[adamcavendish]

Summary

Generate usable Kotlin models for named pure dictionaries and retain their flat
JSON entries through model and HTTP conversion.

Problem

A named object with only additionalProperties reaches the Kotlin emitter as an
object with no named fields. The emitter previously ignored its dictionary value
type and attempted an empty data class, which sigil-stitch correctly rejects.
Even the single-schema Labels string dictionary therefore prevents generation.

Using a Map subclass does not solve the full problem: Gson selects its built-in
map codec before the annotated adapter, discarding null entries and bypassing the
dictionary's object-root handling.

Behavior

Pure dictionary models now expose typed mutable additionalProperties storage,
defaulting to an empty map. A private Gson adapter flattens that storage directly
to JSON object keys; no additionalProperties wrapper is added on the wire.

val labels = Labels()
labels.additionalProperties["keep_key"] = "value"
val json = Gson().toJson(labels) // {"keep_key":"value"}

Keys remain verbatim, including keys resembling renamed fields or the storage
property itself. Values retain scalar, generated-model, nullable and container
types. Opaque dictionaries use JsonElement values, preserving arbitrary trees,
null entries and large numeric literals. Nested containers preserve their own
entries while ordinary model-valued leaves keep their normal Gson codecs.

Entries decode directly from the original JSON reader through their declared
native codecs. Fractional or overflowing integer values retain native decode
errors instead of being silently truncated or wrapped by tree-reader conversions.
Authored model and dictionary types use their configured model-package identities,
including inside nested containers, so Gson helpers such as TypeToken,
JsonElement, JsonNull and Gson cannot replace same-named generated models.

Aliases, recursive values, containing models and union boundaries use the same
dictionary representation. HTTP requests, successful responses and lazy typed
error bodies retain dictionary payloads. Root JSON null stays Kotlin null;
non-object roots fail instead of silently becoming empty dictionaries. Writers
restore the surrounding null policy even when serialization fails.

Boundaries

This is the pure Kotlin dictionary repair after merged union #176. The new path
applies only to objects with no named fields and explicit additional-property
value facts. Ordinary and mixed objects, tagged codecs, aliases, enum declarations,
shared IR, other-language generators and generated dependencies are unchanged.
Mixed-object additional-property preservation and multi-member allOf wire-shape
redesign remain separate. Value decoding uses the retained IR representations and
existing native codecs; this is not new JSON Schema validation or a shared-lowerer
redesign. Generating the larger wire-preservation fixture does not claim that its
separate mixed-object and composition defects are fixed.

[codecov]

Codecov Report

❌ Patch coverage is 97.63314% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/generators/kotlin/okhttp/dictionary.rs	96.69%	4 Missing ⚠️

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