fix(sftp): persist repaired background transfer hierarchy

application/state/sftpTransferCenterStore.test.ts

@@ -4007,3 +4007,111 @@ test("partial cancel failure resets recovered folder children so the re-walk can
     assert.equal(afterFullCancel.find((row) => row.id === id)?.status, "cancelled");
   }
 });
+
+test("lifecycle hierarchy snapshot stays stable on bytes and changes on actual state transitions", () => {
+  const store = createSftpTransferCenterStore();
+  store.publishOwner("panel", [makeTask("hierarchy-live")]);
+  const hierarchy = store.getLifecycleSnapshot();
+  store.patchTask("hierarchy-live", { transferredBytes: 5, speed: 3 });
+  assert.equal(store.getLifecycleSnapshot(), hierarchy);
+  assert.equal(store.getTask("hierarchy-live")?.transferredBytes, 5);
+  store.getSnapshot(); // Other progress consumers must not invalidate the hierarchy.
+  assert.equal(store.getLifecycleSnapshot(), hierarchy);
+  store.patchTask("hierarchy-live", { status: "failed", error: "fixture failure" });
+  assert.notEqual(store.getLifecycleSnapshot(), hierarchy);
+  assert.equal(store.getLifecycleSnapshot().tasks[0].status, "failed");
+});
+
+test("progress that admits or changes a task lifecycle also refreshes the hierarchy", () => {
+  const store = createSftpTransferCenterStore();
+  const initial = store.getLifecycleSnapshot();
+  store.ingestBackgroundEvent({ type: "progress", transferId: "late-start", transferred: 1 });
+  const admitted = store.getLifecycleSnapshot();
+  assert.notEqual(admitted, initial);
+  assert.equal(admitted.tasks[0].id, "late-start");
+  store.publishOwner("panel", [makeTask("queued-progress", "queued")]);
+  const queued = store.getLifecycleSnapshot();
+  store.ingestBackgroundEvent({ type: "progress", transferId: "queued-progress", transferred: 3 });
+  assert.notEqual(store.getLifecycleSnapshot(), queued);
+  assert.equal(store.getLifecycleSnapshot().tasks.find((task) => task.id === "queued-progress")?.status, "transferring");
+  const live = store.getLifecycleSnapshot();
+  store.ingestBackgroundEvent({ type: "progress", transferId: "queued-progress", transferred: 4 });
+  assert.equal(store.getLifecycleSnapshot(), live);
+});
+
+test("admission updates hierarchy state without forcing full owner lifecycle work", () => {
+  const store = createSftpTransferCenterStore();
+  const task = makeTask("admitted-hierarchy", "queued");
+  store.publishOwner("panel", [task]);
+  const queued = store.getLifecycleSnapshot();
+  let lifecycleNotifications = 0;
+  store.subscribe(() => { lifecycleNotifications += 1; });
+  assert.equal(store.admitTaskRun(task), "ready");
+  assert.notEqual(store.getLifecycleSnapshot(), queued);
+  assert.equal(store.getLifecycleSnapshot().tasks[0].status, "transferring");
+  assert.equal(lifecycleNotifications, 0, "dispatch admission keeps its existing lightweight fanout");
+});
+
+
+test("same-byte and ignored terminal events publish repaired background hierarchy immediately", () => {
+  for (const { status, type } of [
+    { status: "transferring", type: "progress" },
+    { status: "completed", type: "progress" },
+    { status: "completed", type: "completed" },
+    { status: "failed", type: "failed" },
+  ] as const) {
+    const store = createSftpTransferCenterStore();
+    store.publishOwner("panel", [{ ...makeTask("folder"), isDirectory: true }]);
+    store.publishOwner("background-agent", [{ ...makeTask("orphan", status), background: true }]);
+    const beforeRepair = store.getLifecycleSnapshot();
+    let lifecycleNotifications = 0;
+    store.subscribe(() => { lifecycleNotifications += 1; });
+    store.ingestBackgroundEvent({ type, transferId: "orphan", parentTaskId: "folder", transferred: 2 });
+    const repaired = store.getLifecycleSnapshot();
+    assert.notEqual(repaired, beforeRepair, status);
+    assert.equal(repaired.tasks.find((task) => task.id === "orphan")?.parentTaskId, "folder", status);
+    assert.equal(repaired.tasks.find((task) => task.id === "orphan")?.background, false, status);
+    assert.equal(lifecycleNotifications, 0, "hierarchy repair keeps lightweight owner fanout");
+    store.ingestBackgroundEvent({ type: "progress", transferId: "orphan", parentTaskId: "folder", transferred: 3 });
+    assert.equal(store.getLifecycleSnapshot(), repaired, "subsequent byte ticks preserve the repaired hierarchy without rebuilding it");
+    assert.equal(store.getTask("orphan")?.parentTaskId, "folder");
+  }
+});
+
+test("repaired terminal hierarchy survives restart without another lifecycle event", (t) => {
+  t.mock.timers.enable({ apis: ["setTimeout", "Date"], now: Date.now() });
+  for (const status of ["completed", "failed", "cancelled"] as const) {
+    let persisted = "";
+    let writes = 0;
+    const store = createSftpTransferCenterStore({ read: () => null, write: (value) => { persisted = value; writes += 1; } });
+    store.publishOwner("panel", [{ ...makeTask("folder"), isDirectory: true }]);
+    store.publishOwner("background-agent", [{ ...makeTask("orphan", status), background: true }]);
+    t.mock.timers.tick(300);
+    assert.equal(JSON.parse(persisted).tasks.find((task: TransferTask) => task.id === "orphan")?.parentTaskId, undefined);
+    let lifecycleNotifications = 0;
+    store.subscribe(() => { lifecycleNotifications += 1; });
+    const beforeRepairWrites = writes;
+    store.ingestBackgroundEvent({ type: "progress", transferId: "orphan", parentTaskId: "folder", transferred: 2 });
+    t.mock.timers.tick(300);
+    assert.equal(writes, beforeRepairWrites + 1, "structural repair is saved even when the terminal event is ignored");
+    const savedChild = JSON.parse(persisted).tasks.find((task: TransferTask) => task.id === "orphan");
+    assert.equal(savedChild?.parentTaskId, "folder", status);
+    assert.equal(savedChild?.background, false, status);
+    assert.equal(savedChild?.ownerId, "panel", status);
+    const restored = createSftpTransferCenterStore({ read: () => persisted, write: () => {} });
+    const child = restored.getTask("orphan");
+    if (status === "completed") {
+      assert.equal(child, undefined, "existing restore compaction retains completed children in their folder checkpoint");
+      assert.equal(restored.getTask("folder")?.directoryResumeCheckpoint?.completedEntries, 1);
+    } else {
+      assert.equal(child?.parentTaskId, "folder", status);
+      assert.equal(child?.background, false, status);
+      assert.equal(child?.ownerId, "panel", status);
+    }
+    assert.equal(lifecycleNotifications, 0, "repair retains lightweight owner notifications");
+    const settledWrites = writes;
+    store.ingestBackgroundEvent({ type: "progress", transferId: "orphan", parentTaskId: "folder", transferred: 3 });
+    t.mock.timers.tick(300);
+    assert.equal(writes, settledWrites, "unchanged late progress does not schedule recurring writes");
+  }
+});

