feat: add sidebar view switcher dropdown in fullscreen mode (task-10)

- HTML: Replace .sidebar-title in sidebar-header with a view dropdown
  containing #sidebar-view-dropdown-trigger and #sidebar-view-dropdown-menu
- JS: Add renderSidebarViewDropdown() for populating sidebar menu (no action buttons)
- JS: Add toggleSidebarViewDropdown() for open/close with aria-expanded
- JS: Update switchView() to also update #sidebar-view-label in sidebar
- JS: Bind sidebar trigger click and delegated menu click in bindStaticEventListeners()
- CSS: Add .sidebar-view-dropdown, .sidebar-view-trigger, .sidebar-view-trigger:hover,
  and #sidebar-view-dropdown-menu position overrides
- Tests: Add test_sidebar_view_dropdown_exists and test_sidebar_view_dropdown_menu_exists
- Tests: Update test_html_session_sidebar_structure to reflect new dropdown structure

muxplex/frontend/app.js

@@ -898,6 +898,62 @@ function closeViewDropdown() {
   if (trigger) trigger.setAttribute('aria-expanded', 'false');
 }
 
+/**
+ * Render the sidebar view dropdown menu (same data as the header dropdown,
+ * but no action buttons — navigation only).
+ */
+function renderSidebarViewDropdown() {
+  var menu = $('sidebar-view-dropdown-menu');
+  if (!menu) return;
+
+  var views = (_serverSettings && _serverSettings.views) || [];
+  var hidden = (_serverSettings && _serverSettings.hidden_sessions) || [];
+  var hiddenCount = hidden.length;
+
+  var html = '';
+
+  // — All Sessions (always first)
+  var allActive = _activeView === 'all' ? ' view-dropdown-item--active' : '';
+  html += '<button class="view-dropdown-item' + allActive + '" data-view="all"><span class="view-dropdown-shortcut">1</span> All Sessions</button>';
+
+  // — User views
+  if (views.length > 0) {
+    html += '<div class="view-dropdown-separator"></div>';
+    for (var i = 0; i < views.length && i < 7; i++) {
+      var v = views[i];
+      var vActive = _activeView === v.name ? ' view-dropdown-item--active' : '';
+      html += '<button class="view-dropdown-item' + vActive + '" data-view="' + escapeHtml(v.name) + '"><span class="view-dropdown-shortcut">' + (i + 2) + '</span> ' + escapeHtml(v.name) + '</button>';
+    }
+  }
+
+  // — Hidden (N) (always last system view)
+  html += '<div class="view-dropdown-separator"></div>';
+  var hiddenActive = _activeView === 'hidden' ? ' view-dropdown-item--active' : '';
+  html += '<button class="view-dropdown-item' + hiddenActive + '" data-view="hidden"><span class="view-dropdown-shortcut">9</span> Hidden <span class="view-dropdown-badge">' + hiddenCount + '</span></button>';
+
+  menu.innerHTML = html;
+}
+
+/**
+ * Toggle the sidebar view dropdown open/closed.
+ * Calls renderSidebarViewDropdown() when opening to ensure fresh content.
+ */
+function toggleSidebarViewDropdown() {
+  var menu = $('sidebar-view-dropdown-menu');
+  var trigger = $('sidebar-view-dropdown-trigger');
+  if (!menu) return;
+
+  var isOpen = !menu.classList.contains('hidden');
+  if (isOpen) {
+    menu.classList.add('hidden');
+    if (trigger) trigger.setAttribute('aria-expanded', 'false');
+  } else {
+    menu.classList.remove('hidden');
+    if (trigger) trigger.setAttribute('aria-expanded', 'true');
+    renderSidebarViewDropdown();
+  }
+}
+
 /**
  * Show an inline text input inside the view dropdown for creating a new view.
  * Replaces the '+ New View' button with a text input inside the dropdown menu.
@@ -1235,6 +1291,17 @@ function switchView(viewName) {
   renderGrid(_currentSessions || []);
   renderSidebar(_currentSessions || [], _viewingSession);
   renderViewDropdown();
+  // Update sidebar view label to match the active view
+  var sidebarLabel = $('sidebar-view-label');
+  if (sidebarLabel) {
+    if (viewName === 'all') {
+      sidebarLabel.textContent = 'All Sessions';
+    } else if (viewName === 'hidden') {
+      sidebarLabel.textContent = 'Hidden';
+    } else {
+      sidebarLabel.textContent = viewName;
+    }
+  }
   // Persist active view — fire and forget
   api('PATCH', '/api/state', { active_view: viewName }).catch(function() {});
 }
@@ -2777,6 +2844,23 @@ function bindStaticEventListeners() {
     });
   }
 
