diff --git a/packages/ui/src/components/Sidebar.test.tsx b/packages/ui/src/components/Sidebar.test.tsx
new file mode 100644
index 00000000..fe89ba20
--- /dev/null
+++ b/packages/ui/src/components/Sidebar.test.tsx
@@ -0,0 +1,158 @@
+// @vitest-environment happy-dom
+
+import { act, type ReactNode } from "react";
+// @ts-expect-error This package does not ship @types/react-dom; the test only
+// needs createRoot's render/unmount surface.
+import { createRoot } from "react-dom/client";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { Sidebar } from "./Sidebar";
+
+type Root = {
+	render(children: ReactNode): void;
+	unmount(): void;
+};
+
+const roots: Root[] = [];
+const expandedStorageKey = "hubble-sidebar-expanded-folders:test";
+
+(
+	globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }
+).IS_REACT_ACT_ENVIRONMENT = true;
+
+afterEach(() => {
+	act(() => {
+		for (const root of roots) root.unmount();
+	});
+	roots.length = 0;
+	localStorage.clear();
+	document.body.replaceChildren();
+	vi.restoreAllMocks();
+});
+
+describe("Sidebar folder clicks", () => {
+	it("selects an expanded folder before collapsing it on a second click", () => {
+		seedExpanded("project/");
+		const onSelectFile = vi.fn();
+		renderSidebar(onSelectFile);
+
+		clickRow("note.md");
+		expect(onSelectFile).toHaveBeenCalledWith("/workspace/project/note.md");
+
+		clickRow("project");
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("true");
+		expect(folderRow("project").getAttribute("aria-selected")).toBe("true");
+		expect(row("note.md")).not.toBeNull();
+
+		clickRow("project");
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("false");
+		expect(row("note.md")).toBeNull();
+		expect(onSelectFile).toHaveBeenCalledTimes(1);
+	});
+
+	it("expands a collapsed folder on the first row click", () => {
+		renderSidebar();
+
+		clickRow("archive");
+		expect(folderRow("archive").getAttribute("aria-expanded")).toBe("true");
+		expect(folderRow("archive").getAttribute("aria-selected")).toBe("true");
+		expect(row("old.md")).not.toBeNull();
+	});
+
+	it("keeps folders expanded after row and chevron double clicks", () => {
+		renderSidebar();
+
+		clickRow("archive");
+		clickRow("archive", { detail: 2 });
+		expect(folderRow("archive").getAttribute("aria-expanded")).toBe("true");
+
+		clickFolderToggle("project");
+		clickFolderToggle("project", { detail: 2 });
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("true");
+	});
+
+	it("collapses an expanded folder immediately from its chevron", () => {
+		seedExpanded("project/");
+		renderSidebar();
+
+		clickRow("note.md");
+		clickFolderToggle("project");
+
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("false");
+		expect(row("note.md")).toBeNull();
+	});
+
+	it("reduces a multi-selection before collapsing a folder", () => {
+		seedExpanded("project/", "archive/");
+		renderSidebar();
+
+		clickRow("project");
+		clickRow("archive", { ctrlKey: true });
+		expect(folderRow("archive").getAttribute("aria-expanded")).toBe("true");
+
+		clickRow("project");
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("true");
+		expect(folderRow("archive").getAttribute("aria-selected")).toBe("false");
+
+		clickRow("project");
+		expect(folderRow("project").getAttribute("aria-expanded")).toBe("false");
+	});
+});
+
+function seedExpanded(...folderIds: string[]) {
+	localStorage.setItem(expandedStorageKey, JSON.stringify(folderIds));
+}
+
+function renderSidebar(onSelectFile: (path: string) => void = () => {}) {
+	const container = document.createElement("div");
+	document.body.append(container);
+	const root = createRoot(container);
+	roots.push(root);
+	act(() => {
+		root.render(
+			<Sidebar
+				files={[
+					{ path: "/workspace/project/note.md" },
