Missing `@JsonIgnoreProperties(ignoreUnknown = true)` on capability sub-records

Bug description

The top-level ClientCapabilities and ServerCapabilities records have @JsonIgnoreProperties(ignoreUnknown = true), but their nested sub-records do not. Since the ObjectMapper is constructed with default settings (FAIL_ON_UNKNOWN_PROPERTIES = true), any unknown field on a capability sub-object causes a deserialization failure.

This already caused a real breakage when the elicitation capability gained form and url fields (#724, fixed in #731), but the systemic issue remains — the next spec addition to any capability sub-object will break older SDK versions again.

Affected records

In McpSchema.java:

Spec reference

The spec schema explicitly states capabilities are not a closed set:

"Known capabilities are defined here, in this schema, but this is not a closed set: any client can define its own, additional capabilities."

ClientCapabilities in schema.json — additionalProperties: false is never set on any capability object or sub-object. Several sub-capabilities (sampling, elicitation, completions, logging) explicitly set additionalProperties: true.

Expected behavior

Unknown fields on capability sub-objects should be silently ignored, matching the behavior of the top-level ClientCapabilities and ServerCapabilities records.

Related

• #734 — reports the same issue for ToolCapabilities specifically
• #724 / #731 — the elicitation breakage that was fixed by adding fields, not by adding the annotation

_{AI Disclaimer}

Bắt đầu tại mcp-core/src/main/java/io/modelcontextprotocol/spec/McpSchema.java và xem xét các capability record được liệt kê, so sánh chúng với ClientCapabilities và ServerCapabilities. Hoàn thành có nghĩa là các trường không xác định trong mọi capability sub-record bị ảnh hưởng đều được bỏ qua trong quá trình giải tuần tự, bao gồm cả các elicitation record lồng nhau.