feat(batch-diff): side-by-side claim diff between two batches

src/lib/api.ts

@@ -23,6 +23,7 @@
 
 import type {
   Ack,
+  BatchDiff,
   ClaimDetail,
   ClaimOutput,
   ClaimPayment,
@@ -508,6 +509,30 @@ async function getRemittance<T = unknown>(id: string): Promise<T> {
   return (await res.json()) as T;
 }
 
+/**
+ * Fetch the side-by-side diff between two batches.
+ *
+ * Drives ``GET /api/batch-diff?a=<batch_id>&b=<batch_id>``. Both ids
+ * are required; the endpoint returns 400 when either is missing and
+ * 404 when the id is unknown — both surface here as ``ApiError`` so
+ * the page can branch on ``.status`` like every other diff / fetch
+ * surface in the app.
+ */
+async function getBatchDiff(a: string, b: string): Promise<BatchDiff> {
+  if (!isConfigured) throw notConfiguredError();
+  const res = await fetch(
+    joinUrl(
+      `/api/batch-diff?${qs({ a, b })}`,
+    ),
+    { headers: { Accept: "application/json" } },
+  );
+  if (!res.ok) {
+    const detail = await readErrorBody(res);
+    throw new ApiError(res.status, detail || res.statusText);
+  }
+  return (await res.json()) as BatchDiff;
+}
+
 async function listProviders<T = unknown>(
   params: ListProvidersParams = {}
 ): Promise<PaginatedResponse<T>> {
@@ -672,6 +697,7 @@ export const api = {
   parse999,
   listBatches,
   getBatch,
+  getBatchDiff,
   listClaims,
   getClaimDetail,
   listRemittances,