With store=False (our default for the Responses API), the API does not
persist response items. When reasoning items with 'id' fields were
replayed on subsequent turns, the API attempted a server-side lookup
for those IDs and returned 404:
Item with id 'rs_...' not found. Items are not persisted when store
is set to false.
The encrypted_content blob is self-contained for reasoning chain
continuity — the id field is unnecessary and triggers the failed lookup.
Fix: strip 'id' from reasoning items in both _chat_messages_to_responses_input
(message conversion) and _preflight_codex_input_items (normalization layer).
The id is still used for local deduplication but never sent to the API.
Reported by @zuogl448 on GPT-5.4.
Teknium
a4e1842f12