diff --git a/src/fastapi_toolsets/cli/commands/fixtures.py b/src/fastapi_toolsets/cli/commands/fixtures.py
index a782549..02b5a0a 100644
--- a/src/fastapi_toolsets/cli/commands/fixtures.py
+++ b/src/fastapi_toolsets/cli/commands/fixtures.py
@@ -72,7 +72,7 @@ async def load(
     registry = get_fixtures_registry()
     db_context = get_db_context()
 
-    context_list = [c.value for c in contexts] if contexts else [Context.BASE]
+    context_list = list(contexts) if contexts else [Context.BASE]
 
     ordered = registry.resolve_context_dependencies(*context_list)
 
diff --git a/src/fastapi_toolsets/crud/factory.py b/src/fastapi_toolsets/crud/factory.py
index 829fe47..fac3469 100644
--- a/src/fastapi_toolsets/crud/factory.py
+++ b/src/fastapi_toolsets/crud/factory.py
@@ -148,6 +148,14 @@ class AsyncCrud(Generic[ModelType]):
             return set()
         return set(cls.m2m_fields.keys())
 
+    @classmethod
+    def _resolve_facet_fields(
+        cls: type[Self],
+        facet_fields: Sequence[FacetFieldType] | None,
+    ) -> Sequence[FacetFieldType] | None:
+        """Return facet_fields if given, otherwise fall back to the class-level default."""
+        return facet_fields if facet_fields is not None else cls.facet_fields
+
     @classmethod
     def _prepare_filter_by(
         cls: type[Self],
@@ -156,10 +164,10 @@ class AsyncCrud(Generic[ModelType]):
     ) -> tuple[list[Any], list[Any]]:
         """Normalize filter_by and return (filters, joins) to apply to the query."""
         if isinstance(filter_by, BaseModel):
-            filter_by = filter_by.model_dump(exclude_none=True) or None
+            filter_by = filter_by.model_dump(exclude_none=True)
         if not filter_by:
             return [], []
-        resolved = facet_fields if facet_fields is not None else cls.facet_fields
+        resolved = cls._resolve_facet_fields(facet_fields)
         return build_filter_by(filter_by, resolved or [])
 
     @classmethod
@@ -171,15 +179,15 @@ class AsyncCrud(Generic[ModelType]):
         search_joins: list[Any],
     ) -> dict[str, list[Any]] | None:
         """Build facet filter_attributes, or return None if no facet fields configured."""
-        resolved = facet_fields if facet_fields is not None else cls.facet_fields
+        resolved = cls._resolve_facet_fields(facet_fields)
         if not resolved:
             return None
         return await build_facets(
             session,
             cls.model,
             resolved,
-            base_filters=filters or None,
-            base_joins=search_joins or None,
+            base_filters=filters,
+            base_joins=search_joins,
         )
 
     @classmethod
@@ -202,7 +210,7 @@ class AsyncCrud(Generic[ModelType]):
             ValueError: If no facet fields are configured on this CRUD class and none are
                 provided via ``facet_fields``.
         """
-        fields = facet_fields if facet_fields is not None else cls.facet_fields
+        fields = cls._resolve_facet_fields(facet_fields)
         if not fields:
             raise ValueError(
                 f"{cls.__name__} has no facet_fields configured. "
diff --git a/src/fastapi_toolsets/exceptions/handler.py b/src/fastapi_toolsets/exceptions/handler.py
index d27f2ca..1311086 100644
--- a/src/fastapi_toolsets/exceptions/handler.py
+++ b/src/fastapi_toolsets/exceptions/handler.py
@@ -10,6 +10,10 @@ from fastapi.responses import JSONResponse
 from ..schemas import ErrorResponse, ResponseStatus
 from .exceptions import ApiException
 
+_VALIDATION_LOCATION_PARAMS: frozenset[str] = frozenset(
+    {"body", "query", "path", "header", "cookie"}
+)
+
 
 def init_exceptions_handlers(app: FastAPI) -> FastAPI:
     """Register exception handlers and custom OpenAPI schema on a FastAPI app.
@@ -106,9 +110,7 @@ def _format_validation_error(
 
     for error in errors:
         field_path = ".".join(
-            str(loc)
-            for loc in error["loc"]
-            if loc not in ("body", "query", "path", "header", "cookie")
+            str(loc) for loc in error["loc"] if loc not in _VALIDATION_LOCATION_PARAMS
         )
         formatted_errors.append(
             {
diff --git a/src/fastapi_toolsets/metrics/handler.py b/src/fastapi_toolsets/metrics/handler.py
index f3374f9..1625205 100644
--- a/src/fastapi_toolsets/metrics/handler.py
+++ b/src/fastapi_toolsets/metrics/handler.py
@@ -53,17 +53,23 @@ def init_metrics(
         logger.debug("Initialising metric provider '%s'", provider.name)
         provider.func()
 
-    collectors = registry.get_collectors()
+    # Partition collectors and cache env check at startup — both are stable for the app lifetime.
+    async_collectors = [
+        c for c in registry.get_collectors() if asyncio.iscoroutinefunction(c.func)
+    ]
+    sync_collectors = [
+        c for c in registry.get_collectors() if not asyncio.iscoroutinefunction(c.func)
+    ]
+    multiprocess_mode = _is_multiprocess()
 
     @app.get(path, include_in_schema=False)
     async def metrics_endpoint() -> Response:
-        for collector in collectors:
-            if asyncio.iscoroutinefunction(collector.func):
-                await collector.func()
-            else:
-                collector.func()
+        for collector in sync_collectors:
+            collector.func()
+        for collector in async_collectors:
+            await collector.func()
 
-        if _is_multiprocess():
+        if multiprocess_mode:
             prom_registry = CollectorRegistry()
             multiprocess.MultiProcessCollector(prom_registry)
             output = generate_latest(prom_registry)