Module router 

Turning a decoded envelope into a method to dispatch, without naming one.

The trait is the seam, and it is monomorphised on purpose

MethodTable knows a method’s name and can turn its raw params into a typed value, but it is declared by the consumer and implemented by whichever protocol module is in play. Nothing here mentions tools/call or initialize; that is the whole point of the split, and it is what lets T27 and T29 add A2A and ACP without touching a line of this file.

The trait is generic over its own MethodId and its own decoded params rather than erasing them to Box<dyn Debug>. Erasing would put a heap allocation on the path this whole layer exists to keep allocation-free, and it would throw away the type the caller needed before anything could be dispatched. The associated types are what “consumed through impl MethodTable so it monomorphises” means in practice.

Three type parameters, because a reply carries nothing

Routed has one type parameter per arm that holds a value: the request params, the notification params, and nothing for the reply. A single parameter would mean either erasing the two params types into one or manufacturing a value the reply arm never reads, and both are worse than carrying the third type. It is the same argument as not erasing to Box<dyn Debug>, applied to the reply case.

Where an error is raised

A method that is not in the table is -32601 and a params shape that does not fit is -32602 — both decided here, from the same code, whether the table is MCP’s or A2A’s. The message is the only part a protocol supplies. That is the difference between “route” and “dispatch”, and keeping the seam between them is what lets a later task fill in the second half without rewriting the first.

Enums

ReplyPayload

The undecoded half of a reply.

RouteError

Why a frame was refused.

Routed

A routed message: the method it names and its params, already typed.

Traits

MethodTable

The set of methods one protocol speaks, and how to decode each one’s params.

Functions

route_frame

Decodes a frame and routes every message in it, refusing a batch when policy says this session does not accept one.

route_one

Routes one message, decoding its params into the table’s own types.

Type Aliases

RoutedFrame

What a routed frame contains, for one table.

RoutedMessage

The same, for a single message.