refactor: rewrite sidebar functions to use server-side settings

- Remove SIDEBAR_KEY constant (was an undefined variable bug)
- Rewrite initSidebar() to read sidebarOpen from _serverSettings
- Rewrite toggleSidebar() to derive state from DOM class and persist
  to server via patchServerSetting
- Rewrite bindSidebarClickAway() to persist collapsed state via
  patchServerSetting instead of localStorage
- Add 7 tests verifying SIDEBAR_KEY removal and _serverSettings usage

muxplex/frontend/app.js

@@ -598,24 +598,24 @@ const SIDEBAR_NARROW_THRESHOLD = 960;
 
 /**
  * Initialise sidebar open/closed state on page load.
- * Reads muxplex.sidebarOpen from localStorage (JSON.parse with try/catch).
+ * Reads sidebarOpen from _serverSettings cache.
  * Defaults to open on wide screens (innerWidth >= 960) when no stored value.
  * Applies sidebar--collapsed class accordingly and persists the initial state.
  */
 function initSidebar() {
-  let isOpen;
-  try {
-    const stored = localStorage.getItem(SIDEBAR_KEY);
-    if (stored !== null) {
-      isOpen = JSON.parse(stored);
+  var stored = _serverSettings ? _serverSettings.sidebarOpen : null;
+  var isOpen;
+
+  if (stored !== null && stored !== undefined) {
+    isOpen = !!stored;
   } else {
     isOpen = window.innerWidth >= SIDEBAR_NARROW_THRESHOLD;
-    }
-  } catch (_) {
-    isOpen = window.innerWidth >= SIDEBAR_NARROW_THRESHOLD;
+    // Persist the auto-detected value (fire-and-forget)
+    if (_serverSettings) _serverSettings.sidebarOpen = isOpen;
+    patchServerSetting('sidebarOpen', isOpen);
   }
 
-  const sidebar = $('session-sidebar');
+  var sidebar = $('session-sidebar');
   if (sidebar) {
     if (isOpen) {
       sidebar.classList.remove('sidebar--collapsed');
@@ -623,51 +623,32 @@ function initSidebar() {
       sidebar.classList.add('sidebar--collapsed');
     }
   }
-
-  // Persist initial state
-  try {
-    localStorage.setItem(SIDEBAR_KEY, JSON.stringify(isOpen));
-  } catch (_) { /* blocked — ok */ }
 }
 
 /**
  * Toggle the sidebar open/closed state.
- * Reads current state from localStorage, inverts it, persists, applies
- * sidebar--collapsed class, and updates the collapse button text.
+ * Derives current state from DOM class, inverts it, persists to server,
+ * applies sidebar--collapsed class, and updates the collapse button text.
  * Button shows ‹ when open, › when closed.
  */
 function toggleSidebar() {
-  let isOpen;
-  try {
-    const stored = localStorage.getItem(SIDEBAR_KEY);
-    isOpen = stored !== null ? JSON.parse(stored) : true;
-  } catch (_) {
-    isOpen = true;
-  }
+  var sidebar = $('session-sidebar');
+  if (!sidebar) return;
 
-  // Invert state
+  var isOpen = !sidebar.classList.contains('sidebar--collapsed');
   isOpen = !isOpen;
 
-  // Persist
-  try {
-    localStorage.setItem(SIDEBAR_KEY, JSON.stringify(isOpen));
-  } catch (_) { /* blocked — ok */ }
-
-  // Apply class
-  const sidebar = $('session-sidebar');
-  if (sidebar) {
   if (isOpen) {
     sidebar.classList.remove('sidebar--collapsed');
   } else {
     sidebar.classList.add('sidebar--collapsed');
   }
-  }
 
-  // Update collapse button text (‹ when open, › when closed)
-  const collapseBtn = $('sidebar-collapse-btn');
-  if (collapseBtn) {
-    collapseBtn.textContent = isOpen ? '\u2039' : '\u203a';
-  }
+  if (_serverSettings) _serverSettings.sidebarOpen = isOpen;
+  patchServerSetting('sidebarOpen', isOpen);
+
+  var collapseBtn = $('sidebar-collapse-btn');
+  if (collapseBtn) collapseBtn.textContent = isOpen ? '\u2039' : '\u203a';
 }
 
 /**
@@ -679,17 +660,16 @@ function toggleSidebar() {
  *   - the sidebar is already collapsed
  */
 function bindSidebarClickAway() {
-  const container = $('terminal-container');
+  var container = $('terminal-container');
   if (!container) return;
-  container.addEventListener('click', () => {
+  container.addEventListener('click', function() {
     if (window.innerWidth >= SIDEBAR_NARROW_THRESHOLD) return;
-    const sidebar = $('session-sidebar');
+    var sidebar = $('session-sidebar');
     if (!sidebar) return;
     if (sidebar.classList.contains('sidebar--collapsed')) return;
     sidebar.classList.add('sidebar--collapsed');
-    try {
-      localStorage.setItem(SIDEBAR_KEY, JSON.stringify(false));
-    } catch (_) { /* blocked — ok */ }
+    if (_serverSettings) _serverSettings.sidebarOpen = false;
+    patchServerSetting('sidebarOpen', false);
   });
 }
 

muxplex/tests/test_frontend_js.py

@@ -344,7 +344,9 @@ def test_get_display_settings_reads_server_settings() -> None:
     )
     assert match, "getDisplaySettings function not found"
     body = match.group(1)
-    assert "_serverSettings" in body, "getDisplaySettings must read from _serverSettings"
+    assert "_serverSettings" in body, (
+        "getDisplaySettings must read from _serverSettings"
+    )
     assert "localStorage" not in body, (
         "getDisplaySettings must not use localStorage — display settings are server-side"
     )
@@ -429,7 +431,9 @@ def test_get_display_settings_reads_from_server_settings() -> None:
     )
     assert match, "getDisplaySettings function not found"
     body = match.group(1)
-    assert "_serverSettings" in body, "getDisplaySettings must read from _serverSettings"
+    assert "_serverSettings" in body, (
+        "getDisplaySettings must read from _serverSettings"
+    )
     assert "localStorage" not in body, (
         "getDisplaySettings must not use localStorage — display settings are server-side"
     )
@@ -492,9 +496,7 @@ def test_on_display_setting_change_catches_errors() -> None:
     )
     assert match, "onDisplaySettingChange function not found"
     body = match.group(1)
-    assert ".catch" in body, (
-        "onDisplaySettingChange must handle errors via .catch()"
-    )
+    assert ".catch" in body, "onDisplaySettingChange must handle errors via .catch()"
 
 
 # ── openSettings implementation ───────────────────────────────────────────────
@@ -2597,3 +2599,107 @@ def test_open_session_bell_clear_is_fire_and_forget() -> None:
         assert "await" not in line, (
             f"openSession bell-clear POST must NOT be awaited (fire-and-forget): {line.strip()}"
         )
+
+
+# ─── Task 4: sidebar functions use server-side settings ──────────────────────
+
+
+def test_no_sidebar_key_constant() -> None:
+    """SIDEBAR_KEY constant must be removed — sidebar state moves to _serverSettings."""
+    assert "SIDEBAR_KEY" not in _JS, (
+        "SIDEBAR_KEY constant must be removed from app.js; "
+        "sidebar open/closed state is now stored in _serverSettings.sidebarOpen"
+    )
+
+
+def test_init_sidebar_reads_server_settings() -> None:
+    """initSidebar must read sidebarOpen from _serverSettings, not localStorage."""
+    match = re.search(
+        r"function initSidebar\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "initSidebar function not found"
+    body = match.group(1)
+    assert "_serverSettings" in body, (
+        "initSidebar must read sidebarOpen from _serverSettings"
+    )
+    assert "localStorage" not in body, (
+        "initSidebar must not use localStorage — sidebar state is now server-side"
+    )
+
+
+def test_init_sidebar_calls_patch_server_setting() -> None:
+    """initSidebar must call patchServerSetting to persist the auto-detected state."""
+    match = re.search(
+        r"function initSidebar\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "initSidebar function not found"
+    body = match.group(1)
+    assert "patchServerSetting" in body, (
+        "initSidebar must call patchServerSetting to persist the auto-detected sidebar state"
+    )
+
+
+def test_toggle_sidebar_reads_server_settings() -> None:
+    """toggleSidebar must derive state from the DOM class, not from localStorage."""
+    match = re.search(
+        r"function toggleSidebar\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "toggleSidebar function not found"
+    body = match.group(1)
+    assert "_serverSettings" in body, (
+        "toggleSidebar must write new state to _serverSettings"
+    )
+    assert "localStorage" not in body, (
+        "toggleSidebar must not use localStorage — sidebar state is now server-side"
+    )
+
+
+def test_toggle_sidebar_calls_patch_server_setting() -> None:
+    """toggleSidebar must call patchServerSetting to persist the toggled state."""
+    match = re.search(
+        r"function toggleSidebar\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "toggleSidebar function not found"
+    body = match.group(1)
+    assert "patchServerSetting" in body, (
+        "toggleSidebar must call patchServerSetting to persist the toggled sidebar state"
+    )
+
+
+def test_bind_sidebar_click_away_uses_server_settings() -> None:
+    """bindSidebarClickAway must write false to _serverSettings on collapse."""
+    match = re.search(
+        r"function bindSidebarClickAway\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "bindSidebarClickAway function not found"
+    body = match.group(1)
+    assert "_serverSettings" in body, (
+        "bindSidebarClickAway must write false to _serverSettings.sidebarOpen on collapse"
+    )
+    assert "localStorage" not in body, (
+        "bindSidebarClickAway must not use localStorage — sidebar state is now server-side"
+    )
+
+
+def test_bind_sidebar_click_away_calls_patch_server_setting() -> None:
+    """bindSidebarClickAway must call patchServerSetting to persist collapsed state."""
+    match = re.search(
+        r"function bindSidebarClickAway\s*\(\s*\)\s*\{(.*?)(?=\nfunction |\n// ─|\n/\*\*)",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "bindSidebarClickAway function not found"
+    body = match.group(1)
+    assert "patchServerSetting" in body, (
+        "bindSidebarClickAway must call patchServerSetting to persist collapsed state"
+    )