fix: guard subgraph blueprint root node

Author: huang47

src/stores/subgraphStore.test.ts

@@ -285,6 +285,26 @@ describe('useSubgraphStore', () => {
     consoleSpy.mockRestore()
   })
 
+  it('should reject blueprints without a root node', async () => {
+    const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
+    await mockFetch({
+      'empty-node.json': {
+        ...mockGraph,
+        nodes: []
+      }
+    })
+
+    const error = consoleSpy.mock.calls.find(
+      ([message]) => message === 'Failed to load subgraph blueprint'
+    )?.[1]
+    expect(error).toBeInstanceOf(TypeError)
+    expect((error as Error).message).toBe(
+      "Subgraph blueprint 'empty-node' must contain a root node"
+    )
+    expect(store.subgraphBlueprints).toHaveLength(0)
+    consoleSpy.mockRestore()
+  })
+
   it('should handle global blueprint with rejected data promise gracefully', async () => {
     const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
     await mockFetch(

src/stores/subgraphStore.ts

@@ -153,14 +153,20 @@ export const useSubgraphStore = defineStore('subgraph', () => {
       if (!force && this.isLoaded) return await super.load({ force })
       const loaded = await super.load({ force })
       const st = loaded.activeState
+      const rootNode = st.nodes[0]
+      if (!rootNode) {
+        throw new TypeError(
+          `Subgraph blueprint '${this.filename}' must contain a root node`
+        )
+      }
       const sg = (st.definitions?.subgraphs ?? []).find(
-        (sg) => sg.id == st.nodes[0].type
+        (sg) => sg.id == rootNode.type
       )
       if (!sg)
         throw new Error(
           'Loaded subgraph blueprint does not contain valid subgraph'
         )
-      sg.name = st.nodes[0].title = this.filename
+      sg.name = rootNode.title = this.filename
 
       // Copy blueprint metadata from workflow extra to subgraph extra
       // so it's available when editing via canvas.subgraph.extra
@@ -283,8 +289,12 @@ export const useSubgraphStore = defineStore('subgraph', () => {
     overrides: Partial<ComfyNodeDefV1> = {},
     name: string = workflow.filename
   ) {
-    const subgraphNode = workflow.changeTracker.initialState
-      .nodes[0] as ComfyNode
+    const subgraphNode = workflow.changeTracker.initialState.nodes[0]
+    if (!subgraphNode) {
+      throw new TypeError(
+        `Subgraph blueprint '${name}' must contain a root node`
+      )
+    }
     subgraphNode.inputs ??= []
     subgraphNode.outputs ??= []
     //NOTE: Types are cast to string. This is only used for input coloring on previews