[codex] Round-trip turn state through compact

[aibrahim-oai]

Summary

Carry opaque turn state through remote compaction using the active model client session.

• inline and pre-turn compaction receive the session's current value
• a compact response can replace the value used by subsequent sampling
• standalone compaction uses isolated state that does not leak into user turns

Stack

1. [codex] Make turn state replaceable #27930 — replaceable HTTP turn state
2. [codex] Round-trip turn state through compact #27931 — compact round-trip (this PR)
3. [codex] Send request-scoped turn state over WebSocket #27929 — WebSocket request metadata

Coverage

• pre-turn compaction replays its returned value to sampling
• previous-model pre-turn compaction is replaced by the current model's response
• inline compact round-trips updates over HTTP for both compact protocols
• standalone compact remains isolated for both compact protocols

[aibrahim-oai]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reconnect before sampling with new compact state

When remote compaction runs on a ModelClientSession that already has an open Responses websocket (for example after prewarm or a mid-turn sample), this call stores the compact response's x-codex-turn-state, but websocket_connection later reuses the existing connection and only builds/replays headers when opening a new one. The post-compact sample can therefore continue on the old route instead of using the compact state; reset or reconnect the websocket when compaction updates the turn state.

Useful? React with 👍 / 👎.

[aibrahim-oai]

Closing this stack to replace it with one consolidated PR.

[aibrahim-oai]

Replaced by #27996.