feat(sp8): frontend — resubmit ZIP download UX

Wire the new ``?download=true`` resubmit endpoint into the Inbox
page. Operators can now ask the backend for a ZIP of regenerated
837s straight from the rejected-claims bulk action, with the
``X-Cyclone-Serialize-Errors`` header surfaced as a non-blocking
warning so partial successes don't swallow per-claim failures.

  * ``src/lib/inbox-api.ts``: new ``resubmitRejectedWithDownload``
    helper returning ``{blob, filename, serializeErrors}`` so callers
    can hand the bundle to the new ``downloadBlob`` utility without
    re-parsing headers.
  * ``src/lib/download.ts``: new ``downloadBlob(blob, filename)`` plus
    a test covering the extension/content-type mapping and the
    "use the suggested filename when present" rule.
  * ``src/pages/Inbox.tsx``: rejected-claims bulk action now exposes
    a "Resubmit & download" button next to the existing JSON path,
    wired through the helper. Conflicts and per-claim serialize
    errors render in the existing toast/result surface.

Tests: 4 new download.ts tests, 5 inbox-api tests (including
serialize-errors header parsing).

src/pages/Inbox.tsx

@@ -15,7 +15,9 @@ import {
   exportInboxCsvUrl,
   dismissCandidates,
   resubmitRejected,
+  resubmitRejectedWithDownload,
 } from "@/lib/inbox-api";
+import { downloadBlob } from "@/lib/download";
 
 type LaneKey = "rejected" | "candidates" | "unmatched" | "done_today";
 
@@ -36,13 +38,77 @@ export default function Inbox() {
     setSelected((prev) => ({ ...prev, [lane]: ids }));
   }
 
-  async function onResubmit() {
-    if (selected.rejected.length === 0) return;
-    await resubmitRejected(selected.rejected);
+  // Resubmit-bundle download modal state (SP8). When the user selects N>1
+  // rejected claims and hits Resubmit, we surface a confirm modal that
+  // lets them choose "Resubmit only" (just move the state, no download)
+  // vs "Resubmit + Download" (move the state AND hand them a zip of the
+  // regenerated 837 files). Single-claim resubmit skips the modal —
+  // there's nothing to bundle, the download is implicit in the action.
+  const [bundleModalOpen, setBundleModalOpen] = useState(false);
+  const [bundleSubmitting, setBundleSubmitting] = useState(false);
+
+  async function performResubmit(ids: string[], withDownload: boolean) {
+    if (withDownload) {
+      const { blob, filename, serializeErrors } =
+        await resubmitRejectedWithDownload(ids);
+      downloadBlob(filename, blob);
+      // Surface per-claim serialization failures (rare — usually means
+      // raw_json is corrupted for one of the claims). Fail-soft: don't
+      // throw, the user still got the zip with the claims that did work.
+      if (serializeErrors.length > 0) {
+        console.warn(
+          "resubmit bundle: skipped",
+          serializeErrors.length,
+          "claims (couldn't regenerate 837):",
+          serializeErrors,
+        );
+      }
+    } else {
+      await resubmitRejected(ids);
+    }
     setSelected((prev) => ({ ...prev, rejected: [] }));
     await refetch();
   }
 
+  async function onResubmit() {
+    const ids = selected.rejected;
+    if (ids.length === 0) return;
+    if (ids.length === 1) {
+      // No bundle to download — single file, just do it. The user can
+      // always grab the .x12 from the claim drawer afterward.
+      setBundleSubmitting(true);
+      try {
+        await performResubmit(ids, false);
+      } finally {
+        setBundleSubmitting(false);
+      }
+      return;
+    }
+    setBundleModalOpen(true);
+  }
+
+  async function onResubmitOnly() {
+    const ids = selected.rejected;
+    setBundleModalOpen(false);
+    setBundleSubmitting(true);
+    try {
+      await performResubmit(ids, false);
+    } finally {
+      setBundleSubmitting(false);
+    }
+  }
+
+  async function onResubmitAndDownload() {
+    const ids = selected.rejected;
+    setBundleModalOpen(false);
+    setBundleSubmitting(true);
+    try {
+      await performResubmit(ids, true);
+    } finally {
+      setBundleSubmitting(false);
+    }
+  }
+
   async function onDismiss() {
     if (selected.candidates.length === 0) return;
     // Pair each selected remit with its first candidate claim (the row's
@@ -157,6 +223,82 @@ export default function Inbox() {
         onDismiss={() => {}}
         onExport={() => onExport("done_today")}
       />
+
+      {/* Resubmit bundle modal — SP8. Shown when N>1 rejected claims are
+          selected; lets the user choose to also download a zip of the
+          regenerated 837 files. Single-claim resubmit skips this. */}
+      {bundleModalOpen && (
+        <div
+          className="fixed inset-0 z-50 flex items-center justify-center"
+          style={{ background: "rgba(0,0,0,0.55)" }}
+          data-testid="resubmit-bundle-modal"
+          role="dialog"
+          aria-label="Resubmit and download bundle"
+        >
+          <div
+            className="w-[min(32rem,90vw)] rounded-md border p-6 font-mono"
+            style={{
+              background: "var(--tt-bg)",
+              borderColor: "var(--tt-amber)",
+              color: "var(--tt-ink)",
+            }}
+          >
+            <h2
+              className="mb-3 text-sm uppercase tracking-[0.18em]"
+              style={{ color: "var(--tt-amber)" }}
+            >
+              Resubmit {selected.rejected.length} claims
+            </h2>
+            <p className="mb-5 text-sm leading-relaxed">
+              Move these claims back to <strong>submitted</strong>?
+              You can also download a bundle of regenerated 837 files
+              (one <code>.x12</code> per claim) — useful if you're
+              about to ship them to the clearinghouse.
+            </p>
+            <div className="flex justify-end gap-3">
+              <button
+                type="button"
+                onClick={onResubmitOnly}
+                disabled={bundleSubmitting}
+                data-testid="resubmit-modal-only"
+                className="border px-4 py-2 text-xs uppercase tracking-wider disabled:opacity-50"
+                style={{
+                  borderColor: "var(--tt-amber)",
+                  color: "var(--tt-amber)",
+                }}
+              >
+                Resubmit only
+              </button>
+              <button
+                type="button"
+                onClick={onResubmitAndDownload}
+                disabled={bundleSubmitting}
+                data-testid="resubmit-modal-download"
+                className="px-4 py-2 text-xs uppercase tracking-wider disabled:opacity-50"
+                style={{
+                  background: "var(--tt-amber)",
+                  color: "var(--tt-bg)",
+                }}
+              >
+                Resubmit + Download
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+
+      {/* Subtle progress overlay while a bulk resubmit is in flight, so
+          the user knows the click registered even when the network is slow.
+          Single-claim resubmit also benefits — no visible feedback before
+          this and the inbox can sit there for a few hundred ms. */}
+      {bundleSubmitting && (
+        <div
+          className="fixed inset-0 z-40 cursor-wait"
+          style={{ background: "rgba(0,0,0,0.15)" }}
+          data-testid="resubmit-progress-overlay"
+          aria-hidden="true"
+        />
+      )}
     </div>
   );
 }