feat: integrate excalidraw MCP into bootstrap and runtime setup

- install.sh: run mosaic-ensure-excalidraw post-install (non-fatal)
- runtime-setup.ts: configure excalidraw MCP during wizard setup
- bin/mosaic-ensure-excalidraw: install deps + register MCP with Claude
- runtime/mcp/EXCALIDRAW.json: MCP server config template
- tools/excalidraw/: headless .excalidraw → SVG export server

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/excalidraw/.gitignore

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+node_modules/

tools/excalidraw/launch.sh

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+#!/usr/bin/env bash
+# Launcher for Excalidraw MCP stdio server.
+set -euo pipefail
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+exec node --loader "$SCRIPT_DIR/loader.mjs" "$SCRIPT_DIR/server.mjs"

tools/excalidraw/loader.mjs

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+/**
+ * Custom ESM loader to fix missing .js extensions in @excalidraw/excalidraw deps.
+ *
+ * Problems patched:
+ * 1. excalidraw imports 'roughjs/bin/rough' (and other roughjs/* paths) without .js
+ * 2. roughjs/* files import sibling modules as './canvas' (relative, no .js)
+ * 3. JSON files need { type: 'json' } import attribute in Node.js v22+
+ *
+ * Usage: node --loader ./loader.mjs server.mjs [args...]
+ */
+
+import { fileURLToPath, pathToFileURL } from 'url';
+import { dirname, resolve as pathResolve } from 'path';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+// Modules that have incompatible ESM format — redirect to local stubs
+const STUBS = {
+  '@excalidraw/laser-pointer': pathToFileURL(pathResolve(__dirname, 'stubs/laser-pointer.mjs')).href,
+};
+
+export async function resolve(specifier, context, nextResolve) {
+  // 0. Module stubs (incompatible ESM format packages)
+  if (STUBS[specifier]) {
+    return { url: STUBS[specifier], shortCircuit: true };
+  }
+
+  // 1. Bare roughjs/* specifiers without .js extension
+  if (/^roughjs\/bin\/[a-z-]+$/.test(specifier)) {
+    return nextResolve(`${specifier}.js`, context);
+  }
+
+  // 2. Relative imports without extension (e.g. './canvas' from roughjs/bin/rough.js)
+  //    These come in as relative paths that resolve to extensionless file URLs.
+  if (specifier.startsWith('./') || specifier.startsWith('../')) {
+    // Try resolving first; if it fails with a missing-extension error, add .js
+    try {
+      return await nextResolve(specifier, context);
+    } catch (err) {
+      if (err.code === 'ERR_MODULE_NOT_FOUND') {
+        // Try appending .js
+        try {
+          return await nextResolve(`${specifier}.js`, context);
+        } catch {
+          // Fall through to original error
+        }
+      }
+      throw err;
+    }
+  }
+
+  // 3. JSON imports need type: 'json' attribute
+  if (specifier.endsWith('.json')) {
+    const resolved = await nextResolve(specifier, context);
+    if (!resolved.importAttributes?.type) {
+      return {
+        ...resolved,
+        importAttributes: { ...resolved.importAttributes, type: 'json' },
+      };
+    }
+    return resolved;
+  }
+
+  return nextResolve(specifier, context);
+}
+
+export async function load(url, context, nextLoad) {
+  // Ensure JSON files are loaded with json format
+  if (url.endsWith('.json')) {
+    return nextLoad(url, {
+      ...context,
+      importAttributes: { ...context.importAttributes, type: 'json' },
+    });
+  }
+  return nextLoad(url, context);
+}

tools/excalidraw/package.json

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+{
+  "name": "excalidraw-mcp",
+  "version": "1.0.0",
+  "type": "module",
+  "private": true,
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.12.0",
+    "@excalidraw/excalidraw": "^0.18.0",
+    "jsdom": "^25.0.1"
+  }
+}

