Two corrections on top of the #71077 base (the whole bug class):
1. Turn boundary = last USER message, not last assistant message. A Codex
turn spans several assistant messages (assistant+tool_calls -> tool ->
... -> final assistant) whose reasoning items must replay together; the
last-assistant boundary would strip reasoning mid-chain from the active
turn (the gap flagged in PR #71077 review).
2. type="compaction" checkpoints (native server-side compaction, PR #81747)
are exempt: they carry already-pruned history, not per-turn reasoning.
Pruning filters items instead of popping the sidecar key.
Sibling site fixed in the same class: the Codex incomplete-continuation
dedup path blind-overwrote codex_reasoning_items on visually-duplicate
interim messages, which would drop the only copy of a checkpoint captured
on the earlier response. Extracted merge_interim_reasoning_items() into
agent/native_compaction.py; newer reasoning wins, prior checkpoints are
preserved unless the newer payload carries its own.
Opt-in via compression.codex_responses_native (default: false). When enabled,
gpt-5.6-family models on the direct OpenAI API (api.openai.com) or a ChatGPT
Codex subscription send context_management=[{type: compaction,
compact_threshold: N}] on Responses requests. OpenAI compacts server-side and
returns an encrypted compaction output item; Hermes captures it into the
existing codex_reasoning_items sidecar and replays it on later turns in place
of the pruned history — inheriting persistence, session replay, the
cross-issuer guard, and the encrypted-replay kill switch with zero new state.
Scope is deliberately hard-gated (agent/native_compaction.py, re-checked per
request): gpt-5.6 family only — gpt-5.1/5.2 fail server-side on the field
(HTTP 500 / stream stall, no structured rejection; live-verified) — and
direct OpenAI/Codex routes only; xAI, GitHub/Copilot, OpenRouter, relays,
and local servers never see the field.
Hermes' local compression stays armed as the fallback owner: the native
threshold is clamped ~8K tokens below the local trigger so the server
compacts first, and a structured provider rejection of context_management
disables native compaction for the session and retries without it
(one-shot guard in TurnRetryState).
Live-verified E2E on api.openai.com/gpt-5.6: server compaction fired at a
4K threshold, checkpoints captured and replayed, recall preserved across
3 turns; gpt-5.1 with the flag enabled stays clean (field never sent).
Direction credit: PR #76950 by @laryhorb explored native Responses
compaction; this is a minimal reimplementation on current main.
Teknium