feat(mcp/v2): MCPServerManagerV2 skeleton + flag-gated injection

Step 6a of the egress cutover. MCPServerManagerV2 subclasses v1's MCPServerManager with no overrides
yet, so behavior is identical. The composition root selects it via _make_global_mcp_server_manager()
when LITELLM_USE_V2_MCP_EGRESS is set (lazy import avoids the subclass import cycle); flag-off stays
v1 exactly. Verified at startup in both flag states. The per-server egress overrides
(UpstreamConnection + resolve()) land in 6b/6c.

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -4513,4 +4513,19 @@ class MCPServerManager:
         return [server for server in results if server is not None]
 
 
-global_mcp_server_manager: MCPServerManager = MCPServerManager()
+def _make_global_mcp_server_manager() -> MCPServerManager:
+    """Pick the egress manager: v2 (UpstreamConnection-backed) when LITELLM_USE_V2_MCP_EGRESS is
+    set, else v1. The v2 import is lazy so it can subclass MCPServerManager without an import
+    cycle, and flag-off never touches the v2 module."""
+    from litellm.proxy._experimental.mcp_server.v2_egress import v2_egress_enabled
+
+    if v2_egress_enabled():
+        from litellm.proxy._experimental.mcp_server.mcp_server_manager_v2 import (
+            MCPServerManagerV2,
+        )
+
+        return MCPServerManagerV2()
+    return MCPServerManager()
+
+
+global_mcp_server_manager: MCPServerManager = _make_global_mcp_server_manager()

litellm/proxy/_experimental/mcp_server/mcp_server_manager_v2.py

@@ -0,0 +1,20 @@
+"""v2-owned MCP egress manager (the cutover seam).
+
+``MCPServerManagerV2`` subclasses v1's ``MCPServerManager`` and, in later steps, overrides the
+per-server egress methods (``_get_tools_from_server``, ``call_tool``, the prompt/resource ops) to
+route through the v2 ``UpstreamConnection`` + ``resolve()`` instead of ``_create_mcp_client``.
+Registry, RBAC, cross-server aggregation, namespacing, and static-header resolution are inherited
+from v1 unchanged. It is injected at the composition root when ``LITELLM_USE_V2_MCP_EGRESS`` is set
+(see ``mcp_server_manager._make_global_mcp_server_manager``); flag-off keeps v1 exactly.
+
+Step 6a lands the skeleton only: no overrides, so behavior is identical to v1. The egress overrides
+land in 6b/6c.
+"""
+
+from __future__ import annotations
+
+from litellm.proxy._experimental.mcp_server.mcp_server_manager import MCPServerManager
+
+
+class MCPServerManagerV2(MCPServerManager):
+    """v2 egress manager; see the module docstring. No overrides yet (step 6a)."""

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager_v2.py

@@ -0,0 +1,27 @@
+"""Tests for the v2 egress manager factory + skeleton (step 6a)."""
+
+from litellm.proxy._experimental.mcp_server.mcp_server_manager import (
+    MCPServerManager,
+    _make_global_mcp_server_manager,
+)
+from litellm.proxy._experimental.mcp_server.mcp_server_manager_v2 import (
+    MCPServerManagerV2,
+)
+
+FLAG = "LITELLM_USE_V2_MCP_EGRESS"
+
+
+def test_v2_is_a_manager_subclass():
+    assert issubclass(MCPServerManagerV2, MCPServerManager)
+
+
+def test_factory_returns_v2_when_egress_enabled(monkeypatch):
+    monkeypatch.setenv(FLAG, "true")
+    assert isinstance(_make_global_mcp_server_manager(), MCPServerManagerV2)
+
+
+def test_factory_returns_v1_when_egress_disabled(monkeypatch):
+    monkeypatch.delenv(FLAG, raising=False)
+    manager = _make_global_mcp_server_manager()
+    assert isinstance(manager, MCPServerManager)
+    assert not isinstance(manager, MCPServerManagerV2)