chore: import upstream snapshot with attribution

tools/ui/scripts/vite-plugin-relativize-base.ts

@@ -0,0 +1,61 @@
+import { readFileSync, writeFileSync, existsSync } from 'node:fs';
+import { resolve } from 'path';
+import type { Plugin } from 'vite';
+import { BUILD_CONFIG } from '../src/lib/constants/pwa';
+
+let processed = false;
+
+const OUTPUT_DIR = process.env.LLAMA_UI_OUT_DIR ?? BUILD_CONFIG.OUTPUT_DIR;
+
+function rewrite(path: string, pairs: [string, string][]): void {
+	if (!existsSync(path)) {
+		return;
+	}
+	const text = readFileSync(path, 'utf-8');
+	let out = text;
+	for (const [from, to] of pairs) {
+		out = out.split(from).join(to);
+	}
+	if (out !== text) {
+		writeFileSync(path, out, 'utf-8');
+	}
+}
+
+/**
+ * Relativize SvelteKit absolute base refs so the build is relocatable under any subpath.
+ *
+ * SvelteKit bakes root absolute /_app/ paths into the SPA fallback because paths.relative
+ * does not apply to a depth agnostic fallback page. Rewriting to ./_app/ lets a plain
+ * recursive copy of the output into /any/subdir/ resolve assets against the document URL.
+ * Runs after adapter-static writes index.html and the PWA plugin writes sw.js, deferred the
+ * same way as buildInfoPlugin so the emitted files exist.
+ */
+export function relativizeBasePlugin(): Plugin {
+	return {
+		name: 'llamacpp:relativize-base',
+		apply: 'build',
+		closeBundle() {
+			setTimeout(() => {
+				try {
+					if (processed) return;
+					processed = true;
+
+					const outDir = resolve(OUTPUT_DIR);
+
+					// index.html: modulepreload, stylesheet and bootstrap import reference "/_app/
+					rewrite(resolve(outDir, 'index.html'), [['"/_app/', '"./_app/']]);
+
+					// sw.js: the only absolute entries are the navigate fallback precache key and handler
+					rewrite(resolve(outDir, 'sw.js'), [
+						['{url:"/"', '{url:"./"'],
+						['createHandlerBoundToURL("/"', 'createHandlerBoundToURL("./"']
+					]);
+
+					console.log('Relativized base refs in index.html and sw.js');
+				} catch (error) {
+					console.error('Failed to relativize base refs:', error);
+				}
+			}, 100);
+		}
+	};
+}