Result types should inherit from JSONRPCResponse

[maxisbey]

Problem

Result types like CallToolResult inherit from Result, not JSONRPCResponse. This means they're missing the jsonrpc: "2.0" and id fields.

Current inheritance:

Result (types.py:133)
└── meta: dict | None

JSONRPCResponse (types.py:168) - separate, not inheriting from Result
├── jsonrpc: Literal["2.0"]
├── id: RequestId
└── result: dict

CallToolResult (types.py:1363) extends Result
└── Missing jsonrpc, id fields

The SDK has to manually wrap every result to add the JSON-RPC envelope before sending (session.py:386-389):

jsonrpc_response = JSONRPCResponse(
    jsonrpc="2.0",
    id=request_id,
    result=response.model_dump(by_alias=True, mode="json", exclude_none=True),
)

Same pattern as the notification inheritance issue - might be worth rethinking the type hierarchy.

Related

• Type system complexity creating developer friction and maintenance overhead #837 (type system complexity)
• Excessive use of generics #1207 (excessive generics)

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