fix(sp25): typecheck fixups

Three small follow-ups after the live-tail triplet wired up:

  * evictOldest is now generic over (K extends string|number, V) so
    the addAck / addTa1Ack call sites don't need a type assertion.
  * Acks.test.tsx no longer spreads importOriginal() — TypeScript
    was choking on the inferred 'unknown' from the mock factory.
    Use the same ApiError / mock shape that Claims.test.tsx uses.
  * tail-stream.test.ts guards the optional gen.return() with
    so strict mode TS2722 stops complaining about possibly-undefined.

src/store/tail-store.ts

@@ -79,11 +79,11 @@ interface TailStore {
  */
 type RemitListItem = Remittance;
 
-function evictOldest<T>(
-  order: Array<string | number>,
-  dict: Record<string, T>,
+function evictOldest<K extends string | number, V>(
+  order: K[],
+  dict: Record<string, V>,
   batch: number,
-): { order: Array<string | number>; dict: Record<string, T> } {
+): { order: K[]; dict: Record<string, V> } {
   if (order.length <= TAIL_CAP) return { order, dict };
   // Drain down to the cap; never evict more than `batch` per call so a
   // 5-item overflow evicts 5, but a 1 000-item overflow evicts 100 in
@@ -93,7 +93,7 @@ function evictOldest<T>(
   const nextOrder = order.slice(toDrop);
   // Object.assign is consistently faster than `{ ...dict }` in V8 for
   // large dicts; we follow up with `delete` for each evicted id.
-  const nextDict: Record<string, T> = Object.assign({}, dict);
+  const nextDict: Record<string, V> = Object.assign({}, dict);
   for (const id of dropped) delete nextDict[String(id)];
   return { order: nextOrder, dict: nextDict };
 }
@@ -172,7 +172,7 @@ export const useTailStore = create<TailStore>((set) => ({
       const nextOrder = s.ackOrder.concat(a.id);
       if (nextOrder.length > TAIL_CAP) {
         const { order, dict } = evictOldest(nextOrder, nextAcks, EVICT_BATCH);
-        return { acks: dict, ackOrder: order as number[] };
+        return { acks: dict, ackOrder: order };
       }
       return { acks: nextAcks, ackOrder: nextOrder };
     }),
@@ -188,7 +188,7 @@ export const useTailStore = create<TailStore>((set) => ({
       const nextOrder = s.ta1AckOrder.concat(a.id);
       if (nextOrder.length > TAIL_CAP) {
         const { order, dict } = evictOldest(nextOrder, nextTa1Acks, EVICT_BATCH);
-        return { ta1Acks: dict, ta1AckOrder: order as number[] };
+        return { ta1Acks: dict, ta1AckOrder: order };
       }
       return { ta1Acks: nextTa1Acks, ta1AckOrder: nextOrder };
     }),