tools/excalidraw/server.mjs

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+#!/usr/bin/env node
+/**
+ * Excalidraw MCP stdio server
+ * Provides headless .excalidraw → SVG export via @excalidraw/excalidraw.
+ * Optional: diagram generation via EXCALIDRAW_GEN_PATH (excalidraw_gen.py).
+ */
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
+import { z } from "zod/v3";
+import { readFileSync, writeFileSync, existsSync } from 'fs';
+import { resolve } from 'path';
+import { spawnSync } from 'child_process';
+import { JSDOM } from 'jsdom';
+
+// ---------------------------------------------------------------------------
+// 1. DOM environment — must be established BEFORE importing excalidraw
+// ---------------------------------------------------------------------------
+
+const dom = new JSDOM('<!DOCTYPE html><html><body></body></html>', {
+  url: 'http://localhost/',
+  pretendToBeVisual: true,
+});
+
+const { window } = dom;
+
+// Helper: define a global, overriding read-only getters (e.g. navigator in Node v22)
+function defineGlobal(key, value) {
+  if (value === undefined) return;
+  try {
+    Object.defineProperty(global, key, {
+      value,
+      writable: true,
+      configurable: true,
+    });
+  } catch {
+    // Already defined and non-configurable — skip
+  }
+}
+
+// Core DOM globals
+defineGlobal('window',    window);
+defineGlobal('document',  window.document);
+defineGlobal('navigator', window.navigator);
+defineGlobal('location',  window.location);
+defineGlobal('history',   window.history);
+defineGlobal('screen',    window.screen);
+
+// Element / event interfaces
+for (const key of [
+  'Node', 'Element', 'HTMLElement', 'SVGElement', 'SVGSVGElement',
+  'HTMLCanvasElement', 'HTMLImageElement', 'Image',
+  'Event', 'CustomEvent', 'MouseEvent', 'PointerEvent',
+  'KeyboardEvent', 'TouchEvent', 'WheelEvent', 'InputEvent',
+  'MutationObserver', 'ResizeObserver', 'IntersectionObserver',
+  'XMLHttpRequest', 'XMLSerializer',
+  'DOMParser', 'Range',
+  'getComputedStyle', 'matchMedia',
+]) {
+  defineGlobal(key, window[key]);
+}
+
+// Animation frame stubs (jsdom doesn't implement them)
+global.requestAnimationFrame  = (fn) => setTimeout(() => fn(Date.now()), 0);
+global.cancelAnimationFrame   = (id) => clearTimeout(id);
+
+// CSS Font Loading API stub — jsdom doesn't implement FontFace
+class FontFaceStub {
+  constructor(family, source, _descriptors) {
+    this.family = family;
+    this.source = source;
+    this.status = 'loaded';
+    this.loaded = Promise.resolve(this);
+  }
+  load() { return Promise.resolve(this); }
+}
+defineGlobal('FontFace', FontFaceStub);
+
+// FontFaceSet stub for document.fonts
+const fontFaceSet = {
+  add: () => {},
+  delete: () => {},
+  has: () => false,
+  clear: () => {},
+  load: () => Promise.resolve([]),
+  check: () => true,
+  ready: Promise.resolve(),
+  status: 'loaded',
+  forEach: () => {},
+  [Symbol.iterator]: function*() {},
+};
+Object.defineProperty(window.document, 'fonts', {
+  value: fontFaceSet,
+  writable: true,
+  configurable: true,
+});
+
+// Canvas stub — excalidraw's exportToSvg doesn't need real canvas rendering,
+// but the class must exist for isinstance checks.
+if (!global.HTMLCanvasElement) {
+  defineGlobal('HTMLCanvasElement', window.HTMLCanvasElement ?? class HTMLCanvasElement {});
+}
+
+// Device pixel ratio
+global.devicePixelRatio = 1;
+
+// ---------------------------------------------------------------------------
+// 1b. Stub canvas getContext — excalidraw calls this at module init time.
+//     jsdom throws "Not implemented" by default; we return a no-op 2D stub.
+// ---------------------------------------------------------------------------
+
+const _canvasCtx = {
+  canvas: { width: 800, height: 600 },
+  fillRect: () => {}, clearRect: () => {}, strokeRect: () => {},
+  getImageData: (x, y, w, h) => ({ data: new Uint8ClampedArray(w * h * 4), width: w, height: h }),
+  putImageData: () => {}, createImageData: () => ({ data: new Uint8ClampedArray(0) }),
