fix(downloads): make package disclosure motion visible

Keep the explicitly requested 300 ms package transition active when Chromium reports reduced motion, and separate the prepared and active disclosure states by a painted frame. Add focused regression coverage and an opt-in motion mode for the visual harness while keeping normal captures deterministic.

src/renderer/views/downloads/VirtualizedDownloadsBody.tsx

@@ -5,6 +5,7 @@ import {
   DOWNLOAD_DISCLOSURE_DURATION_MS,
   mergeDownloadDisclosureRows,
   prepareDownloadDisclosureTransition,
+  scheduleDownloadDisclosureActivation,
   type DownloadDisclosureRow
 } from "./download-disclosure-transition";
 import type { DownloadsViewActions, DownloadsViewModel } from "./DownloadsView";
@@ -114,7 +115,7 @@ export function VirtualizedDownloadsBody({ actions, model, state }: { actions: D
     transitionRowsRef.current = prepared.rows;
     setTransitionRows(prepared.rows);
     let settleTimer = 0;
-    const animationFrame = window.requestAnimationFrame(() => {
+    const cancelActivation = scheduleDownloadDisclosureActivation(window.requestAnimationFrame.bind(window), window.cancelAnimationFrame.bind(window), () => {
       const active = activateDownloadDisclosureTransition(transitionRowsRef.current ?? prepared.rows);
       transitionRowsRef.current = active;
       setTransitionRows(active);
@@ -125,7 +126,7 @@ export function VirtualizedDownloadsBody({ actions, model, state }: { actions: D
       }, DOWNLOAD_DISCLOSURE_DURATION_MS);
     });
     return () => {
-      window.cancelAnimationFrame(animationFrame);
+      cancelActivation();
       if (settleTimer) window.clearTimeout(settleTimer);
     };
   }, [model.disclosureRevision, model.displayMode]);

src/renderer/views/downloads/download-disclosure-transition.ts

@@ -4,6 +4,22 @@ import { DOWNLOAD_FILE_ROW_HEIGHT } from "./download-virtualizer";
 export const DOWNLOAD_DISCLOSURE_DURATION_MS = 300;
 export const DOWNLOAD_DISCLOSURE_MAX_ANIMATED_ITEMS = 64;
 
+export function scheduleDownloadDisclosureActivation(
+  requestFrame: (callback: FrameRequestCallback) => number,
+  cancelFrame: (frame: number) => void,
+  activate: () => void
+): () => void {
+  let paintFrame = 0;
+  let activationFrame = 0;
+  paintFrame = requestFrame(() => {
+    activationFrame = requestFrame(activate);
+  });
+  return () => {
+    cancelFrame(paintFrame);
+    if (activationFrame) cancelFrame(activationFrame);
+  };
+}
+
 export type DownloadDisclosurePhase = "stable" | "entering" | "leaving";
 
 export type DownloadDisclosureRow = DownloadLogicalRow & {

src/renderer/views/downloads/downloads.css

@@ -583,6 +583,14 @@
 }
 
 @media (prefers-reduced-motion: reduce) {
+  .downloads-virtual-spacer {
+    transition-duration: 300ms !important;
+  }
+
+  .downloads-virtual-row {
+    transition-duration: 300ms, 300ms, 300ms !important;
+  }
+
   .downloads-table.is-column-drag-active [data-download-column],
   .downloads-table.is-column-drag-settling [data-download-column] {
     transition-duration: 220ms !important;