feat: support custom descriptions for subgraph tooltips (#9003)

## Summary

Adds support for custom descriptions on subgraph nodes that display as
tooltips when hovering.

## Changes

- Add optional `description` field to `ExportedSubgraph` interface and
`Subgraph` class
- Use description with fallback to default string in
`subgraphService.createNodeDef()`
- Add `description` to `SubgraphDefinitionBase` interface and Zod schema
for validation

## Review Focus

- Backwards compatibility: undefined description falls back to `Subgraph
node for ${name}`
- Serialization pattern: conditional spread `...(this.description && {
description })`

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9003-feat-support-custom-descriptions-for-subgraph-tooltips-30d6d73d36508129bd75c77eb1c31cfb)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/LGraph.ts

@@ -2657,6 +2657,8 @@ export class Subgraph
 
   /** The display name of the subgraph. */
   name: string = 'Unnamed Subgraph'
+  /** Optional description shown as tooltip when hovering over the subgraph node. */
+  description?: string
 
   readonly inputNode = new SubgraphInputNode(this)
   readonly outputNode = new SubgraphOutputNode(this)
@@ -2707,9 +2709,10 @@ export class Subgraph
       | (ISerialisedGraph & ExportedSubgraph)
       | (SerialisableGraph & ExportedSubgraph)
   ): void {
-    const { name, inputs, outputs, widgets } = data
+    const { name, description, inputs, outputs, widgets } = data
 
     this.name = name
+    this.description = description
     if (inputs) {
       this.inputs.length = 0
       for (const input of inputs) {
@@ -2920,6 +2923,7 @@ export class Subgraph
       revision: this.revision,
       config: this.config,
       name: this.name,
+      ...(this.description && { description: this.description }),
       inputNode: this.inputNode.asSerialisable(),
       outputNode: this.outputNode.asSerialisable(),
       inputs: this.inputs.map((x) => x.asSerialisable()),

src/lib/litegraph/src/subgraph/SubgraphSerialization.test.ts

@@ -76,7 +76,6 @@ describe.skip('SubgraphSerialization - Basic Serialization', () => {
     // Verify core properties
     expect(restored.id).toBe(original.id)
     expect(restored.name).toBe(original.name)
-    // @ts-expect-error description property not in type definition
     expect(restored.description).toBe(original.description)
 
     // Verify I/O structure

src/lib/litegraph/src/types/serialisation.ts

@@ -139,6 +139,8 @@ export interface ExportedSubgraph extends SerialisableGraph {
   name: string
   /** Optional category for organizing subgraph blueprints in the node library. */
   category?: string
+  /** Optional description shown as tooltip when hovering over the subgraph node. */
+  description?: string
   inputNode: ExportedSubgraphIONode
   outputNode: ExportedSubgraphIONode
   /** Ordered list of inputs to the subgraph itself. Similar to a reroute, with the input side in the graph, and the output side in the subgraph. */

src/platform/workflow/validation/schemas/workflowSchema.ts

@@ -396,6 +396,8 @@ interface SubgraphDefinitionBase<
   id: string
   revision: number
   name: string
+  /** Optional description shown as tooltip when hovering over the subgraph node. */
+  description?: string
   category?: string
   /** Custom metadata for the subgraph (description, searchAliases, etc.) */
   extra?: T extends ComfyWorkflow1BaseInput
@@ -432,6 +434,8 @@ const zSubgraphDefinition = zComfyWorkflow1
     id: z.string().uuid(),
     revision: z.number(),
     name: z.string(),
+    /** Optional description shown as tooltip when hovering over the subgraph node. */
+    description: z.string().optional(),
     category: z.string().optional(),
     inputNode: zExportedSubgraphIONode,
     outputNode: zExportedSubgraphIONode,

src/services/subgraphService.ts

@@ -49,7 +49,7 @@ export const useSubgraphService = () => {
       output_tooltips: [],
       name: id,
       display_name: name,
-      description: `Subgraph node for ${name}`,
+      description: exportedSubgraph.description || `Subgraph node for ${name}`,
       category: 'subgraph',
       output_node: false,
       python_module: 'nodes'