An invalid_encrypted_content 400 (or the Codex 401 token_expired twin)
used to strip every cached codex_reasoning_items blob AND turn
replay off for the rest of the agent's life, so a single rotated
sealing key cost all cross-turn reasoning continuity in a long CLI
session or a cached gateway agent.
The first rejection now only strips the stale blobs (persisted messages
and the request copy the retry is rebuilt from); blobs the route mints
afterwards are sealed with its current key and keep replaying. A second
rejection means the route cannot round-trip its own fresh blobs, so
replay is disabled for the session as before: a hostile route costs one
extra 400 compared to main.
The request-copy strip is required: main's global kill switch hid that
the retry was rebuilt from api_messages, which still carried the blob.
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