Update send_notification method to properly construct JSON-RPC notification objects with jsonrpc version and method fields.
This ensures notifications conform to the JSON-RPC 2.0 specification when sent over HTTP transport.
https://www.jsonrpc.org/specification#notification
Another goal is to standardise the `send_notification` interface.
Before the revision, it was sufficient to pass the method and parameters in the case of stdio.
However, in the case of Streamable, a hash based on the JSON-RPC specification must be passed.
Currently, MCP has three versions: 2024-11-05, 2025-03-26, and 2025-06-18.
- https://modelcontextprotocol.io/specification/2024-11-05/basic/transports (stdio and HTTP with SSE)
- https://modelcontextprotocol.io/specification/2025-03-26/basic/transports (stdio and Streamable HTTP)
- https://modelcontextprotocol.io/specification/2025-06-18/basic/transports (stdio and Streamable HTTP)
The newer specification supports stdio and Streamable HTTP as transport mechanisms.
Only the oldest version, 2024-11-05, supports stdin and HTTP with SSE,
but that version is now considered legacy.
Given the current behavior of the Ruby SDK, it likely makes more sense to set
the default protocol version to the latest one, 2025-06-18, rather than the oldest, 2024-11-05.
Ideally, the implementation should adjust its behavior based on the version,
but this PR is limited to updating the default protocol version only.
## Motivation and Context
Currently, MCP supports the following three protocol versions:
"2025-06-18", "2025-03-26", and "2024-11-05".
https://modelcontextprotocol.io/introduction
As shown in the changes to `test/mcp/configuration_test.rb`,
the `protocol_version` value is not currently being validated,
which allows unexpected `protocol_version` values to be accepted.
This PR ensures that only supported protocol versions are accepted.
## How Has This Been Tested?
Existing tests have been updated and new tests have been added.
## Breaking Changes
None. If it becomes an issue, it means a value that was not originally intended has been used.
## Additional context
While one possible approach might be to fall back to a default protocol version
when an invalid `protocol_version` value is provided,
this PR opts to reject invalid `protocol_version` values explicitly.
The reasoning is that encouraging users to provide intentional,
valid input is preferable to silently falling back to a default,
which could lead to unexpected behavior.
Even though the 'tools/call' request to 'notification_tool' is successful and an 'MCP::Tool::Response' is returned, the logger still prints 'Error:'.
```
% ruby examples/streamable_http_client.rb
=== MCP SSE Test Client ===
[CLIENT] INFO 15:41:04.696 - Initializing session...
[CLIENT] INFO 15:41:04.698 - Session initialized: SESSION_ID
[CLIENT] INFO 15:41:04.698 - Server info: {"name" => "sse_test_server", "version" => "0.1.0"}
[CLIENT] INFO 15:41:04.698 - Connecting to SSE stream...
[CLIENT] INFO 15:41:04.698 - SSE stream connected successfully
=== Available Actions ===
1. Send custom notification
2. Test echo
3. List tools
0. Exit
Choose an action: 1
Enter notification message: notification test
Enter delay in seconds (0 for immediate):
[CLIENT] INFO 15:41:11.248 - SSE data: {"jsonrpc":"2.0","id":"0f657eeb-3e05-47bb-b7b4-898e2cb503af","result":{"content":[{"type":"text","text":"Notification: notification test (timestamp: 2025-06-21T15:41:11+09:00)"}],"isError":false}}
[CLIENT] ERROR 15:41:11.249 - Error:
=== Available Actions ===
1. Send custom notification
2. Test echo
3. List tools
0. Exit
```
It is probably trying to output an MCP::Tool::Response, but these appear in the SSE stream. Therefore, the response it is handling this time should either be accepted or an error.
I modified it so that it could handle them.
