fix(wizard): retry createDraft on 500/502/503/504 + human error message

POST /api/ea2/flow currently returns 500 after 19s on demo upstream.
Retry once with backoff, then surface a clear 'EA2 backend temporarily
unable to create new processes' message naming the status. The user
gets actionable info instead of a raw 500.

src/lib/wizardApi.ts

@@ -67,17 +67,31 @@ function authHeaders(): Record<string, string> {
 
 export const wizardApi = {
   async createDraft(payload: CreateDraftPayload, signal?: AbortSignal) {
-    const res = await fetch(`${api.config.baseUrl}/api/ea2/flow`, {
-      method: "POST",
-      headers: authHeaders(),
-      body: JSON.stringify({ kind: "definition", status: "draft", ...payload }),
-      signal,
-    });
-    if (!res.ok) {
-      const detail = await res.text().catch(() => "");
-      throw new Error(`createDraft ${res.status}: ${detail.slice(0, 200)}`);
+    const body = JSON.stringify({ kind: "definition", status: "draft", ...payload });
+    const transient = new Set([500, 502, 503, 504]);
+    let lastDetail = "";
+    let lastStatus = 0;
+    for (let attempt = 0; attempt < 2; attempt++) {
+      try {
+        const res = await fetch(`${api.config.baseUrl}/api/ea2/flow`, {
+          method: "POST",
+          headers: authHeaders(),
+          body,
+          signal,
+        });
+        if (res.ok) return await res.json() as { _key: string; name: string };
+        lastStatus = res.status;
+        lastDetail = await res.text().catch(() => "");
+        if (!transient.has(res.status)) break;
+      } catch (e) {
+        lastDetail = (e as Error).message;
+      }
+      await new Promise((r) => setTimeout(r, 600 * (attempt + 1)));
     }
-    return res.json() as Promise<{ _key: string; name: string }>;
+    if (transient.has(lastStatus)) {
+      throw new Error(`The EA2 backend is temporarily unable to create new processes (status ${lastStatus}). Try again in a moment, or report this if it keeps happening.`);
+    }
+    throw new Error(`createDraft ${lastStatus}: ${lastDetail.slice(0, 200)}`);
   },
 
   async updateDraftConfig(key: string, patch: Record<string, any>, signal?: AbortSignal) {