ADR-224: Gemini keeps known Struct roots as JSON objects 

Context 

Google's Generate Content contract defines FunctionCall.args and FunctionResponse.response as JSON objects. Controlled actual adapter requests instead emit lists for empty and numeric-key maps. Six clean additional cases fail assertions with no framework errors; object-mode JSON decoding exposes the wire distinction. These are HTTP contract fixtures, not a live Gemini acceptance test.

The inherited associative decoder also loses arbitrary nested object/list kinds. A root repair cannot recover that information. That distinct audit finding remains open and must receive its own preservation design and evidence.

Decision 

Encode these two API-known roots as JSON objects when constructing the final Gemini request, including empty and numeric-key maps. Preserve their member values and current scalar/invalid result fallback. A decoded list result keeps its members at numeric object keys in the known Struct root. Do not cast nested arrays indiscriminately: actual nested lists must remain lists.

Apply the same rule to Gemini-owned native parts on replay, including already carried turns on closing and streaming requests. Preserve native order, signatures and every other member. Keep the carrier array-valued for the current metadata, public transcript and encrypted SQL state; construct the wire copy without rewriting that state. Existing foreign reconstruction and untagged OpenAI replay retain their own behavior.

Public ToolCall arguments remain arrays. No public signature, carrier field, schema, actor, approval, budget or retention change is introduced. ADR-222's native replay promise is qualified at these known JSON-object boundaries; arbitrary nested values retain their current decoded representation.

Consequences 

Empty and numeric-key arguments/results satisfy their known wire contract. Tests inspect actual serialized requests with object-mode JSON decoding and literal positive controls, rather than an associative round-trip that masks objects versus lists. Real persisted suspension/resume and selected assertion faults are required; specs and implementation are separate dependent PRs.

This decision does not close nested JSON-kind preservation. It makes no generic lossless transport, live API or new streamed-response capture claim. ADR-223's visible/native thought extraction remains independent.