refactor: relocate PRIMITIVE_NODE_CATEGORY to src/constants

Move the shared category constant to src/constants/primitiveNodes.ts so
extensions and stores import a static value without pulling the Pinia
store into extension code. Mirrors the existing pattern used by
ESSENTIALS_CATEGORY_CANONICAL in src/constants/essentialsNodes.

Drop the change-detector test that re-asserted the constant against its
literal value; the SYSTEM_NODE_DEFS contract test now compares directly
to 'utils/primitive', which is the meaningful behavioral assertion. The
tree-routing test continues to cover the runtime placement.

Addresses CodeRabbit follow-up review.

src/constants/primitiveNodes.ts

@@ -0,0 +1 @@
+export const PRIMITIVE_NODE_CATEGORY = 'utils/primitive'

src/extensions/core/widgetInputs.ts

@@ -23,6 +23,7 @@ import {
 } from '@/scripts/widgets'
 import { isPrimitiveNode } from '@/renderer/utils/nodeTypeGuards'
 import { CONFIG, GET_CONFIG } from '@/services/litegraphService'
+import { PRIMITIVE_NODE_CATEGORY } from '@/constants/primitiveNodes'
 import { mergeInputSpec } from '@/utils/nodeDefUtil'
 import { applyTextReplacements } from '@/utils/searchAndReplace'
 
@@ -624,6 +625,6 @@ app.registerExtension({
         title: 'Primitive'
       })
     )
-    PrimitiveNode.category = 'utils'
+    PrimitiveNode.category = PRIMITIVE_NODE_CATEGORY
   }
 })

src/stores/nodeDefStore.test.ts

@@ -3,7 +3,12 @@ import { setActivePinia } from 'pinia'
 import { beforeEach, describe, expect, it } from 'vitest'
 
 import type { ComfyNodeDef } from '@/schemas/nodeDefSchema'
-import { useNodeDefStore } from '@/stores/nodeDefStore'
+import {
+  ComfyNodeDefImpl,
+  SYSTEM_NODE_DEFS,
+  buildNodeDefTree,
+  useNodeDefStore
+} from '@/stores/nodeDefStore'
 import type { NodeDefFilter } from '@/stores/nodeDefStore'
 
 describe('useNodeDefStore', () => {
@@ -359,4 +364,46 @@ describe('useNodeDefStore', () => {
       expect(filterCallCount).toBe(10 * 5)
     })
   })
+
+  describe('SYSTEM_NODE_DEFS', () => {
+    it('places PrimitiveNode under the utils/primitive subcategory', () => {
+      expect(SYSTEM_NODE_DEFS.PrimitiveNode.category).toBe('utils/primitive')
+    })
+
+    it('keeps remaining frontend-only virtual nodes under the flat utils category', () => {
+      expect(SYSTEM_NODE_DEFS.Reroute.category).toBe('utils')
+      expect(SYSTEM_NODE_DEFS.Note.category).toBe('utils')
+      expect(SYSTEM_NODE_DEFS.MarkdownNote.category).toBe('utils')
+    })
+
+    it('routes PrimitiveNode into the utils/primitive branch of the node tree', () => {
+      const systemDefs = Object.values(SYSTEM_NODE_DEFS).map(
+        (def) => new ComfyNodeDefImpl(def)
+      )
+      const tree = buildNodeDefTree(systemDefs)
+
+      const utilsBranch = tree.children?.find(
+        (child) => child.label === 'utils'
+      )
+      expect(utilsBranch).toBeDefined()
+
+      const primitiveBranch = utilsBranch?.children?.find(
+        (child) => child.label === 'primitive'
+      )
+      expect(primitiveBranch).toBeDefined()
+
+      const primitiveLeaf = primitiveBranch?.children?.find(
+        (child) => child.data?.name === 'PrimitiveNode'
+      )
+      expect(primitiveLeaf).toBeDefined()
+
+      const flatUtilsLeaves =
+        utilsBranch?.children
+          ?.filter((child) => child.label !== 'primitive')
+          .map((child) => child.data?.name) ?? []
+      expect(flatUtilsLeaves).toEqual(
+        expect.arrayContaining(['Reroute', 'Note', 'MarkdownNote'])
+      )
+    })
+  })
 })

src/stores/nodeDefStore.ts

@@ -25,6 +25,7 @@ import { useSettingStore } from '@/platform/settings/settingStore'
 import { NodeSearchService } from '@/services/nodeSearchService'
 import { useSubgraphStore } from '@/stores/subgraphStore'
 import { ESSENTIALS_CATEGORY_CANONICAL } from '@/constants/essentialsNodes'
+import { PRIMITIVE_NODE_CATEGORY } from '@/constants/primitiveNodes'
 import { CORE_NODE_MODULES, getNodeSource } from '@/types/nodeSource'
 import type { NodeSource } from '@/types/nodeSource'
 import type { TreeNode } from '@/types/treeExplorerTypes'
@@ -212,7 +213,7 @@ export const SYSTEM_NODE_DEFS: Record<string, ComfyNodeDefV1> = {
   PrimitiveNode: {
     name: 'PrimitiveNode',
     display_name: 'Primitive',
-    category: 'utils',
+    category: PRIMITIVE_NODE_CATEGORY,
     input: { required: {}, optional: {} },
     output: ['*'],
     output_name: ['connect to widget input'],