## Motivation and Context
The client answers server pings automatically, but the docs leave out where that applies and what the stdio transport
does with the other server-to-client requests.
The client Transports page now lists the automatic ping answer among the things the stdio transport handles,
and a note states that `ping` is the only server-to-client request answered there: a wire-level `elicitation/create`
or `sampling/createMessage` is ignored over stdio, so a server that sends one waits for an answer that never comes,
while the SEP-2322 `input_required` route works on every transport and keeps `on_elicitation` and `on_sampling` handlers
working over stdio. Without this note, the only trace of the limitation is a hung tool call.
The client Ping page now says that over HTTP a ping reaches the client only on a stream that is already open
and that the client never opens one to receive pings, so a server can only ping a client that has a stream open.
Registering `on_server_request("ping")` moves to the end of the section as the advanced option it is, together with
its side effect of opening the GET listening stream on `connect`.
The client overview mentions the automatic answer next to `MCP::Client#ping`,
and the server Ping page's Client Side section points at it.
## How Has This Been Tested?
Documentation only; the linked headings and pages exist.
## Breaking Changes
None.
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