refactor: separate standalone Vite wiring and provider middleware

src/standalone/errors.js

@@ -0,0 +1,25 @@
+/**
+ * Extract a human-readable error message from any thrown value.
+ * Handles Error objects, strings, and plain objects with message/error fields.
+ * @param {*} error — caught exception value
+ * @returns {string} best-effort error description
+ */
+export function describeError(error) {
+  if (!error) return 'Unknown initialization error';
+  if (error instanceof Error) {
+    if (error.message && error.message.trim()) return error.message.trim();
+    return error.name || 'Initialization error';
+  }
+  if (typeof error === 'string' && error.trim()) return error.trim();
+  if (typeof error === 'object') {
+    const maybeMessage = String(error.message || error.error || '').trim();
+    if (maybeMessage) return maybeMessage;
+    try {
+      const serialized = JSON.stringify(error);
+      if (serialized && serialized !== '{}') return serialized;
+    } catch {
+      // ignore serialization error
+    }
+  }
+  return String(error);
+}