SEP-2260：要求服务器请求与客户端请求相关联

<Warning>

**Request Association Requirement**

Servers **MUST** send `sampling/createMessage` requests only in association with an originating client request (e.g., during `tools/call`, `resources/read`, or `prompts/get` processing).

Standalone server-initiated sampling on independent communication streams (unrelated to any client request) is not supported and **MUST NOT** be implemented. Future transport implementations are not required to support this pattern.

</Warning>

<Warning>

**Request Association Requirement**

Servers **MUST** send server-to-client requests (such as `roots/list`,
`sampling/createMessage`, or `elicitation/create`) only in association with an
originating client request (e.g., during `tools/call`, `resources/read`, or
`prompts/get` processing).

Standalone server-initiated requests of these types on independent
communication streams (unrelated to any client request) are not supported and
**MUST NOT** be implemented. Future transport implementations are not required
to support this pattern.

</Warning>

<Warning>

Servers **MUST** send server-to-client requests (such as `roots/list`,
`sampling/createMessage`, or `elicitation/create`) only in association with an
originating client request (e.g., during `tools/call`, `resources/read`, or
`prompts/get` processing).

Standalone server-initiated requests of these types on independent
communication streams (unrelated to any client request) are not supported and
**MUST NOT** be implemented. Future transport implementations are not required
to support this pattern.

</Warning>

<Warning>

`ping` is an MCP-level liveness check and **MAY** be sent by either party at
any time on an established session/connection.

In Streamable HTTP, implementations **SHOULD** prefer transport-level SSE
keepalive mechanisms for idle-connection maintenance; `ping` remains available
for protocol-level responsiveness checks.

Request-association requirements for `roots/list`, `sampling/createMessage`,
and `elicitation/create` do not apply to `ping`.

</Warning>

- The server **MAY** send JSON-RPC _requests_ and _notifications_ before sending the
- JSON-RPC _response_. These messages **SHOULD** relate to the originating client
- _request_.
+ The server **MAY** send JSON-RPC _requests_ and _notifications_ before sending the
+ JSON-RPC _response_. These messages **MUST** relate to the originating client
+ _request_.

- The server **MAY** send JSON-RPC _requests_ and _notifications_ on the stream.
- These messages **SHOULD** be unrelated to any concurrently-running JSON-RPC
- _request_ from the client.
+ The server **MAY** send JSON-RPC _notifications_ and _pings_ on the stream.
+ These messages **SHOULD** be unrelated to any concurrently-running JSON-RPC
+ _request_ from the client, **except** that `roots/list`,
+ `sampling/createMessage`, and `elicitation/create` requests **MUST NOT** be
+ sent on standalone streams.

# ❌ PROHIBITED: Standalone server push
async def background_task():
    while True:
        await asyncio.sleep(60)
        # Try to initiate sampling without any client request context
        await session.create_message(...)  # NOT ALLOWED

# ✅ SUPPORTED: Sampling during tool execution
@mcp.tool()
async def analyze_data(data: str, ctx: Context) -> str:
    # Request LLM analysis while processing the tool call
    result = await ctx.session.create_message(
        messages=[SamplingMessage(role="user", content=...)]
    )
    return result.content.text