application/state/sftpTransferCenterStore.ts

@@ -109,6 +109,8 @@ export interface SftpTransferCenterStore {
    */
   subscribeProgress(listener: Listener): () => void;
   getSnapshot(): SftpTransferCenterSnapshot;
+  /** Stable task hierarchy between lifecycle changes; live rows read getTask. */
+  getLifecycleSnapshot(): SftpTransferCenterSnapshot;
   /** Stable identity when badge counts are unchanged (avoids TopTabs thrash). */
   getBadgeSnapshot(): { count: number; hasAttention: boolean };
   /** Single task row — same object identity until that row is patched. */
@@ -213,6 +215,21 @@ function buildBadgeSnapshot(tasks: readonly TransferTask[]): { count: number; ha
   };
 }
 
+/** Fields used by grouping, ordering and batch-action eligibility. */
+function hasTransferListMetadataChange(before: TransferTask | undefined, after: TransferTask | undefined): boolean {
+  if (!before || !after) return before !== after;
+  return before.status !== after.status
+    || before.parentTaskId !== after.parentTaskId
+    || before.background !== after.background
+    || before.startTime !== after.startTime
+    || before.priority !== after.priority
+    || before.ownerId !== after.ownerId
+    || before.resumable !== after.resumable
+    || before.reconnectRequired !== after.reconnectRequired
+    || Boolean(before.conflict) !== Boolean(after.conflict)
+    || (before.status === "failed" && ((before.checkpointBytes ?? 0) > 0) !== ((after.checkpointBytes ?? 0) > 0));
+}
+
 const TERMINAL_OWNER_STATUSES = new Set<TransferTask["status"]>([
   "completed",
   "cancelled",
@@ -420,6 +437,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
     event: BackgroundTransferEvent;
   }>>();
   let snapshot = tasks.length > 0 ? buildSnapshot(tasks) : EMPTY_SNAPSHOT;
+  let lifecycleSnapshot = snapshot;
   let badgeSnapshot = buildBadgeSnapshot(tasks);
   let snapshotDirty = false;
   const listeners = new Set<Listener>();
@@ -695,6 +713,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
     }
     snapshotDirty = false;
     snapshot = buildSnapshot(tasks);
+    lifecycleSnapshot = snapshot;
     refreshBadgeSnapshot();
     persist(shouldPersistImmediately);
     notifyDedicatedResumeWaiters();
@@ -707,19 +726,24 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
   };
 