+  // Sidebar view dropdown — trigger opens/closes, delegated item clicks switch view
+  var sidebarViewTrigger = $('sidebar-view-dropdown-trigger');
+  if (sidebarViewTrigger) on(sidebarViewTrigger, 'click', toggleSidebarViewDropdown);
+
+  var sidebarViewMenu = $('sidebar-view-dropdown-menu');
+  if (sidebarViewMenu) {
+    sidebarViewMenu.addEventListener('click', function(e) {
+      var item = e.target.closest('[data-view]');
+      if (item) {
+        switchView(item.dataset.view);
+        // Close sidebar dropdown after selection
+        sidebarViewMenu.classList.add('hidden');
+        if (sidebarViewTrigger) sidebarViewTrigger.setAttribute('aria-expanded', 'false');
+      }
+    });
+  }
+
   // Click-outside closes the dropdown
   document.addEventListener('click', function(e) {
     var dropdown = $('view-dropdown-menu');
@@ -3204,6 +3288,9 @@ if (typeof module !== 'undefined' && module.exports) {
     closeViewDropdown,
     showNewViewInput,
     switchView,
+    // Sidebar view dropdown
+    renderSidebarViewDropdown,
+    toggleSidebarViewDropdown,
     // Manage Views settings tab
     renderViewsSettingsTab,
     _saveViewsAndRerender,

muxplex/frontend/index.html

@@ -49,7 +49,13 @@
     <div class="view-body">
       <div id="session-sidebar" class="session-sidebar">
         <div class="sidebar-header">
-          <span class="sidebar-title">Sessions</span>
+          <div class="sidebar-view-dropdown" id="sidebar-view-dropdown">
+            <button id="sidebar-view-dropdown-trigger" class="sidebar-view-trigger" aria-haspopup="true" aria-expanded="false" aria-controls="sidebar-view-dropdown-menu">
+              <span id="sidebar-view-label">All Sessions</span>
+              <span class="view-dropdown__caret" aria-hidden="true">&#9662;</span>
+            </button>
+            <div id="sidebar-view-dropdown-menu" class="view-dropdown__menu hidden" role="menu" aria-label="Switch view"></div>
+          </div>
           <button id="sidebar-collapse-btn" class="sidebar-collapse-btn" aria-label="Collapse session list">&#8249;</button>
         </div>
         <div id="sidebar-list" class="sidebar-list"></div>

muxplex/frontend/style.css

@@ -487,6 +487,41 @@ body {
   color: var(--text-muted);
 }
 
+/* Sidebar view switcher dropdown */
+.sidebar-view-dropdown {
+  position: relative;
+  flex: 1;
+  min-width: 0;
+}
+
+.sidebar-view-trigger {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  background: transparent;
+  border: none;
+  color: var(--text-muted);
+  font-size: 13px;
+  font-family: var(--font-ui);
+  cursor: pointer;
+  padding: 2px 4px;
+  border-radius: 4px;
+  max-width: 100%;
+  overflow: hidden;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+}
+
+.sidebar-view-trigger:hover {
+  color: var(--accent);
+}
+
+#sidebar-view-dropdown-menu {
+  left: 0;
+  top: calc(100% + 2px);
+  min-width: 180px;
+}
+
 .sidebar-list {
   flex: 1;
   overflow-y: auto;

muxplex/tests/test_frontend_html.py

@@ -195,19 +195,16 @@ def test_html_reconnect_overlay_outside_view_body() -> None:
 
 
 def test_html_session_sidebar_structure() -> None:
-    """#session-sidebar must contain .sidebar-header (with .sidebar-title and #sidebar-collapse-btn) and #sidebar-list."""
+    """#session-sidebar must contain .sidebar-header (with #sidebar-view-dropdown and #sidebar-collapse-btn) and #sidebar-list."""
     soup = _SOUP
     sidebar = soup.find(id="session-sidebar")
     assert sidebar is not None, "Missing #session-sidebar"
     # .sidebar-header
     sidebar_header = sidebar.find(class_="sidebar-header")
     assert sidebar_header is not None, "Missing .sidebar-header inside #session-sidebar"
-    # .sidebar-title with text 'Sessions'
+    # #sidebar-view-dropdown (replaces old .sidebar-title)
-    sidebar_title = sidebar_header.find(class_="sidebar-title")
+    sidebar_dropdown = sidebar_header.find(id="sidebar-view-dropdown")
-    assert sidebar_title is not None, "Missing .sidebar-title inside .sidebar-header"
+    assert sidebar_dropdown is not None, "Missing #sidebar-view-dropdown inside .sidebar-header"
-    assert "Sessions" in sidebar_title.get_text(), (
-        f".sidebar-title text must contain 'Sessions', got: {sidebar_title.get_text()!r}"
-    )
     # #sidebar-collapse-btn
     collapse_btn = sidebar_header.find(id="sidebar-collapse-btn")
     assert collapse_btn is not None, (
@@ -1501,3 +1498,25 @@ def test_settings_has_views_panel() -> None:
     # Must contain the empty message element
     empty_msg = panel.find(id="views-settings-empty")
     assert empty_msg is not None, "Missing #views-settings-empty inside views panel"
+
+
+# ============================================================
+# Sidebar View Switcher (task-10)
+# ============================================================
+
+
+def test_sidebar_view_dropdown_exists() -> None:
+    """#sidebar-view-dropdown-trigger must exist in the sidebar header."""
+    soup = _SOUP
+    trigger = soup.find(id="sidebar-view-dropdown-trigger")
+    assert trigger is not None, "Missing #sidebar-view-dropdown-trigger"
+    assert trigger.name == "button", (
+        f"#sidebar-view-dropdown-trigger must be a <button>, got: {trigger.name}"
+    )
+
+
+def test_sidebar_view_dropdown_menu_exists() -> None:
+    """#sidebar-view-dropdown-menu must exist in the sidebar header."""
+    soup = _SOUP
+    menu = soup.find(id="sidebar-view-dropdown-menu")
+    assert menu is not None, "Missing #sidebar-view-dropdown-menu"