fix: drop the redundant _request_is_current() from the first-event stamp guard

_on_event is only ever installed as on_event=_fenced(_on_event), and _fenced
already refuses every call once the request is retired, so the inner predicate
could never be false when reached. Comment now points at the fence.

agent/codex_runtime.py

@@ -951,9 +951,9 @@ def run_codex_stream(agent, api_kwargs: dict, client: Any = None, on_first_delta
     def _on_event(event: Any) -> None:  # TTFB/activity touch — once per SSE event.
         now = time.time()
         # Lifecycle frames can precede text, so the first accepted parsed event is the Responses
-        # equivalent of Chat Completions' first chunk. Preserve the per-attempt reset and never let
-        # a retired worker overwrite the timestamp owned by a newer request.
-        if getattr(agent, "_last_api_first_chunk_at", None) is None and _request_is_current():
+        # equivalent of Chat Completions' first chunk. Preserve the per-attempt reset; the ``_fenced``
+        # wrapper around this callback already keeps a retired worker from overwriting a newer request.
+        if getattr(agent, "_last_api_first_chunk_at", None) is None:
             agent._last_api_first_chunk_at = now
         has_progress = _codex_event_has_content(event)
         if watchdog_state is not None: