fix: track main's optional serverInfo and empty-string server version

main now types Client.server_info as Implementation | None (serverInfo is
optional at 2026-07-28) and defaults server version to "" instead of None.

- ServerCard.from_server treats a derived empty version as unset, so a
  server without a version still fails card validation
- reconcile_server_card accepts server_info=None: an anonymous server makes
  no identity claim, so only the protocol version check applies

Author: claude

src/mcp/client/experimental/server_card.py

@@ -436,7 +436,7 @@ def parse_ai_catalog_response(response: httpx2.Response) -> AICatalog:
 
 def reconcile_server_card(
     card: ServerCard,
-    server_info: Implementation,
+    server_info: Implementation | None,
     *,
     protocol_version: str | None = None,
 ) -> list[CardMismatch]:
@@ -446,14 +446,17 @@ def reconcile_server_card(
     discrepancies for logging or UI. Runtime values MUST win, and cards MUST
     NOT drive security or access-control decisions. The card name matches
     when `server_info.name` equals either the full namespaced name or its
-    post-slash local part.
+    post-slash local part. A `None` `server_info` (a server that did not
+    identify itself) makes no identity claim, so only the protocol version
+    check can apply.
     """
     mismatches: list[CardMismatch] = []
-    local_name = card.name.split("/", 1)[1]
-    if server_info.name not in (card.name, local_name):
-        mismatches.append(CardMismatch(field="name", card_value=card.name, runtime_value=server_info.name))
-    if server_info.version != card.version:
-        mismatches.append(CardMismatch(field="version", card_value=card.version, runtime_value=server_info.version))
+    if server_info is not None:
+        local_name = card.name.split("/", 1)[1]
+        if server_info.name not in (card.name, local_name):
+            mismatches.append(CardMismatch(field="name", card_value=card.name, runtime_value=server_info.name))
+        if server_info.version != card.version:
+            mismatches.append(CardMismatch(field="version", card_value=card.version, runtime_value=server_info.version))
     if protocol_version is not None:
         declared = {version for remote in card.remotes or [] for version in remote.supported_protocol_versions or []}
         if declared and protocol_version not in declared:

src/mcp/shared/experimental/server_card.py

@@ -179,7 +179,9 @@ def from_server(
         resolved_icons = list(icons) if icons is not None else server.icons
         fields: dict[str, Any] = {
             "name": name,
-            "version": version if version is not None else server.version,
+            # A server signals "no version" as None or "" depending on its
+            # class; both must fail card validation rather than derive.
+            "version": version if version is not None else (server.version or None),
             "description": description if description is not None else server.description,
             "title": title if title is not None else server.title,
             "website_url": website_url if website_url is not None else server.website_url,

tests/client/experimental/test_server_card.py

@@ -922,6 +922,25 @@ def test_reconcile_reports_name_and_version_mismatches() -> None:
     )
 
 
+def test_reconcile_without_server_info_checks_only_the_protocol_version() -> None:
+    """SDK-defined: `Client.server_info` is `None` when the server did not identify
+    itself. An anonymous server makes no identity claim, so name and version cannot
+    mismatch, while a declared protocol version union still applies."""
+    assert reconcile_server_card(_card(), None) == []
+    card = ServerCard(
+        name="com.example/weather",
+        version="1.4.0",
+        description="Hourly forecasts.",
+        remotes=[
+            Remote(type="streamable-http", url="https://a.example.com/mcp", supported_protocol_versions=["2025-06-18"])
+        ],
+    )
+    mismatches = reconcile_server_card(card, None, protocol_version="2026-07-28")
+    assert [(m.field, m.card_value, m.runtime_value) for m in mismatches] == snapshot(
+        [("protocol_versions", "2025-06-18", "2026-07-28")]
+    )
+
+
 def test_reconcile_checks_the_protocol_version_against_declared_unions() -> None:
     """SDK-defined: with `protocol_version=` given, the union of every remote's declared
     `supportedProtocolVersions` is consulted. A member passes, a stranger mismatches."""