Add position field resolution for module bays (fixes #20467)

- Add resolve_position() method to ModularComponentTemplateModel
- Update ModuleBayTemplate.instantiate() to resolve {module} in position field
- Add test_module_bay_position_resolves_placeholder test

This completes the fix for nested module placeholder issues by ensuring
the position field also resolves {module} placeholders, which is required
for building correct full paths in 3+ level hierarchies.

netbox/dcim/models/device_component_templates.py

@@ -207,6 +207,32 @@ class ModularComponentTemplateModel(ComponentTemplateModel):
             return label
         return self.label
 
+    def resolve_position(self, position, module):
+        """
+        Resolve {module} placeholder in position field.
+        
+        This is used by ModuleBayTemplate to resolve positions like "{module}/1"
+        to actual values like "A/1" when the parent module is installed in bay "A".
+        
+        Fixes Issue #20467.
+        """
+        if not position or MODULE_TOKEN not in position:
+            return position
+
+        if module:
+            modules = self._get_module_tree(module)
+            token_count = position.count(MODULE_TOKEN)
+            if token_count == 1:
+                # Single token: substitute with full path
+                full_path = '/'.join([m.module_bay.position for m in modules])
+                position = position.replace(MODULE_TOKEN, full_path, 1)
+            else:
+                # Multiple tokens: substitute level-by-level
+                for m in modules:
+                    position = position.replace(MODULE_TOKEN, m.module_bay.position, 1)
+            return position
+        return position
+
 
 class ConsolePortTemplate(ModularComponentTemplateModel):
     """
@@ -736,10 +762,11 @@ class ModuleBayTemplate(ModularComponentTemplateModel):
         verbose_name_plural = _('module bay templates')
 
     def instantiate(self, **kwargs):
+        module = kwargs.get('module')
         return self.component_model(
-            name=self.resolve_name(kwargs.get('module')),
-            label=self.resolve_label(kwargs.get('module')),
-            position=self.position,
+            name=self.resolve_name(module),
+            label=self.resolve_label(module),
+            position=self.resolve_position(self.position, module),
             **kwargs
         )
     instantiate.do_not_call_in_templates = True

netbox/dcim/tests/test_models.py

@@ -942,6 +942,83 @@ class ModuleBayTestCase(TestCase):
         self.assertEqual(interface_2.name, 'SFP 1/2')
         self.assertEqual(interface_2.label, '1/2')
 
+    def test_module_bay_position_resolves_placeholder(self):
+        """
+        Test that the position field of instantiated module bays resolves {module} placeholder.
+        
+        Issue #20467: When a module type has module bay templates with position="{module}/1",
+        the instantiated module bay should have position="A/1" (not literal "{module}/1").
+        
+        This test should:
+        - FAIL on main branch (bug present: position contains "{module}")
+        - PASS after fix (position is resolved to actual value)
+        """
+        manufacturer = Manufacturer.objects.first()
+        site = Site.objects.first()
+        device_role = DeviceRole.objects.first()
+
+        # Create device type with module bay at position 'A'
+        device_type = DeviceType.objects.create(
+            manufacturer=manufacturer,
+            model='Position Test Chassis',
+            slug='position-test-chassis'
+        )
+        ModuleBayTemplate.objects.create(
+            device_type=device_type,
+            name='Bay A',
+            position='A'
+        )
+
+        # Create module type with nested bays using {module} in POSITION field
+        extension_type = ModuleType.objects.create(
+            manufacturer=manufacturer,
+            model='Position Test Extension'
+        )
+        ModuleBayTemplate.objects.create(
+            module_type=extension_type,
+            name='Sub Bay {module}-1',
+            label='{module}-1',
+            position='{module}/1'  # This should resolve to "A/1"
+        )
+        ModuleBayTemplate.objects.create(
+            module_type=extension_type,
+            name='Sub Bay {module}-2',
+            label='{module}-2',
+            position='{module}/2'  # This should resolve to "A/2"
+        )
+
+        # Create device
+        device = Device.objects.create(
+            name='Position Test Device',
+            device_type=device_type,
+            role=device_role,
+            site=site
+        )
+
+        # Install extension module in Bay A
+        parent_bay = device.modulebays.get(name='Bay A')
+        module = Module.objects.create(
+            device=device,
+            module_bay=parent_bay,
+            module_type=extension_type
+        )
+
+        # Verify the nested bays have resolved names (this already works)
+        nested_bay_1 = module.modulebays.get(name='Sub Bay A-1')
+        nested_bay_2 = module.modulebays.get(name='Sub Bay A-2')
+        
+        # Verify labels are resolved (this already works)
+        self.assertEqual(nested_bay_1.label, 'A-1')
+        self.assertEqual(nested_bay_2.label, 'A-2')
+        
+        # Verify POSITION field is resolved (Issue #20467 - this currently fails)
+        self.assertEqual(nested_bay_1.position, 'A/1')
+        self.assertEqual(nested_bay_2.position, 'A/2')
+        
+        # Also verify no {module} literal remains
+        self.assertNotIn('{module}', nested_bay_1.position)
+        self.assertNotIn('{module}', nested_bay_2.position)
+
     def test_single_placeholder_direct_install_depth_1(self):
         """
         Test that installing a module directly at depth=1 with a single {module}