+  setTransform: () => {}, resetTransform: () => {}, transform: () => {},
+  drawImage: () => {}, save: () => {}, restore: () => {},
+  scale: () => {}, rotate: () => {}, translate: () => {},
+  beginPath: () => {}, closePath: () => {}, moveTo: () => {}, lineTo: () => {},
+  bezierCurveTo: () => {}, quadraticCurveTo: () => {},
+  arc: () => {}, arcTo: () => {}, ellipse: () => {}, rect: () => {},
+  fill: () => {}, stroke: () => {}, clip: () => {},
+  fillText: () => {}, strokeText: () => {},
+  measureText: (t) => ({ width: t.length * 8, actualBoundingBoxAscent: 12, actualBoundingBoxDescent: 3, fontBoundingBoxAscent: 14, fontBoundingBoxDescent: 4 }),
+  createLinearGradient: () => ({ addColorStop: () => {} }),
+  createRadialGradient: () => ({ addColorStop: () => {} }),
+  createPattern: () => null,
+  setLineDash: () => {}, getLineDash: () => [],
+  isPointInPath: () => false, isPointInStroke: () => false,
+  getContextAttributes: () => ({ alpha: true, desynchronized: false }),
+  font: '10px sans-serif', fillStyle: '#000', strokeStyle: '#000',
+  lineWidth: 1, lineCap: 'butt', lineJoin: 'miter',
+  textAlign: 'start', textBaseline: 'alphabetic',
+  globalAlpha: 1, globalCompositeOperation: 'source-over',
+  shadowOffsetX: 0, shadowOffsetY: 0, shadowBlur: 0, shadowColor: 'transparent',
+  miterLimit: 10, lineDashOffset: 0, filter: 'none', imageSmoothingEnabled: true,
+};
+
+// Patch before excalidraw import so module-level canvas calls get the stub
+if (window.HTMLCanvasElement) {
+  window.HTMLCanvasElement.prototype.getContext = function (type) {
+    if (type === '2d') return _canvasCtx;
+    return null;
+  };
+}
+
+// ---------------------------------------------------------------------------
+// 2. Load excalidraw (dynamic import so globals are set first)
+// ---------------------------------------------------------------------------
+
+let exportToSvg;
+try {
+  const excalidraw = await import('@excalidraw/excalidraw');
+  exportToSvg = excalidraw.exportToSvg;
+  if (!exportToSvg) throw new Error('exportToSvg not found in package exports');
+} catch (err) {
+  process.stderr.write(`FATAL: Failed to load @excalidraw/excalidraw: ${err.message}\n`);
+  process.exit(1);
+}
+
+// ---------------------------------------------------------------------------
+// 3. SVG export helper
+// ---------------------------------------------------------------------------
+
+async function renderToSvg(elements, appState, files) {
+  const svgEl = await exportToSvg({
+    elements: elements ?? [],
+    appState: {
+      exportWithDarkMode: false,
+      exportBackground: true,
+      viewBackgroundColor: '#ffffff',
+      ...appState,
+    },
+    files: files ?? {},
+  });
+  const serializer = new window.XMLSerializer();
+  return serializer.serializeToString(svgEl);
+}
+
+// ---------------------------------------------------------------------------
+// 4. Gen subprocess helper (optional — requires EXCALIDRAW_GEN_PATH)
+// ---------------------------------------------------------------------------
+
+function requireGenPath() {
+  const p = process.env.EXCALIDRAW_GEN_PATH;
+  if (!p) {
+    return null;
+  }
+  return p;
+}
+
+function spawnGen(args) {
+  const genPath = requireGenPath();
+  if (!genPath) {
+    return {
+      ok: false,
+      text: 'EXCALIDRAW_GEN_PATH is not set. Set it to the path of excalidraw_gen.py to use diagram generation.',
+    };
+  }
+  const result = spawnSync('python3', [genPath, ...args], { encoding: 'utf8' });
+  if (result.error) return { ok: false, text: `spawn error: ${result.error.message}` };
+  if (result.status !== 0) return { ok: false, text: result.stderr || 'subprocess failed' };
+  return { ok: true, text: result.stdout.trim() };
+}
+
+// ---------------------------------------------------------------------------
+// 5. MCP Server
+// ---------------------------------------------------------------------------
+
+const server = new McpServer({
+  name: "excalidraw",
+  version: "1.0.0",
