feat(core,backends,frontends,storage): conversations, inject queue, session pool, gateway mcp tools, api frontend

src/beaver_gateway/core/turn_capture.py

@@ -35,3 +35,5 @@ class TurnCapture:
     """Backend session that ran the turn; persist and pass back as ``session_id``."""
 
     usage: TurnUsage | None = None
+    interrupted: bool = False
+    """The turn was cut by ``interrupt()`` (urgent inject), not by an error."""