diff --git a/demo/use_case/fastapi_auto.py b/demo/use_case/fastapi_auto.py
index 3a7351d..cf04c4f 100644
--- a/demo/use_case/fastapi_auto.py
+++ b/demo/use_case/fastapi_auto.py
@@ -38,7 +38,6 @@
     query,
 )
 
-
 # ──────────────────────────────────────────────────
 # Service with FromContext
 # ──────────────────────────────────────────────────
diff --git a/demo/use_case/mcp_server.py b/demo/use_case/mcp_server.py
index 171bf19..c3434b7 100644
--- a/demo/use_case/mcp_server.py
+++ b/demo/use_case/mcp_server.py
@@ -23,7 +23,6 @@
     UseCaseService,
     build_dto_select,
     create_use_case_mcp_server,
-    mutation,
     query,
 )
 
diff --git a/skill/template/src/main.py b/skill/template/src/main.py
index 7e57ce8..9f244f4 100644
--- a/skill/template/src/main.py
+++ b/skill/template/src/main.py
@@ -5,17 +5,17 @@
 Phase 3: + REST + MCP + Voyager with services
 """
 from contextlib import asynccontextmanager
-from typing import Any, Optional
+from typing import Any
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import HTMLResponse, PlainTextResponse
 from pydantic import BaseModel
 
-from src.db import async_session
+from sqlmodel_nexus import GraphQLHandler
 from src.database import init_db
+from src.db import async_session
 from src.models import BaseEntity
-from sqlmodel_nexus import GraphQLHandler
 
 # ── GraphQL handler ───────────────────────────────────────────────────
 
@@ -27,8 +27,8 @@
 
 # ── MCP apps (must be created before lifespan to combine lifespans) ───
 
-from sqlmodel_nexus.mcp import create_mcp_server  # noqa: E402
 from sqlmodel_nexus import UseCaseAppConfig, create_use_case_mcp_server  # noqa: E402
+from sqlmodel_nexus.mcp import create_mcp_server  # noqa: E402
 from src.models import er  # noqa: E402
 from src.service.sprint.service import SprintService  # noqa: E402
 from src.service.task.service import TaskService  # noqa: E402
@@ -101,8 +101,8 @@ async def lifespan(app: FastAPI):
 
 class GraphQLRequest(BaseModel):
     query: str
-    variables: Optional[dict[str, Any]] = None
-    operation_name: Optional[str] = None
+    variables: dict[str, Any] | None = None
+    operation_name: str | None = None
 
 
 @app.get("/graphql", response_class=HTMLResponse)
diff --git a/skill/template/src/models.py b/skill/template/src/models.py
index 235bf38..3cb0ae2 100644
--- a/skill/template/src/models.py
+++ b/skill/template/src/models.py
@@ -11,7 +11,6 @@
 from sqlmodel import Field, Relationship, SQLModel, select
 
 from sqlmodel_nexus import mutation, query
-
 from src.db import async_session
 
 
diff --git a/skill/template/src/service/sprint/dtos.py b/skill/template/src/service/sprint/dtos.py
index 15f8e1a..82f8324 100644
--- a/skill/template/src/service/sprint/dtos.py
+++ b/skill/template/src/service/sprint/dtos.py
@@ -1,6 +1,5 @@
 """Sprint-related DTOs — SprintSummary with derived fields."""
 from sqlmodel_nexus import DefineSubset, SubsetConfig
-
 from src.models import Sprint
 from src.service.task.dtos import TaskSummary
 
diff --git a/skill/template/src/service/sprint/service.py b/skill/template/src/service/sprint/service.py
index 5c256cf..071c36d 100644
--- a/skill/template/src/service/sprint/service.py
+++ b/skill/template/src/service/sprint/service.py
@@ -1,6 +1,5 @@
 """Sprint UseCaseService — sprint management with task statistics."""
 from sqlmodel_nexus import UseCaseService, build_dto_select, query
-
 from src.database import async_session
 from src.models import Resolver, Sprint
 from src.service.sprint.dtos import SprintSummary
diff --git a/skill/template/src/service/task/dtos.py b/skill/template/src/service/task/dtos.py
index 0e17863..ff70c3c 100644
--- a/skill/template/src/service/task/dtos.py
+++ b/skill/template/src/service/task/dtos.py
@@ -1,6 +1,5 @@
 """Task-related DTOs — UserSummary, TaskSummary."""
 from sqlmodel_nexus import DefineSubset, SubsetConfig
-
 from src.models import Task, User
 
 
diff --git a/skill/template/src/service/task/service.py b/skill/template/src/service/task/service.py
index 9045563..84ed3c5 100644
--- a/skill/template/src/service/task/service.py
+++ b/skill/template/src/service/task/service.py
@@ -1,6 +1,5 @@
 """Task UseCaseService — task management with auto-loaded owner."""
 from sqlmodel_nexus import UseCaseService, build_dto_select, query
-
 from src.database import async_session
 from src.models import Resolver, Task
 from src.service.task.dtos import TaskSummary
diff --git a/src/sqlmodel_nexus/voyager/type_helper.py b/src/sqlmodel_nexus/voyager/type_helper.py
index 3079731..0c10c9e 100644
--- a/src/sqlmodel_nexus/voyager/type_helper.py
+++ b/src/sqlmodel_nexus/voyager/type_helper.py
@@ -285,17 +285,22 @@ def safe_issubclass(kls, target_kls):
         return False
 
