllInterfacesHost.
│ │ │ # Used by both bind points — web-server-config.ts + vite.config.ts — #1795),