Remember nav section collapsed state

app/javascript/controllers/nav_section_expander_controller.js

@@ -0,0 +1,26 @@
+import { Controller } from "@hotwired/stimulus"
+
+export default class extends Controller {
+  static values = { key: String }
+
+  connect() {
+    this.#restoreToggle()
+  }
+
+  toggle() {
+    if (this.element.open) {
+      localStorage.removeItem(this.#localStorageKey)
+    } else {
+      localStorage.setItem(this.#localStorageKey, this.keyValue)
+    }
+  }
+
+  #restoreToggle() {
+    const isCollapsed = localStorage.getItem(this.#localStorageKey) != null
+    if (isCollapsed) this.element.open = false
+  }
+
+  get #localStorageKey() {
+    return this.keyValue
+  }
+}