mcp(test[server]): clarify socket_name contract test runs unfiltered

``test_registered_tools_accept_socket_name`` constructs a fresh
``FastMCP("socket-name-contract")`` and asserts every registered tool
(except ``SOCKET_NAME_EXEMPT``) takes a ``socket_name`` parameter. This
exercises the unfiltered registered set, not the production singleton
at ``server.py:222`` (which has middleware + tier filtering applied
by ``run_server``).

The behavior is correct: any subset of an all-pass set is also
all-pass for the same property, so verifying on the unfiltered set
covers every tier-filtered subset by implication. Adding the scope
note to the docstring prevents a future maintainer from misreading
the test as covering the singleton — and flags that tier-specific
socket_name behavior, if ever added, would need a parallel test.

Documentation only; no test logic changes.

Author: tony

tests/test_server.py

@@ -356,6 +356,15 @@ def test_registered_tools_accept_socket_name() -> None:
     If a future tool registration drops ``socket_name``, this test
     catches the regression instead of silently making the agent-facing
     instructions a lie.
+
+    **Scope**: this test runs against an unfiltered fresh ``FastMCP`` —
+    it does NOT exercise the production singleton at ``server.py``
+    (which has middleware + ``mcp.enable(tags=..., only=True)`` applied
+    by ``run_server``). The unfiltered set is a strict superset of any
+    tier-filtered visible set, so a positive result here implies the
+    same property on every filtered subset. A future maintainer
+    adding tier-specific socket_name behavior should add a parallel
+    test against the singleton.
     """
     import asyncio
     import inspect