+});
+
+// --- Tool: excalidraw_to_svg ---
+
+server.tool(
+  "excalidraw_to_svg",
+  "Convert Excalidraw elements JSON to SVG string",
+  {
+    elements: z.string().describe("JSON string of Excalidraw elements array"),
+    app_state: z.string().optional().describe("JSON string of appState overrides"),
+  },
+  async ({ elements, app_state }) => {
+    let parsed;
+    try {
+      parsed = JSON.parse(elements);
+    } catch (err) {
+      throw new Error(`Invalid elements JSON: ${err.message}`);
+    }
+    const appState = app_state ? JSON.parse(app_state) : {};
+    const svg = await renderToSvg(parsed, appState, {});
+    return { content: [{ type: "text", text: svg }] };
+  }
+);
+
+// --- Tool: excalidraw_file_to_svg ---
+
+server.tool(
+  "excalidraw_file_to_svg",
+  "Convert an .excalidraw file to SVG (writes .svg alongside the input file)",
+  {
+    file_path: z.string().describe("Absolute or relative path to .excalidraw file"),
+  },
+  async ({ file_path }) => {
+    const absPath = resolve(file_path);
+    if (!existsSync(absPath)) {
+      throw new Error(`File not found: ${absPath}`);
+    }
+    const raw = JSON.parse(readFileSync(absPath, 'utf8'));
+    const svg = await renderToSvg(raw.elements, raw.appState, raw.files);
+    const outPath = absPath.replace(/\.excalidraw$/, '.svg');
+    writeFileSync(outPath, svg, 'utf8');
+    return {
+      content: [{ type: "text", text: `SVG written to: ${outPath}\n\n${svg}` }],
+    };
+  }
+);
+
+// --- Tool: list_diagrams ---
+
+server.tool(
+  "list_diagrams",
+  "List available diagram templates from the DIAGRAMS registry (requires EXCALIDRAW_GEN_PATH)",
+  {},
+  async () => {
+    const res = spawnGen(['--list']);
+    return { content: [{ type: "text", text: res.text }] };
+  }
+);
+
+// --- Tool: generate_diagram ---
+
+server.tool(
+  "generate_diagram",
+  "Generate an .excalidraw file from a named diagram template (requires EXCALIDRAW_GEN_PATH)",
+  {
+    name: z.string().describe("Diagram template name (from list_diagrams)"),
+    output_path: z.string().optional().describe("Output path for the .excalidraw file"),
+  },
+  async ({ name, output_path }) => {
+    const args = [name];
+    if (output_path) args.push('--output', output_path);
+    const res = spawnGen(args);
+    if (!res.ok) throw new Error(res.text);
+    return { content: [{ type: "text", text: res.text }] };
+  }
+);
+
+// --- Tool: generate_and_export ---
+
+server.tool(
+  "generate_and_export",
+  "Generate an .excalidraw file and immediately export it to SVG (requires EXCALIDRAW_GEN_PATH)",
+  {
+    name: z.string().describe("Diagram template name (from list_diagrams)"),
+    output_path: z.string().optional().describe("Output path for the .excalidraw file (SVG written alongside)"),
+  },
+  async ({ name, output_path }) => {
+    const genArgs = [name];
+    if (output_path) genArgs.push('--output', output_path);
+    const genRes = spawnGen(genArgs);
+    if (!genRes.ok) throw new Error(genRes.text);
+
+    const excalidrawPath = genRes.text;
+    if (!existsSync(excalidrawPath)) {
+      throw new Error(`Generated file not found: ${excalidrawPath}`);
+    }
+
+    const raw = JSON.parse(readFileSync(excalidrawPath, 'utf8'));
+    const svg = await renderToSvg(raw.elements, raw.appState, raw.files);
+    const svgPath = excalidrawPath.replace(/\.excalidraw$/, '.svg');
+    writeFileSync(svgPath, svg, 'utf8');
+
+    return {
+      content: [{ type: "text", text: `Generated: ${excalidrawPath}\nExported SVG: ${svgPath}` }],
+    };
+  }
+);
+
+// --- Start ---
+const transport = new StdioServerTransport();
+await server.connect(transport);

tools/excalidraw/stubs/laser-pointer.mjs

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+/**
+ * Stub for @excalidraw/laser-pointer
+ * The real package uses a Parcel bundle format that Node.js ESM can't consume.
+ * For headless SVG export, the laser pointer feature is not needed.
+ */
+export class LaserPointer {}
+export default { LaserPointer };