   /** Progress-only: mutate tasks, defer snapshot rebuild, wake progress UI only. */
-  const emitProgress = (persistImmediately = false) => {
+  const emitProgress = (persistImmediately = false, lifecycleChanged = false) => {
     if (deferRestoreReplayEmits) {
       snapshotDirty = true;
       persistenceDirty = persistenceDirty || persistImmediately;
       return;
     }
     snapshotDirty = true;
+    // Admission/late progress may change a row's lifecycle without the costly
+    // prune/persist path. Keep the list hierarchy current, coalescing its UI
+    // notification with progress instead of waking owner lifecycle listeners.
+    if (lifecycleChanged) lifecycleSnapshot = buildSnapshot(tasks);
     // Never JSON.stringify/localStorage on the pure-progress path. Sync storage
     // on large directory histories freezes CSS spinners every few seconds.
     // Pause / complete / fingerprint / lifecycle still force persist below.
     if (persistImmediately) {
       snapshotDirty = false;
       snapshot = buildSnapshot(tasks);
+      lifecycleSnapshot = snapshot;
       refreshBadgeSnapshot();
       persist(true);
       notifyDedicatedResumeWaiters();
@@ -1401,6 +1425,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
       return () => progressListeners.delete(listener);
     },
     getSnapshot: () => ensureSnapshot(),
+    getLifecycleSnapshot: () => lifecycleSnapshot,
     getBadgeSnapshot: () => badgeSnapshot,
     admitTaskRun(incoming, pausedAtResume, completedAtRestart) {
       const rootId = incoming.parentTaskId ?? incoming.id;
@@ -1454,7 +1479,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
       };
       tasks = next;
       captureObservedTask(next[index]);
-      emitProgress(false);
+      emitProgress(false, hasTransferListMetadataChange(existing, next[index]));
       return "ready";
     },
     observeTaskSettlement(expected, ignoredCompletion, onIdentityConflict) {
@@ -1773,7 +1798,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
         if (fingerprintChanged) emit(true);
         else if (directoryCheckpointChanged) emit(true);
         else if (lifecycleChanged) emit();
-        else emitProgress(false);
+        else emitProgress(false, hasTransferListMetadataChange(task, nextTask));
       }
     },
     upsertTasks(incoming) {
@@ -2173,6 +2198,8 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
       }
       let existingIndex = tasks.findIndex((task) => task.id === event.transferId);
       let existing = tasks[existingIndex];
+      const beforeEvent = existing;
+      let parentControlsChanged = false;
       const eventParent = event.parentTaskId
         ? tasks.find((task) => task.id === event.parentTaskId)
         : undefined;
@@ -2190,7 +2217,16 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
         } : task);
         existing = tasks[existingIndex];
         captureObservedTask(existing);
+        // Structural recovery must survive restart even if an unchanged or
+        // already-terminal event returns before the normal persistence path.
+        persist();
       }
+      // Hierarchy repair has already changed the live row. Even an otherwise
+      // ignored event must publish that change; ordinary progress still emits
+      // only once at the end, without a second directory-sized snapshot build.
+      const publishRepairedHierarchy = () => {
+        if (existing !== beforeEvent) emitProgress(false, true);
+      };
       // A delayed child progress event can arrive after the renderer compacted
       // that completed child into its parent checkpoint. Never resurrect it as
       // a live row, especially after the parent itself has finished.
@@ -2216,9 +2252,11 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
         // Allow a late explicit cancel to stick; ignore everything else.
         if (event.type === "completed" || event.type === "failed") {
           // Keep existing terminal state (prefer cancelled over late completed).
+          publishRepairedHierarchy();
           return;
         }
         if (event.type === "queued" || event.type === "started" || event.type === "progress" || event.type === "pausing" || event.type === "resumed" || event.type === "paused") {
+          publishRepairedHierarchy();
           return;
         }
       }
@@ -2263,6 +2301,7 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
           && sameOptional(event.resumable, existing.resumable)
           && sameOptional(event.pauseUnavailableReason, existing.pauseUnavailableReason)
         ) {
+          publishRepairedHierarchy();
           return;
         }
       }
@@ -2452,6 +2491,8 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
           };
         });
         if (event.resumable === false && existing.parentTaskId) {
+          const parent = tasks.find((task) => task.id === existing.parentTaskId);
+          parentControlsChanged = parent !== undefined && parent.resumable !== false;
           tasks = tasks.map((task) => task.id === existing.parentTaskId ? {
             ...task,
             resumable: false,
@@ -2508,8 +2549,11 @@ export function createSftpTransferCenterStore(persistence?: StorePersistence): S
       if (existingIndex >= 0) captureObservedTask(tasks[existingIndex]);
       // Progress-only ticks skip prune + coalesce listener paints; lifecycle
       // events still take the full emit path so UI never lags on pause/cancel.
+      const currentTask = tasks[existingIndex];
+      const hierarchyOrLifecycleChanged = parentControlsChanged
+        || hasTransferListMetadataChange(beforeEvent, currentTask);
       if (event.type === "progress" && !persistImmediately) {
-        emitProgress(false);
+        emitProgress(false, hierarchyOrLifecycleChanged);
       } else {
         emit(persistImmediately);
       }

components/GlobalSftpTransferCenter.children-performance.test.tsx

@@ -0,0 +1,156 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import React from "react";
+import { createDomRenderer, dispatchDomEvent, flushEffects, installDomEnvironment, runWithAct } from "./test-support/renderReactDom.tsx";
+
+test("expanded folder history bounds mounted files, isolates progress, and reaches the final child", async (t) => {
+  const env = installDomEnvironment();
+  const previous = new Map<string, PropertyDescriptor | undefined>();
+  for (const [key, value] of Object.entries({
+    MutationObserver: env.window.MutationObserver,
+    NodeFilter: env.window.NodeFilter,
+    HTMLInputElement: env.window.HTMLInputElement,
+    Element: env.window.Element,
+    requestAnimationFrame: (callback: FrameRequestCallback) => setTimeout(() => callback(Date.now()), 0),
+    cancelAnimationFrame: clearTimeout,
+  })) {
+    previous.set(key, Object.getOwnPropertyDescriptor(globalThis, key));
+    Object.defineProperty(globalThis, key, { configurable: true, writable: true, value });
+  }
+  Object.defineProperties(env.window.HTMLElement.prototype, {
+    offsetWidth: { configurable: true, get: () => 460 },
+    offsetHeight: { configurable: true, get() { return this.dataset.section === "global-sftp-transfer-child-list" ? 192 : 460; } },
+  });
+  const { I18nProvider } = await import("../application/i18n/I18nProvider.tsx");
+  const { sftpTransferCenterStore: store } = await import("../application/state/sftpTransferCenterStore.ts");
+  const { GlobalSftpTransferCenter } = await import("./GlobalSftpTransferCenter.tsx");
+  const { TooltipProvider } = await import("./ui/tooltip.tsx");
+  const renderer = await createDomRenderer(env.document);
+  t.after(async () => {
+    await renderer.unmount();
+    for (const [key, descriptor] of previous) {
+      if (descriptor) Object.defineProperty(globalThis, key, descriptor);
+      else Reflect.deleteProperty(globalThis, key);
+    }
+    env.cleanup();
+  });
+  const childCount = 1_000;
+  const base = {
+    fileName: "folder", sourcePath: "/source", targetPath: "/target",
+    sourceConnectionId: "source", targetConnectionId: "local", direction: "download" as const,
+    totalBytes: 1_000, transferredBytes: 0, speed: 0, startTime: 1,
+  };
+  store.publishOwner("children-performance", [
+    { ...base, id: "folder", status: "transferring", isDirectory: true, progressMode: "files" },
+    ...Array.from({ length: childCount }, (_, index) => ({
+      ...base, id: `child-${index}`, fileName: `child-${index}.bin`, sourcePath: `/source/${index}`, targetPath: `/target/${index}`,
+      status: index === 0 ? "transferring" as const : "queued" as const,
+      startTime: index + 2, isDirectory: false, parentTaskId: "folder",
+    })),
+  ]);
+  await renderer.render(<I18nProvider locale="en"><TooltipProvider><GlobalSftpTransferCenter /></TooltipProvider></I18nProvider>);
+  const click = async (selector: string) => {
+    const element = env.document.querySelector(selector);
+    assert.ok(element, selector);
+    await dispatchDomEvent(element, new env.window.MouseEvent("click", { bubbles: true }));
+    await flushEffects();
+  };
+  await click("[data-section=global-sftp-transfer-toggle]");
+  await click('button[aria-label="Show files"]');
+  const childList = () => env.document.querySelector<HTMLElement>("[data-section=global-sftp-transfer-child-list]");
+  const childRows = () => childList()?.querySelectorAll('[data-transfer-status]') ?? [];
+  assert.ok(childRows().length > 0 && childRows().length < 40, `mounted ${childRows().length} child rows`);
+  assert.match(childList()?.textContent ?? "", /child-0.bin/);
+
+  let orderReads = 0;
+  for (const task of store.getSnapshot().tasks) {
+    if (!task.parentTaskId) continue;
+    const startTime = task.startTime;
+    Object.defineProperty(task, "startTime", { configurable: true, enumerable: true, get: () => { orderReads += 1; return startTime; } });
+  }
+  await runWithAct(async () => {
+    store.patchTask("child-0", { transferredBytes: 500, speed: 100 });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.ok(orderReads < 20, `one byte update re-sorted the directory (${orderReads} reads)`);
+  assert.match(childList()?.textContent ?? "", /500 B/);
+
+  const pauseAll = () => [...env.document.querySelectorAll<HTMLButtonElement>('button')].find((button) => button.textContent?.trim() === "Pause all")!;
+  assert.equal(pauseAll().disabled, false);
+  await runWithAct(async () => {
+    store.ingestBackgroundEvent({ type: "progress", transferId: "child-0", transferred: 600, resumable: false, pauseUnavailableReason: "fixture cannot pause" });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(store.getTask("folder")?.resumable, false, "a child's backend capability also limits its folder");
+  assert.equal(pauseAll().disabled, true, "batch controls must use the current backend capability");
+  await runWithAct(async () => {
+    store.patchTask("folder", { resumable: true });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(pauseAll().disabled, false, "metadata-only patches must refresh eligibility too");
+  await runWithAct(async () => {
+    store.ingestBackgroundEvent({ type: "progress", transferId: "child-0", transferred: 650, resumable: false });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(pauseAll().disabled, true, "a parent-only capability change is reflected even when the child already reported false");
+  await runWithAct(async () => {
+    store.patchTask("folder", { resumable: false });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(pauseAll().disabled, true);
+  orderReads = 0;
+  await runWithAct(async () => {
+    store.ingestBackgroundEvent({ type: "progress", transferId: "child-0", transferred: 700, resumable: false });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.ok(orderReads < 20, "repeated capability metadata on byte ticks does not re-sort the directory");
+  await runWithAct(() => store.publishOwner("failed-control", [{
+    ...base, id: "failed-control", status: "failed", isDirectory: false, endTime: Date.now(), resumable: true, checkpointBytes: 0,
+  }]));
+  const resumeAll = () => [...env.document.querySelectorAll<HTMLButtonElement>('button')].find((button) => button.textContent?.trim() === "Resume all")!;
+  assert.equal(resumeAll().disabled, true);
+  await runWithAct(async () => {
+    store.patchTask("failed-control", { checkpointBytes: 20 });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(resumeAll().disabled, false, "a newly available failed-task checkpoint enables the existing resume action");
+
+  const list = childList()!;
+  list.scrollTop = 24 * childCount - 192;
+  await dispatchDomEvent(list, new env.window.Event("scroll"));
+  await flushEffects();
+  assert.ok(childRows().length > 0 && childRows().length < 40);
+  assert.match(childList()?.textContent ?? "", /child-999.bin/);
+  await runWithAct(() => store.patchTask("child-999", { status: "completed", transferredBytes: 1_000 }));
+  assert.equal(store.getTask("folder")?.directoryResumeCheckpoint?.completedEntries, 1, "completed files remain counted in the existing compact folder checkpoint");
+  assert.equal(store.getTask("child-999"), undefined, "the existing completion compaction still owns history retention");
+  assert.equal(store.getTask("child-500")?.status, "queued");
+  await click('button[aria-label="Hide files"]');
+  assert.equal(childList(), null);
+  await click('button[aria-label="Show files"]');
+  assert.ok(childRows().length > 0 && childRows().length < 40);
+  assert.equal(store.getSnapshot().tasks.filter((task) => task.parentTaskId === "folder").length, childCount - 1, "virtualization never drops queued files");
+  await runWithAct(() => {
+    store.publishOwner("repair-folder", [{ ...base, id: "repair-folder", fileName: "repaired folder", status: "transferring", isDirectory: true }]);
+    store.publishOwner("repair-background", [{ ...base, id: "repair-child", fileName: "repaired-child.bin", status: "transferring", isDirectory: false, background: true, transferredBytes: 10 }]);
+  });
+  const repairedFolderRow = () => [...env.document.querySelectorAll<HTMLElement>('[data-section=global-sftp-transfer-row]')].find((row) => row.textContent?.includes("repaired folder"))!;
+  assert.equal(repairedFolderRow().querySelector('button[aria-label="Show files"]'), null);
+  await runWithAct(async () => {
+    store.ingestBackgroundEvent({ type: "progress", transferId: "repair-child", parentTaskId: "repair-folder", transferred: 10 });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  const repairedExpand = repairedFolderRow().querySelector('button[aria-label="Show files"]');
+  assert.ok(repairedExpand, "same-byte hierarchy repair immediately exposes the folder's child");
+  await dispatchDomEvent(repairedExpand, new env.window.MouseEvent("click", { bubbles: true }));
+  await flushEffects();
+  assert.match(repairedFolderRow().textContent ?? "", /repaired-child.bin/);
+  const repairedHierarchy = store.getLifecycleSnapshot();
+  await runWithAct(async () => {
+    store.ingestBackgroundEvent({ type: "progress", transferId: "repair-child", parentTaskId: "repair-folder", transferred: 11 });
+    await new Promise((resolve) => setTimeout(resolve, 20));
+  });
+  assert.equal(store.getLifecycleSnapshot(), repairedHierarchy);
+  assert.match(repairedFolderRow().textContent ?? "", /repaired-child.bin/);
+  await click("[data-section=global-sftp-transfer-toggle]");
+});

