fix: Ship mermaid's own es-module dist instead of re-bundling it

mermaid is a prebuilt, minified package; running another bundler over
it produced 'undefined is not a function' at runtime. The build now
copies the dist entry and its transitive chunk imports verbatim - the
same artifact the CDN used to serve. The import closure is verified
complete at build time by construction (every referenced chunk is
copied), and the module graph import-checks cleanly under node.

Author: lfrancke

ui/build.mjs

@@ -6,10 +6,20 @@
 // built as a self-contained IIFE in its own vite pass (rollup cannot code-split
 // iife output, which is exactly what we want here).
 import { build } from 'vite';
-import { copyFileSync, cpSync, createWriteStream, mkdirSync, readdirSync, rmSync } from 'node:fs';
-import { resolve, basename } from 'node:path';
+import {
+  copyFileSync,
+  cpSync,
+  createWriteStream,
+  mkdirSync,
+  readdirSync,
+  readFileSync,
+  rmSync
+} from 'node:fs';
+import { createRequire } from 'node:module';
+import { resolve, basename, dirname } from 'node:path';
 import { ZipArchive } from 'archiver';
 
+const require = createRequire(import.meta.url);
 const root = import.meta.dirname;
 const src = resolve(root, 'src');
 const staged = resolve(root, 'build/ui');
@@ -98,25 +108,25 @@ await build(
   })
 );
 
-// mermaid is imported on demand by partials/mermaid-script.hbs and therefore
-// has to stay an es module (the classic-script entries above cannot be
-// import()ed); its internal chunks lazy-load per diagram type
-await build(
-  config({
-    build: {
-      outDir: staged,
-      emptyOutDir: false,
-      rollupOptions: {
-        input: resolve(src, 'js', 'vendor', 'mermaid.module.js'),
-        output: {
-          format: 'es',
-          entryFileNames: 'js/vendor/mermaid.js',
-          chunkFileNames: 'js/vendor/mermaid-[name]-[hash].js'
-        }
-      }
-    }
-  })
-);
+// mermaid is imported on demand by partials/mermaid-script.hbs. It ships its
+// own prebuilt es-module dist and breaks at runtime when re-bundled, so the
+// entry and its transitive chunk imports are copied verbatim instead.
+const mermaidDist = resolve(dirname(require.resolve('mermaid/package.json')), 'dist');
+const mermaidOut = resolve(staged, 'js/vendor/mermaid');
+mkdirSync(mermaidOut, { recursive: true });
+const mermaidQueue = ['mermaid.esm.min.mjs'];
+const mermaidSeen = new Set();
+while (mermaidQueue.length > 0) {
+  const file = mermaidQueue.pop();
+  if (mermaidSeen.has(file)) continue;
+  mermaidSeen.add(file);
+  const content = readFileSync(resolve(mermaidDist, file), 'utf8');
+  copyFileSync(resolve(mermaidDist, file), resolve(mermaidOut, file));
+  for (const match of content.matchAll(/(?:from\s*|import\s*\(?\s*)"\.\/([^"]+)"/g)) {
+    mermaidQueue.push(match[1]);
+  }
+}
+console.log(`mermaid: copied ${mermaidSeen.size} dist files`);
 
 for (const dir of ['helpers', 'layouts', 'partials', 'img']) {
   cpSync(resolve(src, dir), resolve(staged, dir), { recursive: true });

ui/src/js/vendor/mermaid.module.js

@@ -1,6 +1,6 @@
 <script type="module">
   if (document.querySelector('.mermaid')) {
-    const { default: mermaid } = await import('{{{uiRootPath}}}/js/vendor/mermaid.js')
+    const { default: mermaid } = await import('{{{uiRootPath}}}/js/vendor/mermaid/mermaid.esm.min.mjs')
     mermaid.initialize({ startOnLoad: true })
   }
 </script>