+					{ path: "/workspace/archive/old.md" },
+				]}
+				currentPath={null}
+				getDisplayPath={(path) => path.replace("/workspace/", "")}
+				onSelectFile={onSelectFile}
+				onSortModeChange={() => {}}
+				sortMode="alpha"
+				storageScope="test"
+			/>,
+		);
+	});
+}
+
+function row(label: string) {
+	return document.querySelector<HTMLElement>(
+		`[role="treeitem"][title="${label}"]`,
+	);
+}
+
+function folderRow(label: string) {
+	const element = row(label);
+	if (!element) throw new Error(`Missing folder row ${label}`);
+	return element;
+}
+
+function clickRow(label: string, init: MouseEventInit = {}) {
+	const button = row(label)?.querySelector("button");
+	if (!button) throw new Error(`Missing row button ${label}`);
+	dispatchClick(button, init);
+}
+
+function clickFolderToggle(label: string, init: MouseEventInit = {}) {
+	const toggle = row(label)?.querySelector("[data-sidebar-folder-toggle]");
+	if (!toggle) throw new Error(`Missing folder toggle ${label}`);
+	dispatchClick(toggle, init);
+}
+
+function dispatchClick(target: Element, init: MouseEventInit) {
+	act(() => {
+		target.dispatchEvent(
+			new MouseEvent("click", { bubbles: true, detail: 1, ...init }),
+		);
+	});
+}
diff --git a/packages/ui/src/components/Sidebar.tsx b/packages/ui/src/components/Sidebar.tsx
index f7164ec5..4533236f 100644
--- a/packages/ui/src/components/Sidebar.tsx
+++ b/packages/ui/src/components/Sidebar.tsx
@@ -585,6 +585,12 @@ export function Sidebar({
 		row: SidebarSelectableRow,
 		event: React.MouseEvent<HTMLButtonElement>,
 	) => {
+		const rowKey = sidebarRowKey(row);
+		const wasOnlySelectedRow =
+			rowKey !== null && selectedKeys.size === 1 && selectedKeys.has(rowKey);
+		const clickedFolderToggle =
+			event.target instanceof Element &&
+			event.target.closest("[data-sidebar-folder-toggle]") !== null;
 		const mode: SidebarSelectionMode = event.shiftKey
 			? "range"
 			: event.metaKey || event.ctrlKey
@@ -595,8 +601,12 @@ export function Sidebar({
 			event.preventDefault();
 			return;
 		}
-		if (row.kind === "file" && event.detail > 1) return;
-		activateRow(row);
+		if (event.detail > 1) return;
+		// Expanded folders select first; the chevron toggles immediately.
+		const wouldCollapseFolder = row.kind === "folder" && row.expanded;
+		if (!wouldCollapseFolder || clickedFolderToggle || wasOnlySelectedRow) {
+			activateRow(row);
+		}
 		requestAnimationFrame(() => navRef.current?.focus());
 	};
 	const enterRowEdit = (row: SidebarRow) => {
@@ -957,7 +967,12 @@ export function Sidebar({
 						paddingInlineStart: `${0.5 + row.depth * 0.75}rem`,
 					} as React.CSSProperties;
 					const chevron = (
-						<span className="inline-flex size-3 shrink-0 items-center justify-center text-muted-foreground">
+						<span
+							className="-m-1 inline-flex size-5 shrink-0 items-center justify-center text-muted-foreground"
+							data-sidebar-folder-toggle={
+								row.kind === "folder" ? "" : undefined
+							}
+						>
 							{row.kind === "folder" && (
 								<MingcuteRightLine
 									className={cn(
@@ -1001,7 +1016,8 @@ export function Sidebar({
 									data-selected={isSelected ? "true" : undefined}
 									className={cn(
 										"group/sidebar-row relative flex w-full items-center text-sidebar-foreground",
-										"transition-[background-color,opacity,filter] duration-150 ease-out motion-reduce:transition-none",
+										// Background transitions leave a ghost highlight when expansion reorders rows.
+										"transition-[opacity,filter] duration-150 ease-out motion-reduce:transition-none",
 										isSelected &&
 											"bg-sidebar-accent text-sidebar-accent-foreground",
 										isOpen && "font-medium",