A cron job ("Daily Buzz Report") died with 'AIAgent' object has no
attribute '_claim_stream_writer'. The #65991 single-writer fence lives on
AIAgent (run_agent.py), but the streaming paths that use it live in other
modules — chat_completion_helpers (chat / anthropic / bedrock) and
codex_runtime (codex responses) — and called it directly as
agent._claim_stream_writer() / agent._stream_writer_is_current(). That makes
those modules hard-depend on the method being present on whatever object is
passed as agent.
The fence is an *additive* safety net that may only ever drop a provably
superseded stream, never the sole legitimate writer. But the direct calls
turned any agent that doesn't expose it — a version-skewed checkout (the
streaming helper module newer than run_agent), a hot-reloaded gateway mid
git-pull, a duck-typed agent, or a test double — into a fatal AttributeError
that aborts the whole turn (and, on cron, fails the job).
Route every cross-module claim/check through agent/stream_single_writer.py.
claim_stream_writer(agent) returns 0 when the fence is unavailable (or
raises), and stream_writer_is_current(agent, token) treats a 0 token or an
absent guard as "current" — so a guard-less agent degrades to "no fence"
instead of crashing, while a real AIAgent keeps the full single-writer
protection. Internal self.* uses inside run_agent are unchanged (self is
always a full AIAgent there).
