`InitializeRequest` doesn't accept non-empty Elicitation, violating 2025-11-25 spec

[overheadhunter]

Bug description
An initialize request with "capabilities":{"elicitation":{"form":{}}} causes this error:

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "form" (class io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation), not marked as ignorable (0 known properties: ])
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 72] (through reference chain: io.modelcontextprotocol.spec.McpSchema$InitializeRequest["capabilities"]->io.modelcontextprotocol.spec.McpSchema$ClientCapabilities["elicitation"]->io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation["form"])

This violates the 2025-11-25 spec.

Environment
N/A

Steps to reproduce
run test shown below

Expected behavior
test succeeds

Minimal Complete Reproducible example

@Test
void testParseInitializeRequest() throws IOException {
	String serialized = """
			{"protocolVersion":"2024-11-05","capabilities":{"elicitation":{"form":{}}},"clientInfo":{"name":"test-client","version":"1.0.0"},"_meta":{"metaKey":"metaValue"}}
			""";

	McpSchema.InitializeRequest deserialized = JSON_MAPPER.readValue(serialized, McpSchema.InitializeRequest.class);

	McpSchema.ClientCapabilities capabilities = McpSchema.ClientCapabilities.builder()
			.elicitation()
			.build();
	McpSchema.Implementation clientInfo = new McpSchema.Implementation("test-client", "1.0.0");
	Map<String, Object> meta = Map.of("metaKey", "metaValue");
	McpSchema.InitializeRequest expected = new McpSchema.InitializeRequest(ProtocolVersions.MCP_2024_11_05,
			capabilities, clientInfo, meta);
	assertThat(deserialized).isEqualTo(expected);
}

[fansanelli]

Hello,
I don't know if it may help to have a scenario, but I experienced this error after trying in VSCode the McpStatelessAsyncServer through HTTP protocol.
Cheers

[overheadhunter]

Same for me, VSCode appears to be using the new spec already, but servers using this SDK can't handle it.

In my case I was trying to include the SonarQube MCP server.

[fansanelli]

I know that maybe the proper fix is to implement the newer spec, but in the meantime this problem is blocking. Any chance to get the fix upstream?

[nquinquenel]

@overheadhunter SQ MCP Server developer here - I'll provide a fix for our next version, the JSON mapper should not fail on unknown properties.