The credential-pool Codex refresh path synced tokens from auth.json and
then POSTed the refresh_token to OpenAI's token endpoint without holding
the cross-process auth-store lock across the whole read->POST->write-back
sequence. Because Codex refresh tokens are single-use, two concurrent
Hermes processes could both adopt the same on-disk token and both POST
it; the loser got refresh_token_reused / invalid_grant.
Wrap the Codex OAuth branch of _refresh_entry in the existing shared
_auth_store_lock (reentrant, cross-process flock) using the same
extended-timeout pattern resolve_codex_runtime_credentials() already
uses. A waiting process now blocks on the lock and, once inside, the
in-lock re-sync picks up the rotated token the winner persisted and
skips its own POST. Also send User-Agent: hermes-cli/<version> on the
refresh request.
Credit @cooper-oai (#34820) for identifying the concurrent-refresh
reuse race; this ships the narrow lock-serialization fix without the
separate Codex auth-store partition.
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