chore: import upstream snapshot with attribution

agent_runtime/__init__.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+__all__ = ["AgentLoop", "SessionIndex", "ToolRegistry", "build_runtime"]
+
+
+def build_runtime(*args, **kwargs):
+    from .loop import build_runtime as _build_runtime
+
+    return _build_runtime(*args, **kwargs)
+
+
+def __getattr__(name):
+    if name == "AgentLoop":
+        from .loop import AgentLoop
+
+        return AgentLoop
+    if name == "SessionIndex":
+        from .session_index import SessionIndex
+
+        return SessionIndex
+    if name == "ToolRegistry":
+        from .tools import ToolRegistry
+
+        return ToolRegistry
+    raise AttributeError(name)