Cross-provider audit R5 + R2-residual: BackendToolCall items round-trip
as their typed shapes with provider-issued ids (grok x_search
CustomToolCall, web_search/code_interpreter calls) and Reasoning items
carry model-bound encrypted payloads — replaying either to a DIFFERENT
Responses target names undeclared tools / undecryptable material → 400.
New transform_items_for_responses pre-pass: each [Reasoning|
BackendToolCall]* Assistant run carries provenance in
AssistantItem.model_id; on confirmed mismatch with the request's target
model, Reasoning siblings are dropped and BackendToolCall demoted to the
same text summary the Messages/ChatCompletions builders already emit.
Same-model and unknown-provenance turns stay byte-verbatim (KV-cache
prefix stability preserved). The legacy-upgrade round-trip test now
models the same-model continuation it always described.
Part 5 of the cross-provider replay audit.
Verified: sampling-types 290 + downstream 5794 green, clippy clean.
ZacharyZhang-NY
40c71a8343