components/GlobalSftpTransferCenter.tsx

@@ -24,6 +24,7 @@ import {
   sftpTransferCenterStore,
   useSftpTransferCenterBadge,
   useSftpTransferResuming,
+  useSftpTransferTask,
   type SftpTransferCenterSnapshot,
 } from "../application/state/sftpTransferCenterStore";
 import { transferRuntime } from "../application/state/sftp/transferRuntime";
@@ -47,28 +48,22 @@ const CLOSED_TRANSFER_CENTER_SNAPSHOT: SftpTransferCenterSnapshot = {
 };
 
 /**
- * Full transfer-center list only while the popover is open. When closed, the
- * getter always returns the same CLOSED snapshot so progress store notifies do
- * not re-render this TopTabs child (badge uses a separate stable subscription).
+ * Read the folder hierarchy only while open and only on lifecycle changes.
+ * Mounted rows subscribe to their own bytes; progress must not regroup/sort
+ * every folder or re-render the center and its TopTabs ancestor.
  */
 function useSftpTransferCenterWhenOpen(open: boolean): SftpTransferCenterSnapshot {
   const openRef = useRef(open);
   openRef.current = open;
   return useSyncExternalStore(
     (onStoreChange) => {
-      // Lifecycle + progress: when the popover is open the list must move with
-      // bytes; when closed getSnapshot returns a stable CLOSED constant so
-      // progress ticks are cheap no-ops for this subscriber.
-      const unsubLifecycle = sftpTransferCenterStore.subscribe(onStoreChange);
-      const unsubProgress = sftpTransferCenterStore.subscribeProgress(onStoreChange);
-      return () => {
-        unsubLifecycle();
-        unsubProgress();
-      };
+      const unsubscribeLifecycle = sftpTransferCenterStore.subscribe(onStoreChange);
+      const unsubscribeProgress = sftpTransferCenterStore.subscribeProgress(onStoreChange);
+      return () => { unsubscribeLifecycle(); unsubscribeProgress(); };
     },
     () => (
       openRef.current
-        ? sftpTransferCenterStore.getSnapshot()
+        ? sftpTransferCenterStore.getLifecycleSnapshot()
         : CLOSED_TRANSFER_CENTER_SNAPSHOT
     ),
     () => CLOSED_TRANSFER_CENTER_SNAPSHOT,
@@ -340,8 +335,74 @@ function formatTransferPathLine(task: Pick<TransferTask, "sourcePath" | "targetP
   return `${source} → ${target}`;
 }
 
