Fix guardrails failing when interrupt_response=True

src/agents/realtime/model_inputs.py

@@ -93,7 +93,17 @@ class RealtimeModelSendToolOutput:
 
 @dataclass
 class RealtimeModelSendInterrupt:
-    """Send an interrupt to the model."""
+    """Send an interrupt to the model.
+
+    Args:
+        force_cancel: If True, always send response.cancel regardless of
+            interrupt_response setting. This should be True for SDK-side interrupts
+            (e.g., guardrails) where the API doesn't know about the interrupt.
+            For user voice interrupts, this should be False (default) to allow
+            the API's automatic response cancellation when interrupt_response=True.
+    """
+
+    force_cancel: bool = False
 
 
 @dataclass

src/agents/realtime/openai_realtime.py

@@ -433,7 +433,10 @@ async def _send_interrupt(self, event: RealtimeModelSendInterrupt) -> None:
             and session.audio.input.turn_detection is not None
             and session.audio.input.turn_detection.interrupt_response is True,
         )
-        if not automatic_response_cancellation_enabled:
+        # Always cancel for force_cancel=True (e.g., guardrail interrupts)
+        # For user voice interrupts (force_cancel=False), only cancel if automatic
+        # cancellation is disabled
+        if event.force_cancel or not automatic_response_cancellation_enabled:
             await self._cancel_response()
 
         self._audio_state_tracker.on_interrupted()

src/agents/realtime/session.py

@@ -704,7 +704,9 @@ async def _run_output_guardrails(self, text: str, response_id: str) -> bool:
             )
 
             # Interrupt the model
-            await self._model.send_event(RealtimeModelSendInterrupt())
+            # Use force_cancel=True for guardrail interrupts because they are SDK-side logic
+            # and the API doesn't know about them (unlike user voice interrupts)
+            await self._model.send_event(RealtimeModelSendInterrupt(force_cancel=True))
 
             # Send guardrail triggered message
             guardrail_names = [result.guardrail.get_name() for result in triggered_results]