Root cause of 400 Invalid 'input[N].id': '' on chatgpt.com/backend-api/
codex/responses: the Responses input builder replayed every stored
Reasoning item verbatim, and rs::ReasoningItem.id serializes
unconditionally — so foreign items (Messages-captured Anthropic
signatures, chat-completions-synthesized reasoning, stream-delta
fallbacks, legacy upgrades — all id '') reached the wire with an empty
id the API rejects. This also self-poisoned pure codex sessions whose
reasoning arrived only as deltas.
A native item always carries a server-issued rs_* id: empty id = foreign
= unusable by any Responses provider = dropped at the builder — the
exact mirror of the Messages builder's prune_replayed_thinking. The
encrypted-only fixture that pinned the poison shape now uses a native id
(the pass-through case it always meant to cover).
Part 1 of the cross-provider replay audit (Pi transform-messages
policy: builders emit only items valid for their target).
Verified: sampling-types 286 + sampler/chat-state/shell 5791 green.
ZacharyZhang-NY
1fa87566d9