diff --git a/apps/web/src/components/files/FileBrowserPanel.browser.test.tsx b/apps/web/src/components/files/FileBrowserPanel.browser.test.tsx
index c7456f141c3b4..095a80a1726f6 100644
--- a/apps/web/src/components/files/FileBrowserPanel.browser.test.tsx
+++ b/apps/web/src/components/files/FileBrowserPanel.browser.test.tsx
@@ -1,4 +1,5 @@
 import { EnvironmentId, type ProjectEntry } from "@t3tools/contracts";
+import { FileTree } from "@pierre/trees";
 import { describe, expect, it, vi } from "vite-plus/test";
 import { page, userEvent } from "vite-plus/test/browser";
 
@@ -16,7 +17,7 @@ const entries: readonly ProjectEntry[] = [
 const loadingDirectories: ReadonlySet<string> = new Set();
 const directory: {
   entries: readonly ProjectEntry[];
-  load: () => Promise<void>;
+  load: (path: string) => Promise<void>;
   refresh: () => void;
   ready: boolean;
   error: null;
@@ -24,7 +25,7 @@ const directory: {
   loadingDirectories: ReadonlySet<string>;
 } = {
   entries,
-  load: () => Promise.resolve(),
+  load: (_path) => Promise.resolve(),
   refresh: () => {},
   ready: true,
   error: null,
@@ -54,15 +55,24 @@ function findTreeRow(path: string): HTMLElement | null {
   return null;
 }
 
-function withDirectoryListing(listing: readonly ProjectEntry[]): Disposable {
+function withDirectoryListing(
+  listing: readonly ProjectEntry[],
+  load: typeof directory.load = directory.load,
+): Disposable {
+  const previousLoad = directory.load;
   directory.entries = listing;
+  directory.load = load;
   return {
     [Symbol.dispose]: () => {
       directory.entries = entries;
+      directory.load = previousLoad;
     },
   };
 }
 
+const folders = (count: number): ProjectEntry[] =>
+  Array.from({ length: count }, (_, index) => ({ path: `folder-${index}`, kind: "directory" }));
+
 describe("FileBrowserPanel", () => {
   it("copies with the pointer and returns to the row after keyboard dismissal", async () => {
     await using _screen = await render(
@@ -237,6 +247,64 @@ describe("FileBrowserPanel", () => {
     await expect.element(search).toHaveValue("generated-");
   });
 
