reasoning.encrypted_content is sealed to the Responses endpoint that
minted it. When a session switches model providers mid-conversation —
say the user runs /model gpt-5.5 after several turns on grok-4.3, or
vice versa — the persisted codex_reasoning_items carry blobs the new
endpoint cannot decrypt, and every subsequent turn fails with HTTP 400
invalid_encrypted_content.
This is the cross-issuer prevention layer. Pairs with:
* PR #33035 — runtime recovery when the HTTP 400 fires anyway
* PR #33146 — prevention for transient rs_tmp_* items
Stamps each reasoning item with the issuer kind that minted it
(codex_backend / xai_responses / github_responses / other:<url>) at
normalize time, then drops items at replay time when the active
endpoint differs from the stamp. Unstamped (legacy) items pass
through for backwards compatibility.
Cherry-picked from @chaconne67's PR #31629. Conflict against current
main (#33035's replay_encrypted_reasoning parameter) resolved as
'keep both' — the two guards compose: replay_encrypted_reasoning=False
is the session-wide kill switch, current_issuer_kind is the per-item
filter that runs only when replay is still enabled.
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