diff --git a/src/bonsai/bonsai/bim/module/cost/operator.py b/src/bonsai/bonsai/bim/module/cost/operator.py
index 61138268f0..00d5f5fec0 100644
--- a/src/bonsai/bonsai/bim/module/cost/operator.py
+++ b/src/bonsai/bonsai/bim/module/cost/operator.py
@@ -16,12 +16,15 @@
 # You should have received a copy of the GNU General Public License
 # along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
 
+# pyright: reportUnnecessaryTypeIgnoreComment=error
+
 import bpy
 import ifcopenshell.api
 import bonsai.tool as tool
 from bpy_extras.io_utils import ImportHelper
 import bonsai.tool as tool
 import bonsai.core.cost as core
+from typing import get_args, TYPE_CHECKING
 
 
 class AddCostSchedule(bpy.types.Operator, tool.Ifc.Operator):
@@ -261,9 +264,14 @@ class AssignCostItemQuantity(bpy.types.Operator, tool.Ifc.Operator):
     bl_label = "Assign Cost Item Quantity"
     bl_options = {"REGISTER", "UNDO"}
     cost_item: bpy.props.IntProperty()
-    related_object_type: bpy.props.StringProperty()
+    related_object_type: bpy.props.EnumProperty(  # type: ignore [reportRedeclaration]
+        items=[(i, i, "") for i in get_args(tool.Cost.RELATED_OBJECT_TYPE)],
+    )
     prop_name: bpy.props.StringProperty()
 
+    if TYPE_CHECKING:
+        related_object_type: tool.Cost.RELATED_OBJECT_TYPE
+
     @classmethod
     def description(cls, context, properties) -> str:
         descr = f"Assign cost item quantity to the active cost item from active {properties.related_object_type}"
@@ -708,7 +716,12 @@ class ClearCostItemAssignments(bpy.types.Operator, tool.Ifc.Operator):
     bl_label = "Clear Cost Item Product Assignments"
     bl_options = {"REGISTER", "UNDO"}
     cost_item: bpy.props.IntProperty()
-    related_object_type: bpy.props.StringProperty()
+    related_object_type: bpy.props.EnumProperty(  # type: ignore [reportRedeclaration]
+        items=[(i, i, "") for i in get_args(tool.Cost.RELATED_OBJECT_TYPE)],
+    )
+
+    if TYPE_CHECKING:
+        related_object_type: tool.Cost.RELATED_OBJECT_TYPE
 
     def _execute(self, context):
         core.clear_cost_item_assignments(
diff --git a/src/bonsai/bonsai/bim/module/sequence/operator.py b/src/bonsai/bonsai/bim/module/sequence/operator.py
index a855d8d79d..a6729a444d 100644
--- a/src/bonsai/bonsai/bim/module/sequence/operator.py
+++ b/src/bonsai/bonsai/bim/module/sequence/operator.py
@@ -16,6 +16,8 @@
 # You should have received a copy of the GNU General Public License
 # along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
 
+# pyright: reportUnnecessaryTypeIgnoreComment=error
+
 import os
 import bpy
 import json
@@ -31,6 +33,8 @@ from datetime import datetime
 from dateutil import parser, relativedelta
 from bonsai.bim.ifc import IfcStore
 from bpy_extras.io_utils import ImportHelper
+from typing import get_args, TYPE_CHECKING
+from typing_extensions import assert_never
 
 
 class EnableStatusFilters(bpy.types.Operator):
@@ -507,9 +511,14 @@ class AssignProcess(bpy.types.Operator, tool.Ifc.Operator):
     bl_label = "Assign Process"
     bl_options = {"REGISTER", "UNDO"}
     task: bpy.props.IntProperty()
-    related_object_type: bpy.props.StringProperty()
+    related_object_type: bpy.props.EnumProperty(  # type: ignore [reportRedeclaration]
+        items=[(i, i, "") for i in get_args(tool.Sequence.RELATED_OBJECT_TYPE)],
+    )
     related_object: bpy.props.IntProperty()
 
+    if TYPE_CHECKING:
+        related_object_type: tool.Sequence.RELATED_OBJECT_TYPE
+
     @classmethod
     def description(cls, context, properties):
         return f"Assign selected {properties.related_object_type} to the selected task"
@@ -530,6 +539,8 @@ class AssignProcess(bpy.types.Operator, tool.Ifc.Operator):
                 core.assign_input_products(tool.Ifc, tool.Sequence, tool.Spatial, task=tool.Ifc.get().by_id(self.task))
         elif self.related_object_type == "CONTROL":
             self.report({"ERROR"}, "Assigning process control is not yet supported")  # TODO
+        else:
+            assert_never(self.related_object_type)
 
 
 class UnassignProcess(bpy.types.Operator, tool.Ifc.Operator):
@@ -537,10 +548,15 @@ class UnassignProcess(bpy.types.Operator, tool.Ifc.Operator):
     bl_label = "Unassign Process"
     bl_options = {"REGISTER", "UNDO"}
     task: bpy.props.IntProperty()
-    related_object_type: bpy.props.StringProperty()
+    related_object_type: bpy.props.EnumProperty(  # type: ignore [reportRedeclaration]
+        items=[(i, i, "") for i in get_args(tool.Sequence.RELATED_OBJECT_TYPE)],
+    )
     related_object: bpy.props.IntProperty()
     resource: bpy.props.IntProperty()
 
