Add Excalidraw MCP integration with inline diagram app rendering

[Amer-alsayed]

Motivation

• Enable the assistant to generate interactive Excalidraw diagrams from natural-language prompts by calling a local Excalidraw MCP server and embedding the returned app in chat.
• Provide a reusable, lightweight stdio MCP client and adapter so the agentic tool flow can call MCP apps the same way other tools are used.
• Improve UX by rendering MCP App payloads inline (iframe/cards) rather than forcing users to open external links.

Description

• Add a small stdio MCP JSON-RPC client api/lib/mcp-client.js to spawn MCP servers, frame/unframe Content-Length JSON-RPC, send requests/notifications and capture stderr.
• Add an Excalidraw MCP adapter api/lib/excalidraw-mcp.js that initializes MCP sessions, discovers/selects diagram tools (create_view / create_diagram fallback), calls the tool with a prompt, and normalizes returned app payloads (URL or HTML) for the frontend.
• Register a new agent tool create_excalidraw_diagram in api/lib/tools.js and wire its executor to call the Excalidraw adapter via createExcalidrawDiagram.
• Extend the agentic loop in api/chat.js to allow the new tool, instruct models to use it for diagram/flowchart requests, collect returned MCP app payloads, and emit them to clients via an SSE event mcp_app alongside sources/quality_metrics.
• Update the frontend assets/js/app.js to parse mcp_app SSE events, persist mcpApps in chat history, and render inline MCP app cards/iframes (with safe URL sanitization and srcdoc fallback).
• Add UI styles for embedded MCP app cards in assets/css/style.css and document setup/env variables in README.md (EXCALIDRAW_MCP_COMMAND, EXCALIDRAW_MCP_ARGS).

Testing

• Ran unit/integration test suite with npm test which passed (17 tests, all ok).
• Performed syntax checks with node -c on api/chat.js, api/lib/tools.js, api/lib/excalidraw-mcp.js, api/lib/mcp-client.js, and assets/js/app.js which reported no syntax errors.
• Validation steps listed in the PR body (e.g. EXCALIDRAW_MCP_COMMAND/EXCALIDRAW_MCP_ARGS configuration) were exercised during local runs; automated test suite remained green.

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Project	Deployment	Actions	Updated (UTC)
chaqgpt	Ready	Preview, Comment	Feb 19, 2026 1:22am

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