Handle schema validation failures gracefully

[kbhadury]

When using the DefaultMcpStatelessServerHandler#handleRequest method, the SDK throws various exceptions if the incoming request doesn't adhere to the MCP schema. Here are a couple examples I've observed:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "tools/call",
  "params": {
    "name": "myTool",
    "arguments": "This should be an object!"
  }
}

This causes an IllegalArgumentException to be thrown by McpStatelessAsyncServer when Jackson attempts to parse the arguments field, which is supposed to be an Object:

java-sdk/mcp-core/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java

Lines 395 to 399 in b518393

	private McpStatelessRequestHandler<CallToolResult> toolsCallRequestHandler() {
	return (ctx, params) -> {
	McpSchema.CallToolRequest callToolRequest = jsonMapper.convertValue(params,
	new TypeRef<McpSchema.CallToolRequest>() {
	});

Here's a second example:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "tools/call",
  "params": {
    "arguments": {
      "key": "value"
    }
  }
}

In this example, the name field was omitted. This causes McpStatelessAsyncServer to throw a NullPointerException when it attempts to call name().equals(...):

java-sdk/mcp-core/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java

Lines 401 to 403 in b518393

	Optional<McpStatelessServerFeatures.AsyncToolSpecification> toolSpecification = this.tools.stream()
	.filter(tr -> callToolRequest.name().equals(tr.tool().name()))
	.findAny();

Is there a way to validate the incoming JSON against the MCP schema before passing it to the handler object? Or can the handler object be enhanced to deal with these kinds of errors more gracefully and return a friendlier error to the caller? Thanks!