Clarify SessionClosedRiverServiceException

Author: blast-hardcheese

src/replit_river/error_schema.py

@@ -17,9 +17,9 @@
 # ERROR_CODE_CANCEL is the code used when either server or client cancels the stream.
 ERROR_CODE_CANCEL = "CANCEL"
 
-# ERROR_CODE_SESSION_CLOSED is the code used when either server or client closes
-# the session.
-ERROR_CODE_SESSION_CLOSED = "CLOSED"
+# SYNTHETIC_ERROR_CODE_SESSION_CLOSED is a synthetic code emitted exclusively by the
+# client's session. It is not sent over the wire.
+SYNTHETIC_ERROR_CODE_SESSION_CLOSED = "SESSION_CLOSED"
 
 # ERROR_CODE_UNKNOWN is the code for the RiverUnknownError
 ERROR_CODE_UNKNOWN = "UNKNOWN"
@@ -82,14 +82,12 @@ class StreamClosedRiverServiceException(RiverServiceException):
     pass
 
 
-class SessionClosedRiverServiceException(RiverServiceException):
+class SessionClosedRiverServiceException(RiverException):
     def __init__(
         self,
         message: str,
-        service: str | None,
-        procedure: str | None,
     ) -> None:
-        super().__init__(ERROR_CODE_SESSION_CLOSED, message, service, procedure)
+        super().__init__(SYNTHETIC_ERROR_CODE_SESSION_CLOSED, message)
 
 
 def exception_from_message(code: str) -> type[RiverServiceException]: