Test the live-photo writer's fsyncs (closes #130)

A test checks that the live-photo writer fsyncs the image's and the
video's temp files before renaming either into place, and fsyncs the
directory after both renames, as the writeAtomic test does for one file.

Model: opus-5-5

TODO.md

@@ -21,6 +21,11 @@ declares one.
 
 # Completed Steps
 
+- 2026-09-28: Tested the live-photo writer's fsyncs (issue 130). A test checks
+  that the image's and the video's temp files are fsynced before either is
+  renamed into place, and the directory after both renames, as the `writeAtomic`
+  test does for one file.
+
 - 2026-09-23: Live photos are stored as their image and their video (issue 107).
   A live photo, which Ente stores as one ZIP, is unpacked as it downloads into
   `<fileID>.<ext>` for the image and for the video, each with its extension from

test/download/download.test.ts

@@ -1909,6 +1909,24 @@ describe("downloadFile live photos", () => {
         ]);
     });
 
+    it("fsyncs each part's temp file before the renames and the directory after", async () => {
+        const t = setup(livePhotoZip(), livePhoto);
+
+        await t.run();
+
+        // The same durability contract as `writeAtomic`, for two files: both
+        // temp files are on disk before either is renamed into place, and the
+        // directory is fsynced once both renames are done.
+        const [imageTmp, videoTmp] = renameHook.calls.map((c) => c.from);
+        expect(durabilityHook.events).toEqual([
+            `sync:w:${imageTmp}`,
+            `sync:w:${videoTmp}`,
+            `rename:${join(t.dir, "f.heic")}`,
+            `rename:${join(t.dir, "f.mov")}`,
+            `sync:r:${t.dir}`,
+        ]);
+    });
+
     it("stores neither part when the video cannot be renamed into place", async () => {
         const t = setup(livePhotoZip(), livePhoto);
         renameHook.failWith = new Error("simulated rename failure");