+  it("expands every folder without asking the tree about all folders for each one", async () => {
+    const load = vi.fn((_path: string) => Promise.resolve());
+    using _listing = withDirectoryListing(folders(300), load);
+    await using _screen = await render(
+      <FileBrowserPanel
+        environmentId={EnvironmentId.make("env-files")}
+        cwd="/repo-expand-all-1"
+        projectName="repo"
+        selectedPath={null}
+        selectedPathRevealId={0}
+        onOpenFile={() => {}}
+        workspaceMutationId={null}
+      />,
+    );
+    using getItem = vi.spyOn(FileTree.prototype, "getItem");
+    const expandAll = page.getByRole("button", { name: "Expand all folders" });
+    await expect.element(expandAll).toBeVisible();
+    getItem.mockClear();
+    await userEvent.click(expandAll);
+    await expect.element(page.getByRole("button", { name: "Collapse all folders" })).toBeVisible();
+    await vi.waitFor(() => expect(load).toHaveBeenCalledTimes(300));
+    // Each of the 300 expansions used to look up all 300 folders again, about 137,000 lookups.
+    expect(getItem.mock.calls.length).toBeLessThan(300 * 20);
+  });
+
+  it("expands folders that arrive after Expand all without visiting the earlier ones again", async () => {
+    const batches = 5;
+    const perBatch = 60;
+    const load = vi.fn((_path: string) => Promise.resolve());
+    using _listing = withDirectoryListing(folders(perBatch), load);
+    const renderPanel = () => (
+      <FileBrowserPanel
+        environmentId={EnvironmentId.make("env-files")}
+        cwd="/repo-expand-all-2"
+        projectName="repo"
+        selectedPath={null}
+        selectedPathRevealId={0}
+        onOpenFile={() => {}}
+        workspaceMutationId={null}
+      />
+    );
+    await using screen = await render(renderPanel());
+    using getItem = vi.spyOn(FileTree.prototype, "getItem");
+    await userEvent.click(page.getByRole("button", { name: "Expand all folders" }));
+    await vi.waitFor(() => expect(load).toHaveBeenCalledTimes(perBatch));
+    getItem.mockClear();
+    for (let batch = 2; batch <= batches; batch++) {
+      directory.entries = folders(batch * perBatch);
+      await screen.rerender(renderPanel());
+      await vi.waitFor(() => expect(load).toHaveBeenCalledTimes(batch * perBatch));
+    }
+    await expect.element(page.getByRole("button", { name: "Collapse all folders" })).toBeVisible();
+    expect(new Set(load.mock.calls.map(([path]) => path)).size).toBe(batches * perBatch);
+    // About 1,100 lookups. Rescanning every folder for the button state adds about 5,000, and a
+    // second scan of every folder per listing about 800.
+    expect(getItem.mock.calls.length).toBeLessThan(1_400);
+  });
+
   it("mod+f from a tree row, or the panel find command, focuses the file search", async () => {
     await using _screen = await render(
       <FileBrowserPanel
diff --git a/apps/web/src/components/files/FileBrowserPanel.tsx b/apps/web/src/components/files/FileBrowserPanel.tsx
index 24912502fc355..abb1cda430342 100644
--- a/apps/web/src/components/files/FileBrowserPanel.tsx
+++ b/apps/web/src/components/files/FileBrowserPanel.tsx
@@ -4,13 +4,13 @@ import type {
   ContextMenuOpenContext as TreeContextMenuOpenContext,
 } from "@pierre/trees";
 import type { EnvironmentId, ProjectEntry } from "@t3tools/contracts";
-import { FileTree, useFileTree, useFileTreeSearch, useFileTreeSelector } from "@pierre/trees/react";
+import { FileTree, useFileTree, useFileTreeSearch } from "@pierre/trees/react";
 import { settlePromise } from "@t3tools/client-runtime/state/runtime";
 import { serializeComposerFileLink } from "@t3tools/shared/composerTrigger";
 import * as AsyncResult from "effect/reactivity/AsyncResult";
 import * as Cause from "effect/Cause";
 import { ChevronsDownUpIcon, ChevronsUpDownIcon } from "lucide-react";
-import { type Ref, useEffect, useEffectEvent, useRef, useState } from "react";
+import { type Ref, useEffect, useEffectEvent, useRef, useState, useSyncExternalStore } from "react";
 
 import { Button } from "~/components/ui/button";
 import { InputGroup, InputGroupInput } from "~/components/ui/input-group";
@@ -30,9 +30,9 @@ import { joinHostPath } from "./filePath";
 import { createFileTreeDragMentionController } from "./fileTreeDragMention";
 import {
   areAllDirectoriesExpanded,
-  coalesceReentrantCalls,
   readExpandedDirectories,
   setAllDirectoriesExpanded,
+  subscribeOncePerTask,
   writeExpandedDirectories,
 } from "./fileTreeExpansion";
 import { buildFileTreePathUpdates, shouldRebuildFileTree } from "./fileTreePathReconciliation";
@@ -314,8 +314,11 @@ export default function FileBrowserPanel({
   const search = useFileTreeSearch(model);
   // Pierre restores the unfiltered tree when a search has no matches.
   const hasNoSearchMatches = search.value.trim().length > 0 && search.matchingPaths.length === 0;
-  const allDirectoriesExpanded = useFileTreeSelector(model, (currentModel) =>
-    areAllDirectoriesExpanded(currentModel, expandableDirectoryPaths),
+  const allDirectoriesExpanded = useSyncExternalStore(
+    (listener) => subscribeOncePerTask(model, listener),
+    // The expand-all effect keeps every folder open, and collapsing one turns Expand all off.
+    () =>
+      (expandAll && !query.trim()) || areAllDirectoriesExpanded(model, expandableDirectoryPaths),
   );
   const toggleAllDirectories = () => {
     const expanded = !(expandAll || allDirectoriesExpanded);
@@ -345,20 +348,26 @@ export default function FileBrowserPanel({
     return subscribePreviewAction(onPanelAction);
   }, [answersPanelFind]);
   const expandedPathsRef = useRef(new Set<string>());
+  const expandedByExpandAllRef = useRef(new Set<string>());
   const expansionRoot = `${environmentId}:${cwd}`;
   // Folders expanded when the panel last unmounted; each reopens once lazy loading lists it.
   const [pendingExpandedPaths] = useState(() => new Set(readExpandedDirectories(expansionRoot)));
-  // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- subscribes to the Pierre tree model to load directories as they are expanded
+  const directoryPathsRef = useRef(directoryPaths);
+  // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- forgets expanded folders that left the listing before the Pierre tree model notifies about them
   useEffect(() => {
+    directoryPathsRef.current = directoryPaths;
     const currentPaths = new Set(directoryPaths);
     for (const path of expandedPathsRef.current) {
       if (!currentPaths.has(path)) expandedPathsRef.current.delete(path);
     }
-    // Restoring calls item.expand(), which notifies subscribers synchronously.
-    const loadExpanded = coalesceReentrantCalls(() => {
+  }, [directoryPaths]);
+  // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- subscribes to the Pierre tree model to load directories as they are expanded
+  useEffect(() => {
+    // Not rerun per listing: adding its paths to the model notifies this listener once.
+    const loadExpanded = () => {
       if (model.isSearchOpen()) return;
       let changed = false;
-      for (const path of directoryPaths) {
+      for (const path of directoryPathsRef.current) {
         const item = model.getItem(path);
         if (item?.isDirectory() && pendingExpandedPaths.delete(path) && "expand" in item) {
           item.expand();
@@ -380,10 +389,10 @@ export default function FileBrowserPanel({
           ...pendingExpandedPaths,
         ]);
       }
-    });
+    };
     loadExpanded();
-    return model.subscribe(loadExpanded);
-  }, [directoryPaths, expansionRoot, load, model, pendingExpandedPaths]);
+    return subscribeOncePerTask(model, loadExpanded);
+  }, [expansionRoot, load, model, pendingExpandedPaths]);
   // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- pushes ignored-file status into the imperative Pierre tree model
   useEffect(() => {
     model.setGitStatus(
@@ -451,8 +460,18 @@ export default function FileBrowserPanel({
 
   // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- expands every directory in the Pierre tree model while expand-all is on and no search is active
   useEffect(() => {
-    if (expandAll && !query.trim())
-      setAllDirectoriesExpanded(model, expandableDirectoryPaths, true);
+    if (!expandAll || query.trim()) {
+      expandedByExpandAllRef.current.clear();
+      return;
+    }
+    // Only folders listed since the last pass; asking the tree about every folder each time is quadratic.
+    const previous = expandedByExpandAllRef.current;
+    setAllDirectoriesExpanded(
+      model,
+      expandableDirectoryPaths.filter((path) => !previous.has(path)),
+      true,
+    );
+    expandedByExpandAllRef.current = new Set(expandableDirectoryPaths);
   }, [expandableDirectoryPaths, expandAll, model, query]);
 
   // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- reveals an externally selected path in the Pierre tree model by expanding, selecting and scrolling
diff --git a/apps/web/src/components/files/fileTreeExpansion.ts b/apps/web/src/components/files/fileTreeExpansion.ts
index 35e6a548603ee..2e0ca5b0631e0 100644
--- a/apps/web/src/components/files/fileTreeExpansion.ts
+++ b/apps/web/src/components/files/fileTreeExpansion.ts
@@ -35,6 +35,7 @@ function asDirectoryHandle(item: unknown): DirectoryHandle | null {
 /**
  * Calls `listener` once per task, however many events the model emitted in it. Expanding every
  * folder emits one event per folder, and a listener that rescans the folders is quadratic otherwise.
+ * Deferring also keeps a listener that expands items from rerunning inside itself.
  */
 export function subscribeOncePerTask(
   model: { subscribe(listener: () => void): () => void },
@@ -82,27 +83,6 @@ export function setAllDirectoriesExpanded(
   }
 }
 
-/** Calls made while `run` is running rerun it once it returns, instead of nesting. */
-export function coalesceReentrantCalls(run: () => void): () => void {
-  let running = false;
-  let calledAgain = false;
-  return () => {
-    if (running) {
-      calledAgain = true;
-      return;
-    }
-    running = true;
-    try {
-      do {
-        calledAgain = false;
-        run();
-      } while (calledAgain);
-    } finally {
-      running = false;
-    }
-  };
-}
-
 const EXPANDED_DIRECTORIES_STORAGE_KEY = "t3code.fileTreeExpandedDirectories";
 // Roots are kept most recent first and capped so worktrees that come and go do not grow storage.
 const MAX_STORED_ROOTS = 20;