Read `category` from `definitions.subgraphs[0].category` in blueprint
JSON files as a fallback default for node categorization.
This allows blueprint authors to set the category directly in the
blueprint file without needing backend `index.json` support. The
precedence order is:
1. Explicit overrides (e.g. `info.category` from API, or `'Subgraph
Blueprints/User'` for user blueprints)
2. `definitions.subgraphs[0].category` from the blueprint JSON content
3. Bare `'Subgraph Blueprints'` fallback
Companion PR: Comfy-Org/ComfyUI#12552 (adds essential blueprints with
categories matching the Figma design)
┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9053-feat-read-category-from-blueprint-subgraph-definition-30e6d73d3650810ca23bfc5a1e97cb31)
by [Unito](https://www.unito.io)
---------
Co-authored-by: github-actions <github-actions@github.com>
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