fix: accept logging/setLevel and ping before initialized notification

[DaleSeo]

Fixes #704

Motivation and Context

VS Code's MCP client sends a logging/setLevel request right after the server responds to initialize, but before the initialized notification. The server expects a notification at that moment and errors out on any other message, which causes the entire handshake to fail.

The MCP lifecycle spec states: "The server SHOULD NOT send requests other than pings and logging before receiving the initialized notification." This means the server can send log messages during initialization, so it's reasonable for a client to set log levels before sending initialized. The client side of this codebase already handles the symmetric case with a loop, and this fix aligns the server with that same approach.

rust-sdk/crates/rmcp/src/service/client.rs

Lines 103 to 139 in 5c5a2e7

	// Server could send logging messages before handshake
	ServerJsonRpcMessage::Notification(mut notification) => {
	let ServerNotification::LoggingMessageNotification(logging) =
	&mut notification.notification
	else {
	tracing::warn!(?notification, "Received unexpected message");
	continue;
	};
	let mut context = NotificationContext {
	peer: peer.clone(),
	meta: Meta::default(),
	extensions: Extensions::default(),
	};
	if let Some(meta) = logging.extensions.get_mut::<Meta>() {
	std::mem::swap(&mut context.meta, meta);
	}
	std::mem::swap(&mut context.extensions, &mut logging.extensions);
	if let Err(error) = service
	.handle_notification(notification.notification, context)
	.await
	{
	tracing::warn!(?error, "Handle logging before handshake failed.");
	}
	}
	// Server could send pings before handshake
	ServerJsonRpcMessage::Request(ref request)
	if matches!(request.request, ServerRequest::PingRequest(_)) =>
	{
	tracing::trace!("Received ping request. Ignored.")
	}
	// Server SHOULD NOT send any other messages before handshake. We ignore them anyway
	_ => tracing::warn!(?message, "Received unexpected message"),
	}
	}

How Has This Been Tested?

Added integration tests. I also manually verified the fix on VSCode.

Breaking Changes

None. The change only relaxes what the server accepts during initialization; the error path for truly unexpected messages is unchanged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed