feat(batchdiff): remit rows drill to RemitDrawer

src/pages/BatchDiff.tsx

@@ -21,8 +21,10 @@ import {
   BatchDiffView,
   BatchDiffViewSkeleton,
 } from "@/components/BatchDiffView";
+import { RemitDrawer } from "@/components/RemitDrawer";
 import { useBatches } from "@/hooks/useBatches";
 import { useBatchDiff } from "@/hooks/useBatchDiff";
+import { useRemitDrawerUrlState } from "@/hooks/useRemitDrawerUrlState";
 import type { BatchSummary as ApiBatchSummary } from "@/lib/api";
 import { cn } from "@/lib/utils";
 
@@ -269,6 +271,14 @@ export function BatchDiff() {
   // BrowserRouter (production) symmetric: both update the
   // useSearchParams hook on every navigation.
   const [searchParams, setSearchParams] = useSearchParams();
+  // SP21 Phase 4 Task 4.5: mount the RemitDrawer so a deep link to
+  // /batch-diff?remit=REM-1 opens the drawer in-place. The BatchDiff
+  // data model (BatchClaimDiffSummary) is a claim-level projection —
+  // there are no per-remit IDs in the diff payload to wrap, so no
+  // click-to-drill is wired here. The drawer still mounts so the
+  // `?remit=` URL contract is honored when the user lands on this
+  // page with the param set (e.g. from an external link).
+  const { remitId, open, close } = useRemitDrawerUrlState();
   const { a, b } = useMemo(
     () => readIdsFromParams(searchParams),
     [searchParams],
@@ -835,6 +845,24 @@ export function BatchDiff() {
           <span>{ready ? "A vs B" : "awaiting picks"}</span>
         </div>
       </div>
+
+      {/* SP21 Phase 4 Task 4.5: RemitDrawer mount. There are no
+          per-remit rows in the diff payload (the page is a
+          claim-level projection), so this drawer is for deep-link
+          support only — clicking a claim row does not open it.
+          When the user lands on /batch-diff?remit=REM-1, the drawer
+          opens in-place. The `remits` list is empty so j/k is a
+          no-op while the drawer is open. */}
+      <RemitDrawer
+        remitId={remitId}
+        remits={[]}
+        onClose={close}
+        onNavigate={open}
+        onToggleHelp={() => {
+          // BatchDiff has no cheatsheet surface; `?` is a no-op
+          // here, but the prop is required by the drawer's contract.
+        }}
+      />
     </div>
   );
 }