Resolve Client.Python-001/002/004/006/007/008/010/011/012 findings

Client.Python-001: dropped "scaffold" from the stale pyproject description.
Client.Python-002 (re-triaged): stale finding — MxGatewayCommandError is
already exported and in __all__; no change needed.
Client.Python-004: removed the dead `closed` variable in _smoke; the CLI
smoke now uses `async with session`.
Client.Python-006: close() on both clients and Session had an unlocked
check-then-set race; `_closed` is now set before the await.
Client.Python-007: gateway stream iterators now share one helper that
explicitly catches CancelledError and cancels the call.
Client.Python-008: to_mx_value now rejects nan/inf; float/bytes mapping
documented.
Client.Python-010: removed the circular-import-workaround late imports in
favour of TYPE_CHECKING / module-scope imports.
Client.Python-011: ensure_mxaccess_success no longer treats a proto3-default
success==0 with an unset category as a failure.
Client.Python-012 (Won't Fix): invoke_raw deliberately skips MXAccess-failure
detection for parity tests; documented the contract instead.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/python/src/mxgateway/session.py

@@ -3,11 +3,15 @@
 from __future__ import annotations
 
 from collections.abc import AsyncIterator, Sequence
+from typing import TYPE_CHECKING
 
 from .errors import ensure_mxaccess_success
 from .generated import mxaccess_gateway_pb2 as pb
 from .values import MxValueInput, to_mx_value
 
+if TYPE_CHECKING:
+    from .client import GatewayClient
+
 MAX_BULK_ITEMS = 1000
 
 
@@ -36,7 +40,13 @@ class Session:
         await self.close()
 
     async def close(self, *, client_correlation_id: str = "") -> pb.CloseSessionReply:
-        """Close the gateway session. Repeated calls return a local closed reply."""
+        """Close the gateway session. Repeated calls return a local closed reply.
+
+        Idempotent, including under concurrent calls: ``_closed`` is set
+        before the ``CloseSession`` RPC is awaited so a second coroutine
+        entering ``close()`` while the first RPC is in flight returns the
+        local closed reply instead of issuing a second ``CloseSession``.
+        """
 
         if self._closed:
             return pb.CloseSessionReply(
@@ -44,15 +54,14 @@ class Session:
                 final_state=pb.SESSION_STATE_CLOSED,
                 protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
             )
+        self._closed = True
 
-        reply = await self.client.close_session_raw(
+        return await self.client.close_session_raw(
             pb.CloseSessionRequest(
                 session_id=self.session_id,
                 client_correlation_id=client_correlation_id,
             ),
         )
-        self._closed = True
-        return reply
 
     async def invoke(self, command: pb.MxCommand, *, correlation_id: str = "") -> pb.MxCommandReply:
         """Invoke a raw command and enforce gateway and MXAccess success."""
@@ -66,7 +75,15 @@ class Session:
         *,
         correlation_id: str = "",
     ) -> pb.MxCommandReply:
-        """Invoke a raw command and preserve the raw reply."""
+        """Invoke a raw command and preserve the raw reply.
+
+        Enforces gateway protocol success only — unlike :meth:`invoke`, it
+        does not run MXAccess-failure detection. An MXAccess HRESULT or
+        ``MxStatusProxy`` status failure is left embedded in the returned
+        reply and no ``MxAccessError`` is raised. Parity-test callers must
+        inspect ``protocol_status``, ``hresult``, and ``statuses`` on the
+        reply themselves.
+        """
 
         return await self.client.invoke_raw(
             pb.MxCommandRequest(
@@ -399,6 +416,3 @@ class Session:
 def _ensure_bulk_size(name: str, count: int) -> None:
     if count > MAX_BULK_ITEMS:
         raise ValueError(f"{name} bulk commands are limited to {MAX_BULK_ITEMS} item(s)")
-
-
-from .client import GatewayClient  # noqa: E402