[benbrandt]

The docs and MCP require type: "object" and properties on a form-mode requestedSchema, but the Rust type gave both serde defaults, so the generated schema accepted {}.

• Rust: ElicitationSchema.type_ and properties no longer have serde defaults. The generated v2 schema now lists both as required. This is a breaking change for the unstable deserializer, which now rejects a schema missing either field.
• Test: the root-type test now checks that both fields are required and that other type values are still rejected.
• Migration guide: added to the list of schema tightenings, since v1 didn't require them.

v2 only.