 
-def update_forward_refs(kls):
+def update_forward_refs(kls, _visited: set | None = None):
     """Recursively update forward references in Pydantic models."""
+    if _visited is None:
+        _visited = set()
     for shelled_type in get_core_types(kls):
         if safe_issubclass(shelled_type, BaseModel):
+            if shelled_type in _visited:
+                continue
+            _visited.add(shelled_type)
             try:
                 shelled_type.model_rebuild()
             except Exception:
                 pass
             # Recurse into fields
             for field in shelled_type.model_fields.values():
-                update_forward_refs(field.annotation)
+                update_forward_refs(field.annotation, _visited)
 
 
 def is_generic_container(cls):
diff --git a/src/sqlmodel_nexus/voyager/voyager_context.py b/src/sqlmodel_nexus/voyager/voyager_context.py
index 5b0369d..1c6d47d 100644
--- a/src/sqlmodel_nexus/voyager/voyager_context.py
+++ b/src/sqlmodel_nexus/voyager/voyager_context.py
@@ -8,6 +8,7 @@
 from pathlib import Path
 
 from sqlmodel_nexus.loader.registry import ErManager
+from sqlmodel_nexus.use_case.business import UseCaseService
 from sqlmodel_nexus.voyager.er_diagram_dot import ErDiagramDotBuilder
 from sqlmodel_nexus.voyager.render import Renderer
 from sqlmodel_nexus.voyager.render_style import DEFAULT_PRIMARY
diff --git a/tests/test_argument_types.py b/tests/test_argument_types.py
index abbd76f..45fa6dd 100644
--- a/tests/test_argument_types.py
+++ b/tests/test_argument_types.py
@@ -98,7 +98,7 @@ async def get_filtered(cls, limit: int):
         registry = ErManager(entities=entities, session_factory=session_factory)
         executor = QueryExecutor(registry)
 
-        method = getattr(UserQuery, "get_filtered")
+        method = UserQuery.get_filtered
         query_methods = {"userGetFiltered": (FixtureUser, method)}
         parsed = QueryParser().parse("{ userGetFiltered(limit: 1) { id name } }")
 
diff --git a/tests/test_introspection.py b/tests/test_introspection.py
index 0214b01..6e2c5a0 100644
--- a/tests/test_introspection.py
+++ b/tests/test_introspection.py
@@ -61,7 +61,7 @@ def create_config(
         score: float = 1.0,
         is_active: bool = True,
         tag: str | None = None,
-        tags: list[str] = [],
+        tags: list[str] | None = None,
     ) -> "IntrospectionConfig":
         return cls(key=key, value=value)
 
@@ -697,12 +697,12 @@ def test_bool_false_default_format(self, generator: IntrospectionGenerator):
         assert enabled_arg["defaultValue"] != "False"
 
     def test_list_default_format(self, generator: IntrospectionGenerator):
-        """List defaults must be valid GraphQL list literals."""
+        """Optional list with None default renders as null in GraphQL."""
         schema = generator.generate()
         field = self._get_mutation_field(schema, "introspectionConfigCreateConfig")
         tags_arg = next(a for a in field["args"] if a["name"] == "tags")
 
-        assert tags_arg["defaultValue"] == "[]"
+        assert tags_arg["defaultValue"] == "null"
 
     def test_build_client_schema_succeeds(self, generator: IntrospectionGenerator):
         """Full introspection result must be consumable by graphql build_client_schema.
diff --git a/tests/test_voyager_selfref.py b/tests/test_voyager_selfref.py
index 62934d8..0c1e45e 100644
--- a/tests/test_voyager_selfref.py
+++ b/tests/test_voyager_selfref.py
@@ -9,16 +9,17 @@
     3. Pass the DTO as a UseCaseService return type
     4. Access Voyager endpoint → triggers update_forward_refs → RecursionError
 
-Root cause: `update_forward_refs` has no visited-set, so self-referencing types
-cause unbounded recursion through field annotations.
+Root cause: `update_forward_refs` had no visited-set, so self-referencing types
+caused unbounded recursion through field annotations.
+
+Fix: Added a `_visited` set parameter to track already-processed types and
+skip them on re-encounter, breaking the recursion cycle.
 """
 from sqlmodel import Field, SQLModel
 
-import pytest
 from sqlmodel_nexus import DefineSubset, SubsetConfig
 from sqlmodel_nexus.voyager.type_helper import update_forward_refs
 
-
 # ── Minimal self-referencing setup ─────────────────────────────────────
 
 
@@ -37,10 +38,8 @@ class CommentDTO(DefineSubset):
 
 
 class TestVoyagerSelfReference:
-    def test_update_forward_refs_on_self_referencing_dto_raises_recursion(self):
-        """Directly calling update_forward_refs on a self-referencing DTO
-        triggers RecursionError. This documents the known bug — the fix
-        should add a visited-set to prevent re-processing seen types."""
+    def test_update_forward_refs_on_self_referencing_dto_completes(self):
+        """update_forward_refs should handle self-referencing DTOs
+        without RecursionError by using a visited-set to avoid cycles."""
 
-        with pytest.raises(RecursionError):
-            update_forward_refs(CommentDTO)
+        update_forward_refs(CommentDTO)  # should not raise