feat: add prompt opening behavior modes

backend/services/brains/base.py

@@ -132,6 +132,9 @@ class BaseBrain:
     async def on_greeting_finished(self) -> None:
         """Continue startup after the shared greeting has actually played."""
 
+    async def on_interruption_processed(self) -> None:
+        """Observe that an output interruption reached assistant aggregation."""
+
     def prepare_greeting_context(
         self,
         greeting: str,
@@ -214,6 +217,8 @@ class Brain(Protocol):
 
     async def on_greeting_finished(self) -> None: ...
 
+    async def on_interruption_processed(self) -> None: ...
+
     def prepare_greeting_context(
         self,
         greeting: str,