Missing prompt-level _meta support in MCPServer.prompt() and Prompt model

Initial Checks

• I confirm that I'm using the newest release of my line (the latest 2.x, or the latest 1.x if I'm still on v1)
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Release line

2.x (current stable)

Description

Description

The 2026-07-28 specification defines the optional _meta field on the Prompt schema. While other decorators like @mcp.tool support meta and pass it down as _meta on serialization (e.g., in MCPServer.list_tools). The @mcp.prompt decorator and the high-level Prompt classes are missing support for meta.

Expected Behavior

Including meta on @mcp.prompt does not incur a type error and returns _meta for the prompt on list_prompts.

Example Code

from mcp.server.mcpserver import MCPServer

# ATTEMPTING TO USE METADATA ON PROMPTS
mcp = MCPServer("MetaTestServer")

# This currently raises a TypeError because meta is not a parameter in @mcp.prompt
@mcp.prompt(name="code_review",title="Code Review",
            description="Review code with specific metadata rules",
            meta={"strictness": "high"})
def review_code(code: str) -> str:
    return f"Review this: {code}"
   
# 2. EXPECTED BEHAVIOR
# If the decorator parameter was supported, list_prompts should return prompt with _meta:
# listed_prompts = await mcp.list_prompts()
# assert listed_prompts[0].meta == {"audience": "strictness": "high"}

Python & MCP Python SDK

- Python: 3.12+
- MCP Python SDK: 2.2.0

从 MCPServer.prompt 和高层 Prompt 模型开始，然后跟踪 list_prompts 如何序列化 prompt 字段。确认 @mcp.tool 如何接受 meta，以及其 list 操作如何输出 _meta；完成的标准是 @mcp.prompt 接受元数据时不会产生 TypeError，并且 list_prompts 将其作为 _meta 返回。