diff --git a/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts b/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
index e2ae7411..54b333ed 100644
--- a/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
+++ b/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
@@ -269,6 +269,20 @@ export function boardMediaItemsToMediaFiles(items: WorkOrderBoardMediaItem[]): M
   }));
 }
 
+/**
+ * `GET workorders/{id}/detail` info serializes the board row's `MediaCount` as 0 — the detail
+ * DTO inherits the field but the service never sets it — so trusting it verbatim would leave the
+ * slide-over closability gate reporting "At least 1 photo" even after an upload. Take the larger
+ * of the reported count and the stored (non-legacy) attachments: a positive API count still wins,
+ * but a spurious (or omitted) 0 can no longer mask media that are actually present.
+ */
+function resolveDetailMediaCount(infoRaw: unknown, media: WorkOrderBoardMediaItem[]): number {
+  const record = asRecord(infoRaw);
+  const explicit = record.mediaCount ?? record.MediaCount;
+  const nonLegacyCount = media.filter((item) => !item.isLegacy).length;
+  return Math.max(typeof explicit === "number" ? explicit : 0, nonLegacyCount);
+}
+
 export function mapWorkOrderBoardDetail(raw: unknown): WorkOrderBoardDetail {
   const root = asRecord(raw);
   const infoRaw = root.info ?? root.Info ?? root;
@@ -283,8 +297,10 @@ export function mapWorkOrderBoardDetail(raw: unknown): WorkOrderBoardDetail {
     : [];
   const media = Array.isArray(mediaRaw) ? mediaRaw.map(mapBoardDetailMediaItem) : [];
 
+  const info = mapWorkOrderTableRow(infoRaw);
+
   return {
-    info: mapWorkOrderTableRow(infoRaw),
+    info: { ...info, mediaCount: resolveDetailMediaCount(infoRaw, media) },
     completion: mapCompletion(completionRaw ?? {}),
     comments,
     audit,
diff --git a/src/test/domain/work-orders/mappers/work-order-board-detail-mapper.test.ts b/src/test/domain/work-orders/mappers/work-order-board-detail-mapper.test.ts
index 7f34bcc8..fb24f6b5 100644
--- a/src/test/domain/work-orders/mappers/work-order-board-detail-mapper.test.ts
+++ b/src/test/domain/work-orders/mappers/work-order-board-detail-mapper.test.ts
@@ -6,6 +6,10 @@ import {
   mapBoardDetailMediaItem,
   mapWorkOrderBoardDetail,
 } from "@/domain/work-orders/mappers/work-order-board-detail-mapper";
+import {
+  getClosabilityGaps,
+  tableRowToClosabilityInput,
+} from "@/domain/work-orders/utils/wo-closability";
 
 const SAMPLE_DETAIL = {
   info: {
@@ -279,3 +283,56 @@ describe("mapWorkOrderBoardDetail", () => {
     expect(completionForm.get("file")).toBeInstanceOf(File);
   });
 });
+
+describe("mapWorkOrderBoardDetail media count (SH-339)", () => {
+  const reactiveInfo = { ...SAMPLE_DETAIL.info, workOrderType: 6 };
+
+  it("derives mediaCount from stored media when detail info omits it", () => {
+    const detail = mapWorkOrderBoardDetail({ ...SAMPLE_DETAIL, info: reactiveInfo });
+
+    expect(detail.info.type).toBe("Reactive");
+    expect(detail.info.mediaCount).toBe(2);
+    expect(getClosabilityGaps(tableRowToClosabilityInput(detail.info))).not.toContain(
+      "At least 1 photo",
+    );
+  });
+
+  it("prefers stored media when detail info reports an explicit zero", () => {
+    const detail = mapWorkOrderBoardDetail({
+      ...SAMPLE_DETAIL,
+      info: { ...reactiveInfo, mediaCount: 0 },
+    });
+
+    expect(detail.info.mediaCount).toBe(2);
+    expect(getClosabilityGaps(tableRowToClosabilityInput(detail.info))).not.toContain(
+      "At least 1 photo",
+    );
+  });
+
+  it("does not count legacy URL-column media, matching the board row count", () => {
+    const detail = mapWorkOrderBoardDetail({
+      ...SAMPLE_DETAIL,
+      info: reactiveInfo,
+      media: [
+        {
+          id: -1,
+          category: 1,
+          url: "https://cdn.example.com/legacy.jpg",
+          fileName: "legacy.jpg",
+          isLegacy: true,
+        },
+      ],
+    });
+
+    expect(detail.info.mediaCount).toBe(0);
+  });
+
+  it("keeps an explicit info mediaCount", () => {
+    const detail = mapWorkOrderBoardDetail({
+      ...SAMPLE_DETAIL,
+      info: { ...reactiveInfo, mediaCount: 5 },
+    });
+
+    expect(detail.info.mediaCount).toBe(5);
+  });
+});