diff --git a/app.py b/app.py
index db1c926..e03669a 100644
--- a/app.py
+++ b/app.py
@@ -2392,6 +2392,14 @@ def is_valid_local(url):
             if any(b in user_agent for b in ['Mozilla', 'Chrome', 'Safari', 'Edge']):
                 abort(403)
 
+    # 3. Master Auth Validation
+    if request.path.startswith("/api/") and request.path != "/api/master/status":
+        locks = load_locks()
+        if "__master__" in locks:
+            master_pass = request.headers.get("X-Master-Password", "")
+            if not check_lock("__master__", master_pass):
+                return jsonify({"error": "Master locked", "master_locked": True}), 401
+
 # ─── Routes ───────────────────────────────────────────────────────
 
 
@@ -2400,6 +2408,13 @@ def index():
     return send_from_directory("ui", "index.html")
 
 
+@app.route("/api/master/status")
+def master_status():
+    locks = load_locks()
+    is_locked = "__master__" in locks
+    return jsonify({"locked": is_locked})
+
+
 @app.route("/api/scripts")
 def list_scripts():
     return jsonify(get_all_scripts())
diff --git a/ui/app.js b/ui/app.js
index a4b7f5a..a27ddfc 100644
--- a/ui/app.js
+++ b/ui/app.js
@@ -25,6 +25,7 @@ const API = {
     reliability_trends: '/api/reliability/trends',
     reliability_recommendations: '/api/reliability/recommendations',
     reliability_diagnostics: '/api/reliability/diagnostics',
+    master_status: '/api/master/status',
 };
 
 // ─── State ────────────────────────────────────────────────
@@ -39,6 +40,7 @@ let state = {
     cmdHistoryIndex: -1,
     historyQuery: '',
     historyFilter: 'all',
+    masterPassword: null,
     historyEntries: [],
     historySummary: {
         total: 0,
@@ -137,6 +139,70 @@ function getCategoryIcon(name) {
     return ICONS[name.toLowerCase()] || ICONS.default;
 }
 
+// ─── Global Fetch Wrapper ──────────────────────────────────────────
+const originalFetch = window.fetch;
+window.fetch = async function(...args) {
+    let [resource, config] = args;
+    config = config || {};
+    
+    if (typeof resource === 'string' && resource.startsWith('/api/') && state.masterPassword) {
+        config.headers = config.headers || {};
+        config.headers['X-Master-Password'] = state.masterPassword;
+    }
+    
+    let res = await originalFetch(resource, config);
+    
+    if (res.status === 401) {
+        try {
+            const clone = res.clone();
+            const data = await clone.json();
+            if (data.master_locked) {
+                return new Promise((resolve, reject) => {
+                    const modal = document.getElementById('master-auth-modal');
+                    const input = document.getElementById('master-auth-password');
+                    const submit = document.getElementById('master-auth-submit');
+                    
+                    if (!modal) return resolve(res);
+                    
+                    modal.classList.add('active');
+                    input.value = '';
+                    input.focus();
+                    
+                    const cleanup = () => {
+                        submit.removeEventListener('click', onSubmit);
+                        input.removeEventListener('keydown', onKey);
+                    };
+
+                    const onSubmit = async () => {
+                        const pwd = input.value;
+                        if (!pwd) return;
+                        
+                        state.masterPassword = pwd;
+                        modal.classList.remove('active');
+                        cleanup();
+                        
+                        try {
+                            const retryRes = await window.fetch(resource, config);
+                            resolve(retryRes);
+                        } catch (e) {
+                            reject(e);
+                        }
+                    };
+                    
+                    const onKey = (e) => { if (e.key === 'Enter') onSubmit(); };
+                    
+                    submit.addEventListener('click', onSubmit);
+                    input.addEventListener('keydown', onKey);
+                });
+            }
+        } catch (e) {
+            console.error(e);
+        }
+    }
+    
+    return res;
+};
+
 // Register global lifecycle cleanup listeners exactly once
 if (!window.__devshell_lifecycle_registered) {
     window.__devshell_lifecycle_registered = true;
@@ -3660,6 +3726,7 @@ function bindEvents() {
 
     // Lock Features
     const btnLock = document.getElementById('btn-lock');
+    const btnMasterLock = document.getElementById('btn-master-lock');
     const lockOverlay = document.getElementById('lock-modal-overlay');
 
     function openLockModal(targetPath, isLocked) {
@@ -3689,8 +3756,7 @@ function bindEvents() {
     if (btnLock && lockOverlay) {
         btnLock.addEventListener('click', () => {
             if (!state.activeScript) return;
-
-            // Check if it's already locked from state
+            
             let isLocked = false;
             for (let cat in state.scripts) {
                 let sc = state.scripts[cat].find(s => s.relative_path === state.activeScript);
diff --git a/ui/index.html b/ui/index.html
index 66e5a01..c7e4156 100644
--- a/ui/index.html
+++ b/ui/index.html
@@ -46,6 +46,9 @@ <h1>Dev<span class="accent">Shell</span></h1>
         </div>
         <div class="header-right">
       <div class="header-right">
+            <button class="btn-icon" id="btn-master-lock" title="Global Master Lock" aria-label="Toggle Global Master Lock" style="margin-right: 4px; display: flex; align-items: center; justify-content: center;">
+                <svg xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z"/></svg>
+            </button>
             <button class="btn-icon" id="theme-toggle-btn" title="Toggle Light/Dark Mode" aria-label="Toggle UI Theme" style="margin-right: 4px; display: flex; align-items: center; justify-content: center;">
                 <svg id="theme-icon-moon" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 3a6 6 0 0 0 9 9 9 9 0 1 1-9-9Z"/></svg>
                 <svg id="theme-icon-sun" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" style="display: none;"><circle cx="12" cy="12" r="4"/><path d="M12 2v2"/><path d="M12 20v2"/><path d="m4.93 4.93 1.41 1.41"/><path d="m18.36 18.36 1.41 1.41"/><path d="M20 12h2"/><path d="M2 12h2"/><path d="m6.34 17.66-1.41 1.41"/><path d="m19.07 4.93-1.41 1.41"/></svg>
@@ -1057,7 +1060,24 @@ <h2>Workspace Profiles</h2>
             </div>
         </div>
     </div>
-
+    <!-- Master Auth Modal -->
+    <div id="master-auth-modal" class="modal-overlay">
+        <div class="modal">
+            <div class="modal-header">
+                <h2>Master Authentication</h2>
+            </div>
+            <div class="modal-body">
+                <p>The application is locked. Please enter the master password to continue.</p>
+                <div class="form-group" style="margin-top: 15px;">
+                    <label>Master Password</label>
+                    <input type="password" id="master-auth-password" class="w-full">
+                </div>
+                <div style="margin-top: 20px; display: flex; justify-content: flex-end;">
+                    <button id="master-auth-submit" class="btn">Unlock</button>
+                </div>
+            </div>
+        </div>
+    </div>
 </body>
 
 </html>
\ No newline at end of file