feat(downloads): animate priority reordering

Rename the package disclosure option to a general animations switch and use it for both disclosure and priority-order motion. Keep previously visible virtual rows mounted during reorders, animate measured start and target positions for 1.5 seconds, and cancel all motion immediately when the setting is disabled. Extend the isolated renderer fixture so enabled and disabled behavior can be measured without touching user download state.

tests/visual/mock-electron-api.ts

@@ -12,11 +12,19 @@ export function createVisualElectronApi(
   fixture: VisualFixture,
   search = typeof window === "undefined" ? "" : window.location.search
 ): ElectronApi {
-  const historyState = new URLSearchParams(search).get("history-state");
+  const searchParams = new URLSearchParams(search);
+  const historyState = searchParams.get("history-state");
+  if (searchParams.get("animations") === "off") fixture.snapshot.settings.animatePackageDisclosure = false;
   let historyRequestCount = 0;
+  const stateUpdateListeners = new Set<Parameters<ElectronApi["onStateUpdate"]>[0]>();
+  const emitStateUpdate = (): void => {
+    const snapshot = clone(fixture.snapshot);
+    for (const listener of stateUpdateListeners) listener(snapshot);
+  };
   const updateSettings = (settings: RendererSettingsUpdate): RendererSettings => {
     const { archivePasswordList: _archivePasswordList, notifyUrl: _notifyUrl, ...safe } = settings;
     Object.assign(fixture.snapshot.settings, safe);
+    emitStateUpdate();
     return clone(fixture.snapshot.settings);
   };
 
@@ -376,9 +384,24 @@ export function createVisualElectronApi(
       : { ok: false, reason: "entry-not-found" },
     setPackagePriority: async (packageId, priority) => {
       const entry = fixture.snapshot.session.packages[packageId];
-      if (entry) {
-        entry.priority = priority;
+      if (!entry || entry.priority === priority) return;
+      entry.priority = priority;
+      const order = fixture.snapshot.session.packageOrder;
+      const currentIndex = order.indexOf(packageId);
+      if (currentIndex >= 0) {
+        order.splice(currentIndex, 1);
+        const priorityRank = { high: 0, normal: 1, low: 2 } as const;
+        let insertAt = order.length;
+        for (let index = 0; index < order.length; index += 1) {
+          const otherPriority = fixture.snapshot.session.packages[order[index]]?.priority || "normal";
+          if (priorityRank[otherPriority] > priorityRank[priority]) {
+            insertAt = index;
+            break;
+          }
+        }
+        order.splice(insertAt, 0, packageId);
       }
+      emitStateUpdate();
     },
     skipItems: async (itemIds) => {
       for (const itemId of itemIds) {
@@ -413,7 +436,10 @@ export function createVisualElectronApi(
       fixture.snapshot.session.running = true;
     },
     reportRendererError: () => {},
-    onStateUpdate: () => stableNoopUnsubscribe,
+    onStateUpdate: (callback) => {
+      stateUpdateListeners.add(callback);
+      return () => stateUpdateListeners.delete(callback);
+    },
     onClipboardDetected: () => stableNoopUnsubscribe,
     onUpdateInstallProgress: () => stableNoopUnsubscribe
   };