PR #2974 whitelisted three reasoning fields (reasoning, reasoning_details,
codex_reasoning_items) for the gateway's simple-text replay branch. Three
more fields were added to the DB later but the whitelist was never updated:
- reasoning_content: provider-facing thinking text. _copy_reasoning_content_for_api
promotes 'reasoning' -> 'reasoning_content' at send time only when the
strings happen to match. Carrying the original verbatim avoids loss
for providers that return them as distinct fields (DeepSeek/Kimi/
Moonshot thinking modes), and preserves the empty-string sentinel
that DeepSeek V4 Pro requires for thinking-mode replay.
- codex_message_items: exact assistant message items with 'phase'.
OpenAI docs: 'preserve and resend phase on all assistant messages —
dropping it can degrade performance.' Required for prefix cache hits.
No recovery path exists — once dropped, gone.
- finish_reason: informational; cheap to keep so transcripts replay
identically across CLI and gateway.
The CLI is unaffected because cli.py keeps the live in-memory message list
across turns (cli.py:10046 'self.conversation_history = result["messages"]').
The gateway rebuilds agent_history from the SQLite transcript on every turn,
so any field stripped during replay is silently lost.
Refactors the inline whitelist into a module-level _build_replay_entry()
helper so the contract can be unit-tested. 16 new tests pin the field set
and falsy-value handling.
Verified end-to-end: DB stores all 8 fields, replay now preserves all 8
(was preserving only 5 for assistant text turns).