+const TransferChildRow = React.memo(function TransferChildRow({ task: snapshotTask, compact = false, frozen = false }: {
+  task: TransferTask;
+  compact?: boolean;
+  frozen?: boolean;
+}) {
+  const liveTask = useSftpTransferTask(snapshotTask.id, snapshotTask);
+  const task = frozen ? snapshotTask : liveTask;
+  const { t } = useI18n();
+  const percent = getGlobalTransferProgressPercent(task);
+  const detail = formatChildByteProgress(task)
+    || (task.totalBytes > 0 ? `${percent.toFixed(0)}%` : t(statusLabelKey(task.status)));
+  if (!compact) {
+    return (
+      <div className="flex h-6 items-center gap-2 rounded px-1 text-[10px] hover:bg-muted/40" data-transfer-status={task.status}>
+        <TruncatedTextWithTooltip text={task.fileName} tooltip={task.targetPath || task.fileName} className="flex-1 text-muted-foreground" />
+        <span className="shrink-0 font-mono text-muted-foreground">{detail}</span>
+        {task.status === "transferring" && <Loader2 size={10} className="shrink-0 animate-spin text-primary" />}
+      </div>
+    );
+  }
+  const childFrozen = frozen || task.status === "pausing" || task.status === "paused";
+  return (
+    <div className="min-w-0">
+      <div className="flex items-center justify-between gap-2 text-[10px] text-muted-foreground">
+        <TruncatedTextWithTooltip text={task.fileName} className="flex-1 text-muted-foreground" />
+        <span className="shrink-0 font-mono">{detail}</span>
+      </div>
+      {task.totalBytes > 0 && (
+        <div className="mt-0.5 h-1 overflow-hidden rounded-full bg-secondary">
+          <div className={cn("h-full rounded-full", task.status === "completed" ? "bg-emerald-500/80" : childFrozen ? "bg-amber-500/80" : "bg-primary/80")}
+            style={{ width: `${task.status === "completed" ? 100 : percent}%` }} />
+        </div>
+      )}
+    </div>
+  );
+});
+
+const TransferChildrenList = React.memo(function TransferChildrenList({ tasks }: { tasks: readonly TransferTask[] }) {
+  const scrollRef = useRef<HTMLDivElement>(null);
+  const virtual = tasks.length > 20;
+  const virtualizer = useVirtualizer({
+    count: tasks.length,
+    getScrollElement: () => scrollRef.current,
+    estimateSize: () => 24,
+    getItemKey: (index) => tasks[index].id,
+    initialRect: { width: 0, height: 192 },
+    overscan: 4,
+    enabled: virtual,
+  });
+  return (
+    <div className="mt-2 border-t border-border/40 pt-2">
+      <div ref={scrollRef} className="max-h-48 overflow-y-auto" style={{ height: Math.min(tasks.length, 8) * 24 }} data-section="global-sftp-transfer-child-list">
+        {!virtual ? tasks.map((task) => <TransferChildRow key={task.id} task={task} />) : (
+          <div className="relative w-full" style={{ height: virtualizer.getTotalSize() }}>
+            {virtualizer.getVirtualItems().map((row) => (
+              <div key={row.key} className="absolute left-0 top-0 w-full" style={{ transform: `translateY(${row.start}px)` }}>
+                <TransferChildRow task={tasks[row.index]} />
+              </div>
+            ))}
+          </div>
+        )}
+      </div>
+    </div>
+  );
+});
+
 function TransferRow({
-  task,
+  task: snapshotTask,
   childTasks = [],
   expanded,
   onToggleExpanded,
@@ -353,6 +414,7 @@ function TransferRow({
   onToggleExpanded: () => void;
   isLast: boolean;
 }) {
+  const task = useSftpTransferTask(snapshotTask.id, snapshotTask);
   const { t } = useI18n();
   const folderReplaceWarningId = React.useId();
   // Optimistic spinner from click until store status moves off paused/interrupted.
@@ -605,72 +667,14 @@ function TransferRow({
           )}
           data-section="global-sftp-transfer-active-children"
         >
-          {displayChildren.map((child) => {
-            const childPercent = getGlobalTransferProgressPercent(child);
-            const childDetail = formatChildByteProgress(child);
-            const childFrozen = isPausing
-              || task.status === "paused"
-              || child.status === "pausing"
-              || child.status === "paused";
-            return (
-              <div key={child.id} className="min-w-0">
-                <div className="flex items-center justify-between gap-2 text-[10px] text-muted-foreground">
-                  <TruncatedTextWithTooltip text={child.fileName} className="flex-1 text-muted-foreground" />
-                  <span className="shrink-0 font-mono">
-                    {childDetail || (child.totalBytes > 0 ? `${childPercent.toFixed(0)}%` : t(statusLabelKey(child.status)))}
-                  </span>
-                </div>
-                {child.totalBytes > 0 && (
-                  <div className="mt-0.5 h-1 overflow-hidden rounded-full bg-secondary">
-                    <div
-                      className={cn(
-                        "h-full rounded-full",
-                        child.status === "completed"
-                          ? "bg-emerald-500/80"
-                          : childFrozen
-                            ? "bg-amber-500/80"
-                            : "bg-primary/80",
-                      )}
-                      style={{ width: `${child.status === "completed" ? 100 : childPercent}%` }}
-                    />
-                  </div>
-                )}
-              </div>
-            );
-          })}
+          {displayChildren.map((child) => (
+            <TransferChildRow key={child.id} task={child} compact frozen={isPausing || task.status === "paused"} />
+          ))}
         </div>
       )}
 
       {isDirParent && expanded && childTasks.length > 0 && (
-        <div
-          className="mt-2 max-h-48 space-y-1 overflow-y-auto border-t border-border/40 pt-2"
-          data-section="global-sftp-transfer-child-list"
-        >
-          {childTasks.map((child) => {
-            const childPercent = getGlobalTransferProgressPercent(child);
-            const childDetail = formatChildByteProgress(child);
-            return (
-              <div
-                key={child.id}
-                className="flex items-center gap-2 rounded px-1 py-1 text-[10px] hover:bg-muted/40"
-                data-transfer-status={child.status}
-              >
-                <TruncatedTextWithTooltip
-                  text={child.fileName}
-                  tooltip={child.targetPath || child.fileName}
-                  className="flex-1 text-muted-foreground"
-                />
-                <span className="shrink-0 font-mono text-muted-foreground">
-                  {childDetail
-                    || (child.totalBytes > 0 ? `${childPercent.toFixed(0)}%` : t(statusLabelKey(child.status)))}
-                </span>
-                {child.status === "transferring" && (
-                  <Loader2 size={10} className="shrink-0 animate-spin text-primary" />
-                )}
-              </div>
-            );
-          })}
-        </div>
+        <TransferChildrenList tasks={childTasks} />
       )}
 
       {task.status === "attention" && task.conflict && canControl && (() => {

components/GlobalSftpTransferCenter.virtualization.test.tsx

@@ -1,7 +1,7 @@
 import assert from "node:assert/strict";
 import test from "node:test";
 import React from "react";
-import { createDomRenderer, dispatchDomEvent, flushEffects, installDomEnvironment } from "./test-support/renderReactDom.tsx";
+import { createDomRenderer, dispatchDomEvent, flushEffects, installDomEnvironment, runWithAct } from "./test-support/renderReactDom.tsx";
 
 test("large transfer histories mount only visible rows and can scroll to the last file", async (t) => {
   const env = installDomEnvironment();
@@ -64,6 +64,33 @@ test("large transfer histories mount only visible rows and can scroll to the las
   const lastRow = env.document.querySelector('[role=progressbar][aria-label="file-0.bin"]')?.closest('[data-transfer-status]');
   assert.ok(lastRow?.classList.contains("border-b-0"), "only the actual final row omits its divider");
   assert.equal(store.getSnapshot().tasks.length, 1_000, "offscreen files must remain queued");
+  await runWithAct(() => {
+    store.patchTask("virtual-file-999", { isDirectory: true, progressMode: "files" });
+    store.upsertTasks(Array.from({ length: 100 }, (_, index) => ({
+      id: `nested-file-${index}`, fileName: `nested-${index}.bin`,
+      sourcePath: `/source/999/${index}`, targetPath: `/target/999/${index}`,
+      sourceConnectionId: "source", targetConnectionId: "local", direction: "download" as const,
+      status: "queued" as const, totalBytes: 1_000, transferredBytes: 0, speed: 0,
+      startTime: index + 2_000, isDirectory: false, parentTaskId: "virtual-file-999",
+    })));
+  });
+  scroll.scrollTop = 0;
+  await dispatchDomEvent(scroll, new env.window.Event("scroll"));
+  await flushEffects();
+  const expand = env.document.querySelector('button[aria-label="Show files"]');
+  assert.ok(expand);
+  await dispatchDomEvent(expand, new env.window.MouseEvent("click", { bubbles: true }));
+  await flushEffects();
+  assert.ok(env.document.querySelector('[data-section="global-sftp-transfer-child-list"]'));
+  scroll.scrollTop = 112 * 1_000 - 460;
+  await dispatchDomEvent(scroll, new env.window.Event("scroll"));
+  await flushEffects();
+  scroll.scrollTop = 0;
+  await dispatchDomEvent(scroll, new env.window.Event("scroll"));
+  await flushEffects();
+  assert.ok(env.document.querySelector('button[aria-label="Hide files"]'), "folder expansion survives top-level row recycling");
+  assert.ok(env.document.querySelector('[data-section="global-sftp-transfer-child-list"]'));
+
   await dispatchDomEvent(toggle, new env.window.MouseEvent("click", { bubbles: true }));
   await flushEffects();
 });

docs/research/sftp-folder-list-performance.md

@@ -0,0 +1,96 @@
+# Expanded SFTP folder-list responsiveness
+
+The global transfer center already limited mounted top-level rows, but expanding
+a folder rendered every retained child file. Each progress update also rebuilt
+all folder groups and sorted their children. A folder with thousands of queued
+files therefore stalled the renderer even when only one file's bytes changed.
+
+The child list now mounts its visible range with a small overscan. Its existing
+scroll area still reaches every retained file. The transfer center reads a stable
+hierarchy snapshot between lifecycle changes; mounted parent/child rows subscribe
+to their own live progress. Progress that introduces a row or changes its status
+still refreshes the hierarchy. Completion retention and compact checkpoints are
+unchanged.
+
+## Controlled measurements
+
+A separate Electron window mounted the actual before/after transfer center with
+two synthetic directory transfers. No SSH connection, real file or user transfer
+was involved. The same expand action, ten updates to one child and a scroll to
+the final file were exercised in each version.
+
+| Children | Work | Before | After |
+| ---: | --- | ---: | ---: |
+| 1,000 | Expand to next rendered frame | 298.8 ms | 10.94 ms |
+| 1,000 | One child's progress to next frame | 112.6–125.6 ms | 1.18–18.18 ms |
+| 5,000 | Expand to next rendered frame | 1,216.1 ms | 14.36 ms |
+| 5,000 | One child's progress to next frame | 500.5–538.4 ms | 1.31–6.03 ms |
+| 1,000 / 5,000 | Mounted child rows | 1,000 / 5,000 | 12 / 12 |
+
+Both repaired lists reached their final child and retained all 1,000 / 5,000
+queued records. Native scrolling, collapse/reopen and live byte display were
+also checked. These are development-fixture measurements on one machine, not a
+cross-device frame-rate guarantee.
+
+The actual-component regression fails on the original implementation because
+it mounts 1,000 children. It verifies bounded mounted rows, live progress without
+re-sorting the folder, final-child access, completion accounting and collapse /
+reopen. The existing top-level recycling test also expands a folder, scrolls it
+out of view and returns to its retained expansion state.
+
+## Issue relationship
+
+Related to #3155. Its Windows report and subsequent comments cover multiple
+possible large-transfer failures; they do not establish that this exact expanded
+folder-list workload caused the reporter's freeze. This repair is independently
+reproduced UI work and must not close that issue. Open #3694 and #3696 modify
+file metadata / transfer connection acquisition, not this list behavior.
+
+## Control availability follow-up
+
+Independent review found that the initial stable snapshot did not refresh when
+progress reported a transfer could no longer pause, including a child's change
+propagated to its folder. Metadata-only patches and a newly available failed
+transfer checkpoint could similarly leave batch buttons stale. The list now
+refreshes its lightweight snapshot only when grouping/order/control eligibility
+fields change; repeated identical capability metadata on byte ticks keeps the
+hierarchy stable.
+
+The actual-component regression first failed with Pause all incorrectly enabled
+after the backend reported the folder could not pause. It now covers that child /
+parent update, direct metadata changes, repeated unchanged metadata without a
+full sort, and Resume all becoming available when a failed task gains a checkpoint.
+An Electron comparison against initial repair 1b96e27b0 confirmed stale batch
+buttons before and correct disabled/enabled states afterward. The final 1,000 /
+5,000 file runs still mounted 12 rows and reached the final file: expand-to-frame
+12.6 / 12.86 ms, child progress 1.32–15.42 / 1.06–17.90 ms.
+
+
+## Hierarchy repair follow-up
+
+A same-byte background event can repair a formerly top-level child before the
+progress de-duplication guard returns. The repaired hierarchy must be published
+even when the remaining event is ignored, including late events for terminal
+rows. Those early exits now publish only when repair actually replaced the row;
+normal progress still builds at most one hierarchy snapshot and ordinary byte
+ticks keep its reference stable.
+
+Both the store and actual-center regressions failed before this repair. The
+Electron comparison against e894c9cb confirmed the old folder had no Show files
+action after the same-byte event or its next byte tick. The repaired folder
+immediately exposes its child, and the next byte tick keeps that grouping
+without rebuilding it. A fresh 5,000-file run mounted 12 rows, reached the final
+file and retained all 5,000 records: expansion 14.12 ms, progress 1.28-18.58 ms.
+
+
+The repaired hierarchy also uses the existing coalesced persistence scheduler
+at the structural mutation, so an ignored terminal event cannot leave the old
+orphan on disk indefinitely. A restart regression first failed with zero writes
+for the repair; completed, failed and cancelled cases now each save the change
+once, restore under the folder (completed children through the existing compact
+checkpoint), and schedule no further writes on unchanged late progress. Owner
+lifecycle notifications stay at zero. An isolated actual Electron renderer
+compared 744f0f8e against the repair and confirmed all three old orphan restores
+and all three repaired restores. This run used synthetic in-memory persistence;
+manual window input was unavailable because macOS was locked. Earlier native
+folder scrolling and appearance evidence remains separate.