Transports and the open decision

The MCP tunnel listens on loopback. Making it reachable is a separate concern with its own adapter interface, and the choice of default adapter is recorded as a decision that is proposed, not accepted. This page explains the candidates and the constraint that drives the proposal; the normative record is docs/decisions/0001-tunnel-transport.md in the repository.

The constraint that decides it

Claude Desktop can reach anything you can route to it, including a private network or a forwarded local port. claude.ai connectors cannot: they need a public HTTPS endpoint. Whichever transport becomes the default determines whether claude.ai is in scope at all.

The candidates

Cloudflare Tunnel publishes the listener at a hostname in a DNS zone the operator controls, over an outbound-only connection. No inbound ports, TLS at the edge, and Cloudflare Access available in front. It is the only candidate that serves claude.ai connectors without exposing the host. Costs: a Cloudflare account and zone, a dependency on Cloudflare’s availability, and the tunnel token as a new secret.

WireGuard gives the strongest network posture with no third party, but every client machine needs a peer configuration, and claude.ai cannot join a private network, so it serves Claude Desktop only.

SSH forwarding needs no new infrastructure beyond the SSH access the deploy workflow already uses, but it is per-machine, manual, and likewise cannot serve claude.ai.

Why the gates exist

Until the decision is accepted, the cloudflared path is deliberately double-gated: the compose service sits behind the cloudflared profile, and the in-process adapter refuses to start without --enable-cloudflared even when the config selects it. The WireGuard and SSH adapters are stubs that fail loudly and point at the decision record. The gates make the current state legible: the interfaces are final, the default is proposed, and nothing publishes traffic by accident while the proposal is open.

An extra data point

On the Cloudflare Sandboxes backend, Cloudflare Tunnel is not an optional publisher but the SDK’s native path for exposing in-sandbox services. Accepting the proposal would converge both backends on the same edge.