Dispatches inbound HTTP to the adapter registered for the first path segment.

Deliberately thin: parsing, dispatch, and turning an unregistered segment or a crashing handler into a plain status code. Everything else — signature verification, idempotency, payload shape — belongs to the adapter, because those rules differ per provider and baking any of them in here would recreate LemonGateway.Transports.Webhook inside lemon_channels.

Authenticate first where the handler can

A handler that can authenticate from the request line and headers alone — a shared token, an API key — implements LemonChannels.InboundHttp.Handler.authorized?/1, and it runs before Plug.Parsers. Otherwise an anonymous caller can make this process read and decode a body on every request and only then be told 401, which is free for them and expensive here.

Not every handler can: most providers sign the raw or parsed payload, which cannot be checked before the body exists. Those omit the callback and are parsed for as before, which is why the body limit below still matters.

Body limit

LemonChannels.InboundHttp.max_body_bytes/0, 2 MB by default — well under Plug.Parsers' 8 MB — and configurable for adapters that must accept larger payloads. Over the limit, Plug.Parsers raises and the caller gets a 413.

The limit is resolved per request rather than frozen into the pipeline at compile time, so a value set in config/runtime.exs or at boot is honoured rather than silently ignored.