fix(mcp): normalize paginateAll empty results to non-nil slice

Author: Copilot

internal/mcp/pagination.go

@@ -80,6 +80,9 @@ func paginateAll[T any](
 	if err != nil {
 		return nil, fmt.Errorf("list%s: backend serverID=%s: %w", itemKind, serverID, err)
 	}
+	if result == nil {
+		result = []T{}
+	}
 	logConn.Printf("list%s: received %d %s total from serverID=%s", itemKind, len(result), itemKind, serverID)
 	return result, nil
 }

internal/mcp/pagination_test.go

@@ -246,6 +246,7 @@ func TestPaginateAllHelper(t *testing.T) {
 		items, err := paginateAll("server1", "Tools", fetch)
 
 		require.NoError(t, err)
+		assert.NotNil(t, items)
 		assert.Empty(t, items)
 	})