fix: decouple AI completion from history save failures and improve history API errors

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/history/storage.ts

@@ -34,6 +34,22 @@ export async function saveHistoryEntry(
   return data.entry;
 }
 
+export async function saveHistoryEntrySafe(
+  entry: CalcHistoryCreate,
+): Promise<
+  { ok: true; entry: CalcHistoryEntry } | { ok: false; error: string }
+> {
+  try {
+    const saved = await saveHistoryEntry(entry);
+    return { ok: true, entry: saved };
+  } catch (err) {
+    return {
+      ok: false,
+      error: err instanceof Error ? err.message : String(err),
+    };
+  }
+}
+
 export async function deleteHistoryEntry(id: string): Promise<void> {
   const res = await fetch(`/api/history/${encodeURIComponent(id)}`, {
     method: "DELETE",