Excalidraw Edit Permalink via JSON URL Serialization

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Summary

Generate a permalink that opens an Excalidraw document directly in the Excalidraw editor using the JSON URL format. This allows users to click a link from the Decision component and land in Excalidraw with the diagram pre-loaded for editing.

Context

Excalidraw supports encoding scene JSON into URLs that open directly in the editor. This feature would let us serialize a Polygraphs/Decision component diagram into that format and provide an "Edit in Excalidraw" link.

Acceptance Criteria

• Given a rendered graph/diagram, generate a valid Excalidraw JSON URL permalink
• Clicking the permalink opens Excalidraw with the full diagram loaded and editable
• URL encoding handles the scene elements, app state, and any embedded data

Related

• [FEAT] Generate Pugh Decision Matrix from ADRs via LLM #28 (Pugh matrix generation — matrices could also be visualized/edited this way)