review: include tool-call argument tokens in tps generation window

- Bookmark first/last token timestamps on ResponseFunctionCallArgumentsDeltaEvent
  too so the tps generation window covers all event types whose tokens land in
  usage.output_tokens. Previously the numerator counted argument tokens but
  the denominator excluded their generation time, inflating tps for tool-heavy
  responses.

- Lifted the bookmarking out of the text-delta branch into a single up-front
  check covering all four token-producing event types — cleaner than
  duplicating across branches.

- Documented the single-token skip case (window collapses to 0) inline at the
  guard. TPS is undefined for a one-token response so emitting nothing is
  correct; the comment makes the intent visible to future readers.

Author: x

src/agentex/lib/core/temporal/plugins/openai_agents/models/temporal_streaming_model.py

@@ -725,6 +725,20 @@ async def get_response(
                     # Log event type
                     logger.debug(f"[TemporalStreamingModel] Event {event_count}: {type(event).__name__}")
 
+                    # Bookmark first/last token-producing events for ttft and tps.
+                    # Includes function-call argument deltas so the generation window
+                    # covers every event type whose tokens land in usage.output_tokens.
+                    if isinstance(event, (
+                        ResponseTextDeltaEvent,
+                        ResponseReasoningTextDeltaEvent,
+                        ResponseReasoningSummaryTextDeltaEvent,
+                        ResponseFunctionCallArgumentsDeltaEvent,
+                    )):
+                        now_perf = time.perf_counter()
+                        if first_token_at is None:
+                            first_token_at = now_perf
+                        last_token_at = now_perf
+
                     # Handle different event types using isinstance for type safety
                     if isinstance(event, ResponseOutputItemAddedEvent):
                         # New output item (reasoning, function call, or message)
@@ -790,15 +804,6 @@ async def get_response(
                         # Handle text streaming
                         delta = getattr(event, 'delta', '')
 
-                        # Bookmark first/last content-bearing events for ttft and tps.
-                        # last_token_at is updated on every delta so tps measures only
-                        # the model-generation window, not subsequent tool-call /
-                        # event-handler time.
-                        now_perf = time.perf_counter()
-                        if first_token_at is None:
-                            first_token_at = now_perf
-                        last_token_at = now_perf
-
                         if isinstance(event, ResponseReasoningSummaryTextDeltaEvent) and reasoning_context:
                             # Stream reasoning summary deltas - these are the actual reasoning tokens!
                             try:
@@ -1075,6 +1080,9 @@ async def get_response(
                     m.ttft_ms.record((first_token_at - stream_start_perf) * 1000, metric_attrs)
                 # tps denominator is the generation window (first→last delta), not
                 # total stream wall time — see _StreamingMetrics for rationale.
+                # Note: single-token responses (where first_token_at == last_token_at,
+                # e.g. a one-token tool-result acknowledgement) collapse the window
+                # to 0 and are intentionally skipped — TPS is undefined in that case.
                 if (
                     first_token_at is not None
                     and last_token_at is not None