diff --git a/docs/assets/javascripts/sidebar-toggle.js b/docs/assets/javascripts/sidebar-toggle.js
new file mode 100644
index 00000000..9e12d149
--- /dev/null
+++ b/docs/assets/javascripts/sidebar-toggle.js
@@ -0,0 +1,101 @@
+(function () {
+  "use strict";
+
+  const storageKey = "dg-sidebar-collapsed";
+  const desktopQuery = "(min-width: 1220px)";
+
+  function readStoredState(storage) {
+    if (!storage) return false;
+    try {
+      return storage.getItem(storageKey) === "true";
+    } catch {
+      return false;
+    }
+  }
+
+  function writeStoredState(storage, collapsed) {
+    if (!storage) return;
+    try {
+      storage.setItem(storageKey, collapsed ? "true" : "false");
+    } catch {
+      // Ignore storage failures (private mode / strict policies).
+    }
+  }
+
+  function getStorage(windowRef) {
+    try {
+      return windowRef.localStorage || null;
+    } catch {
+      return null;
+    }
+  }
+
+  function applyState(root, button, storage, collapsed) {
+    root.dataset.dgSidebarCollapsed = collapsed ? "true" : "false";
+    button.setAttribute("aria-expanded", collapsed ? "false" : "true");
+    button.setAttribute("aria-label", "왼쪽 메뉴");
+    writeStoredState(storage, collapsed);
+  }
+
+  function mountSidebarToggle(documentRef, windowRef) {
+    if (!documentRef || !windowRef) return null;
+    const root = documentRef.documentElement;
+    if (!root || root.dataset.dgSidebarToggleReady === "true") return null;
+    const headerInner = documentRef.querySelector(".md-header__inner");
+    if (!headerInner) return null;
+
+    root.dataset.dgSidebarToggleReady = "true";
+
+    const button = documentRef.createElement("button");
+    button.type = "button";
+    button.className = "md-header__button md-icon dg-sidebar-toggle";
+    button.setAttribute("aria-expanded", "true");
+    button.setAttribute("aria-label", "왼쪽 메뉴");
+    button.title = "왼쪽 메뉴 접기/펼치기";
+    button.innerHTML =
+      '<svg viewBox="0 0 24 24" role="presentation" focusable="false"><path d="M3 6h18v2H3V6zm0 5h18v2H3v-2zm0 5h18v2H3v-2z"/></svg>';
+
+    const mediaQuery = typeof windowRef.matchMedia === "function"
+      ? windowRef.matchMedia(desktopQuery)
+      : null;
+    const storage = getStorage(windowRef);
+
+    const syncState = () => {
+      const collapsed = readStoredState(storage);
+      applyState(root, button, storage, collapsed);
+    };
+
+    button.addEventListener("click", () => {
+      const collapsed = root.dataset.dgSidebarCollapsed === "true";
+      applyState(root, button, storage, !collapsed);
+    });
+
+    if (mediaQuery) {
+      const onMediaChange = event => {
+        if (event.matches) syncState();
+      };
+      if (typeof mediaQuery.addEventListener === "function") {
+        mediaQuery.addEventListener("change", onMediaChange);
+      } else if (typeof mediaQuery.addListener === "function") {
+        mediaQuery.addListener(onMediaChange);
+      }
+    }
+
+    syncState();
+    headerInner.insertBefore(button, headerInner.firstChild);
+    return button;
+  }
+
+  if (typeof module !== "undefined" && module.exports) {
+    module.exports = {mountSidebarToggle, readStoredState, applyState, getStorage};
+  }
+
+  if (typeof document !== "undefined") {
+    const start = () => mountSidebarToggle(document, window);
+    if (document.readyState === "loading") {
+      document.addEventListener("DOMContentLoaded", start);
+    } else {
+      start();
+    }
+  }
+})();
diff --git a/docs/assets/stylesheets/extra.css b/docs/assets/stylesheets/extra.css
index 36dae0db..66e8a6b9 100644
--- a/docs/assets/stylesheets/extra.css
+++ b/docs/assets/stylesheets/extra.css
@@ -286,7 +286,37 @@ body {
   box-shadow: inset 2px 0 var(--dg-accent);
 }
 
+.dg-sidebar-toggle {
+  display: none;
+}
+
+@media (max-width: 1219px) {
+  .md-header .dg-sidebar-toggle {
+    display: none !important;
+  }
+}
+
 @media (min-width: 1220px) {
+  .md-header .dg-sidebar-toggle {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+  }
+
+  .dg-sidebar-toggle svg {
+    width: 1.1rem;
+    height: 1.1rem;
+    fill: currentColor;
+  }
+
+  [data-dg-sidebar-collapsed="true"] .md-sidebar--primary {
+    display: none;
+  }
+
+  [data-dg-sidebar-collapsed="true"] .dg-sidebar-toggle {
+    color: var(--dg-accent);
+  }
+
   .md-nav--primary .md-nav[data-md-level="1"],
   .md-nav--primary .md-nav[data-md-level="2"] {
     border-left: 1px solid var(--dg-border);
diff --git a/mkdocs.yml b/mkdocs.yml
index 73df1196..ecf9af16 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -82,5 +82,6 @@ extra_css:
 
 extra_javascript:
   - assets/javascripts/explore.js
+  - assets/javascripts/sidebar-toggle.js
 
 copyright: Copyright &copy; Azure Engineering Notes contributors
diff --git a/tests/docs/sidebar-toggle.test.cjs b/tests/docs/sidebar-toggle.test.cjs
new file mode 100644
index 00000000..f20c0e2e
--- /dev/null
+++ b/tests/docs/sidebar-toggle.test.cjs
@@ -0,0 +1,114 @@
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const toggle = require("../../docs/assets/javascripts/sidebar-toggle.js");
+
+function createFixture(stored = "false") {
+  const root = {dataset: {}};
+  const buttonListeners = {};
+  const inserted = [];
+
+  const button = {
+    attributes: {},
+    type: "",
+    className: "",
+    title: "",
+    innerHTML: "",
+    setAttribute(name, value) {
+      this.attributes[name] = value;
+    },
+    addEventListener(type, callback) {
+      buttonListeners[type] = callback;
+    },
+  };
+
+  const headerInner = {
+    firstChild: null,
+    insertBefore(node) {
+      inserted.push(node);
+    },
+  };
+
+  const localStorage = {
+    value: stored,
+    getItem() {
+      return this.value;
+    },
+    setItem(_key, value) {
+      this.value = value;
+    },
+  };
+
+  const media = {
+    matches: true,
+    addEventListener() {},
+  };
+
+  const documentRef = {
+    documentElement: root,
+    querySelector(selector) {
+      return selector === ".md-header__inner" ? headerInner : null;
+    },
+    createElement(tag) {
+      assert.equal(tag, "button");
+      return button;
+    },
+  };
+
+  const windowRef = {
+    localStorage,
+    matchMedia() {
+      return media;
+    },
+  };
+
+  return {
+    root,
+    button,
+    buttonListeners,
+    inserted,
+    documentRef,
+    windowRef,
+    localStorage,
+    media,
+  };
+}
+
+test("mountSidebarToggle inserts a button and applies stored collapsed state", () => {
+  const fixture = createFixture("true");
+  const mounted = toggle.mountSidebarToggle(fixture.documentRef, fixture.windowRef);
+  assert.equal(mounted, fixture.button);
+  assert.equal(fixture.inserted.length, 1);
+  assert.equal(fixture.root.dataset.dgSidebarCollapsed, "true");
+  assert.equal(fixture.button.attributes["aria-expanded"], "false");
+  assert.equal(fixture.button.attributes["aria-label"], "왼쪽 메뉴");
+  assert.equal(fixture.button.attributes["aria-pressed"], undefined);
+  assert.equal(fixture.root.dataset.dgSidebarToggleReady, "true");
+});
+
+test("button click toggles collapsed state and persists to storage", () => {
+  const fixture = createFixture("false");
+  toggle.mountSidebarToggle(fixture.documentRef, fixture.windowRef);
+  fixture.buttonListeners.click();
+  assert.equal(fixture.root.dataset.dgSidebarCollapsed, "true");
+  assert.equal(fixture.button.attributes["aria-expanded"], "false");
+  assert.equal(fixture.localStorage.value, "true");
+  fixture.buttonListeners.click();
+  assert.equal(fixture.root.dataset.dgSidebarCollapsed, "false");
+  assert.equal(fixture.button.attributes["aria-expanded"], "true");
+  assert.equal(fixture.localStorage.value, "false");
+});
+
+test("blocked localStorage still mounts without persistence", () => {
+  const fixture = createFixture("true");
+  Object.defineProperty(fixture.windowRef, "localStorage", {
+    get() {
+      throw new Error("storage blocked");
+    },
+  });
+  const mounted = toggle.mountSidebarToggle(fixture.documentRef, fixture.windowRef);
+  assert.equal(mounted, fixture.button);
+  assert.equal(fixture.inserted.length, 1);
+  assert.equal(fixture.root.dataset.dgSidebarCollapsed, "false");
+  fixture.buttonListeners.click();
+  assert.equal(fixture.root.dataset.dgSidebarCollapsed, "true");
+});
diff --git a/tests/docs/test_faceted_discovery.py b/tests/docs/test_faceted_discovery.py
index 549c95a1..df1565e1 100644
--- a/tests/docs/test_faceted_discovery.py
+++ b/tests/docs/test_faceted_discovery.py
@@ -261,11 +261,12 @@ def test_service_discovery_reports_topics_and_documents(taxonomy, catalog):
         assert "개 주제 · " in pages[PurePosixPath(path)]
 
 
-def test_javascript_behavior_with_available_node():
+@pytest.mark.parametrize("script_name", ("explore.test.cjs", "sidebar-toggle.test.cjs"))
+def test_javascript_behavior_with_available_node(script_name):
     node = shutil.which("node")
     if not node:
         pytest.skip("Node unavailable: parent browser verification is required")
-    result = subprocess.run([node, "--test", str(ROOT / "tests/docs/explore.test.cjs")],
+    result = subprocess.run([node, "--test", str(ROOT / "tests/docs" / script_name)],
                             cwd=ROOT, capture_output=True, text=True)
     assert result.returncode == 0, result.stdout + result.stderr