Fix codex call

Codex client never returns a cut stream as an answer (0.10.2) (#56)

The subscription backend only streams. A stream that closed before
response.completed returned its partial text, so callers parsed empty or
truncated JSON (a breakdown's location step failed on both). Such a
stream is now retried twice and then raised; response.incomplete reports
its reason; the completed response's output text is preferred over the
joined deltas.