Expand description
Server — the HTTP listener and accept loop.
SP-streamable-http §4.1 + §4.5: the listener exposes a single POST /mcp route by default, but ServerBuilder::build returns the
axum::Router so adopters can extend it with their own routes
(Celia’s /chat/stream, healthkit’s bulk-export progress, etc.)
before serving. The bound Server carries the shutdown handle and
the local_addr so tests can dial in.