The public MCP callback API generates a parameter alias in its schema but uses the Java parameter name when validating and binding the same call.

For example, construct a callback through ToolDefinitions.from(method) and DefaultToolCallback.builder() for:

@Tool(name = "echo_alias", description = "echo")
public String echo(@ToolParam(description = "text")
                   @JsonProperty("message_text") String message) {
    return message;
}

The callback's schema advertises message_text as required and does not advertise message. Calling it with {"message_text":"hello"} then throws IllegalArgumentException: Required parameter 'message' is missing. An optional aliased parameter is silently bound to null even when its advertised key is supplied.

I reproduced this on current master (5fe5f06) with real Zulu JDK8, using the public schema factory, callback builder, default converter and call API. Seven tests produce two assertion failures and two alias-related errors; three Java-name/empty-alias/optional-omission controls pass.

This concerns callbacks constructed through the library API. The built-in tools currently have no parameter aliases, and the agent's fixed tool scan is unchanged. I am preparing a focused fix to share the existing alias resolution between schema generation, required checks and argument binding, with regressions for ToolContext injection and unchanged Java-name fallback.