Minimal structural validation of tool arguments against a JSON Schema.

This is a deliberately small subset of JSON Schema, sufficient to catch the common argument mistakes the DSL's input_schema describes, without pulling in a full validation dependency. It validates type (object, array, string, number, integer, boolean, null, and union types such as ["string", "null"]), object properties, required and additionalProperties: false, array items, and enum. Other keywords (minLength, pattern, format, ...) are ignored rather than enforced.

Schema keywords may be keyed by string or atom (so %{"type" => "object"} and %{type: "object"} both validate); the values being validated come from JSON and are expected to be string-keyed. For full JSON Schema validation, validate in your handler with a dedicated library (e.g. :ex_json_schema).