+    if TYPE_CHECKING:
+        related_object_type: tool.Sequence.RELATED_OBJECT_TYPE
+
     @classmethod
     def description(cls, context, properties):
         return f"Unassign selected {properties.related_object_type} from the selected task"
@@ -570,6 +586,9 @@ class UnassignProcess(bpy.types.Operator, tool.Ifc.Operator):
                 )
         elif self.related_object_type == "CONTROL":
             pass  # TODO
+            self.report({"INFO"}, "Unassigning process control is not yet supported.")
+        else:
+            assert_never(self.related_object_type)
         return {"FINISHED"}
 
 
diff --git a/src/bonsai/bonsai/tool/resource.py b/src/bonsai/bonsai/tool/resource.py
index 45c64d3653..d3372c9afa 100644
--- a/src/bonsai/bonsai/tool/resource.py
+++ b/src/bonsai/bonsai/tool/resource.py
@@ -22,7 +22,6 @@ import bpy
 import bonsai.core.tool
 import bonsai.tool as tool
 import bonsai.bim.helper
-import bonsai.bim.module.sequence.helper as helper
 import json
 import time
 import isodate
@@ -362,6 +361,8 @@ class Resource(bonsai.core.tool.Resource):
                 )
                 time_consumed = ifcopenshell.util.resource.get_unit_consumed(productivity)
                 if time_consumed:
+                    import bonsai.bim.module.sequence.helper as helper
+
                     durations_attributes = helper.parse_duration_as_blender_props(time_consumed)
                     duration_props.years = durations_attributes["years"]
                     duration_props.months = durations_attributes["months"]
@@ -375,6 +376,8 @@ class Resource(bonsai.core.tool.Resource):
         props = bpy.context.scene.BIMResourceProductivity
         productivity = {}
         if props.quantity_consumed:
+            import bonsai.bim.module.sequence.helper as helper
+
             productivity["BaseQuantityConsumed"] = helper.blender_props_to_iso_duration(
                 props.quantity_consumed, "ELAPSEDTIME", "BaseQuantityConsumed"
             )
diff --git a/src/bonsai/bonsai/tool/sequence.py b/src/bonsai/bonsai/tool/sequence.py
index 175e588365..66fda638f1 100644
--- a/src/bonsai/bonsai/tool/sequence.py
+++ b/src/bonsai/bonsai/tool/sequence.py
@@ -32,15 +32,19 @@ import ifcopenshell.util.unit
 import bonsai.core.tool
 import bonsai.tool as tool
 import bonsai.bim.helper
-import bonsai.bim.module.sequence.helper as helper
 from dateutil import parser
 from datetime import datetime
-from typing import Optional, Any, Union
+from typing import Optional, Any, Union, Literal
 
 
 class Sequence(bonsai.core.tool.Sequence):
+
+    RELATED_OBJECT_TYPE = Literal["RESOURCE", "PRODUCT", "CONTROL"]
+
     @classmethod
     def get_work_plan_attributes(cls) -> dict[str, Any]:
+        import bonsai.bim.module.sequence.helper as helper
+
         def callback(attributes, prop):
             if "Date" in prop.name or "Time" in prop.name:
                 if prop.is_null:
@@ -87,6 +91,8 @@ class Sequence(bonsai.core.tool.Sequence):
 
     @classmethod
     def get_work_schedule_attributes(cls) -> dict[str, Any]:
+        import bonsai.bim.module.sequence.helper as helper
+
         def callback(attributes, prop):
             if "Date" in prop.name or "Time" in prop.name:
                 if prop.is_null:
@@ -336,6 +342,8 @@ class Sequence(bonsai.core.tool.Sequence):
 
     @classmethod
     def load_task_time_attributes(cls, task_time: ifcopenshell.entity_instance) -> None:
+        import bonsai.bim.module.sequence.helper as helper
+
         def callback(name, prop, data):
             if prop and prop.data_type == "string":
                 duration_props = bpy.context.scene.BIMWorkScheduleProperties.durations_attributes.add()
@@ -373,6 +381,8 @@ class Sequence(bonsai.core.tool.Sequence):
 
     @classmethod
     def get_task_time_attributes(cls) -> dict[str, Any]:
+        import bonsai.bim.module.sequence.helper as helper
+
         def callback(attributes, prop):
             if "Start" in prop.name or "Finish" in prop.name or prop.name == "StatusTime":
                 if prop.is_null:
@@ -560,6 +570,8 @@ class Sequence(bonsai.core.tool.Sequence):
 
     @classmethod
     def get_work_time_attributes(cls) -> dict[str, Any]:
+        import bonsai.bim.module.sequence.helper as helper
+
         def callback(attributes, prop):
             if "Start" in prop.name or "Finish" in prop.name:
                 if prop.is_null: