additionalProperties pass-through on generated models #52

Problem

Our default mapper drops unknown fields, so a read-modify-write loses server-added fields.

Proposed change

Generate @JsonAnySetter/@JsonAnyGetter (or the serde-SPI equivalent) capturing unknown fields into an immutable snapshot taken at build(), round-tripped losslessly.

Acceptance

• Unknown fields preserved on round-trip
• Test

Depends on the RawJson tree.

Dependencies

• Blocked by Design a dependency-free four-state JSON field model for generated types #50 — needs the RawJson tree

Priority: high · Effort: medium