diff --git a/app/routers/auth.py b/app/routers/auth.py
index 3f09d1d..de9ffcd 100644
--- a/app/routers/auth.py
+++ b/app/routers/auth.py
@@ -55,6 +55,7 @@ body{background:#191919;color:#fff;font-family:-apple-system,BlinkMacSystemFont,
     <button class="tab active" onclick="switchTab('login')" id="tab-login">Login</button>
     <button class="tab" onclick="switchTab('register')" id="tab-register">Register</button>
   </div>
+  <div id="expired-msg" class="success" style="display:none">⚠️ Your session has expired. Please log in again.</div>
   <div id="error-msg" class="error"></div>
   <div id="success-msg" class="success"></div>
   <form id="login-form" onsubmit="handleLogin(event)">
@@ -76,6 +77,8 @@ body{background:#191919;color:#fff;font-family:-apple-system,BlinkMacSystemFont,
   </div>
 </div>
 <script>
+// Show session expired banner if ?expired=1 in URL
+(function(){if(location.search.includes('expired=1')){var el=document.getElementById('expired-msg');if(el)el.style.display='block';}})();
 let mode='login';
 function switchTab(t){mode=t;document.querySelectorAll('.tab').forEach(el=>el.classList.remove('active'));document.getElementById('tab-'+t).classList.add('active');document.getElementById('name-group').style.display=t==='register'?'block':'none';document.getElementById('submit-btn').textContent=t==='register'?'Register':'Login';document.getElementById('error-msg').style.display='none';document.getElementById('success-msg').style.display='none';var lbl=t==='register'?'Register':'Login';var e1=document.getElementById('gitea-btn-label');var e2=document.getElementById('github-btn-label');if(e1)e1.textContent=lbl;if(e2)e2.textContent=lbl;}
 function togglePassword(){var pw=document.getElementById('password');var btn=pw.parentElement.querySelector('.pw-toggle');if(pw.type==='password'){pw.type='text';btn.textContent='🙈';}else{pw.type='password';btn.textContent='👁';}}
diff --git a/app/routers/board.py b/app/routers/board.py
index 71f587a..4a08ad8 100644
--- a/app/routers/board.py
+++ b/app/routers/board.py
@@ -791,23 +791,29 @@ async def create_page(request: Request, title: str = Query(default=""),
     """Create a new Markdown page, optionally as a sub-page."""
     user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
     ws_key = project if project else (user.get("login", "Bruno") if user else "Bruno")
-    with get_conn() as conn:
-        # Compute next sort_order for this parent
-        next_order = 0
-        parent_val = parent_id if parent_id > 0 else None
-        row = conn.execute(
-            "SELECT COALESCE(MAX(sort_order), -1) + 1 FROM pages WHERE workspace=? AND parent_id IS ?",
-            (ws_key, parent_val),
-        ).fetchone()
-        if row:
-            next_order = row[0]
-        cur = conn.execute(
-            "INSERT INTO pages (workspace, title, parent_section, parent_id, sort_order) VALUES (?,?,?,?,?)",
-            (ws_key, title, section, parent_val, next_order),
-        )
-        conn.commit()
-        page_id = cur.lastrowid
-    return {"status": "ok", "id": page_id, "title": title, "workspace": ws_key, "parent_id": parent_id}
+    page_title = title.strip() if title else "Untitled"
+    try:
+        with get_conn() as conn:
+            # Compute next sort_order for this parent
+            next_order = 0
+            parent_val = parent_id if parent_id > 0 else None
+            row = conn.execute(
+                "SELECT COALESCE(MAX(sort_order), -1) + 1 FROM pages WHERE workspace=? AND parent_id IS ?",
+                (ws_key, parent_val),
+            ).fetchone()
+            if row:
+                next_order = row[0]
+            cur = conn.execute(
+                "INSERT INTO pages (workspace, title, parent_section, parent_id, sort_order) VALUES (?,?,?,?,?)",
+                (ws_key, page_title, section, parent_val, next_order),
+            )
+            conn.commit()
+            page_id = cur.lastrowid
+        return {"status": "ok", "id": page_id, "title": page_title, "workspace": ws_key, "parent_id": parent_id}
+    except Exception as e:
+        logger.error("create_page failed: %s", e)
+        from fastapi.responses import JSONResponse
+        return JSONResponse({"error": "Failed to create page", "detail": str(e)}, status_code=500)
 
 
 @router.get("/api/pages/{page_id}")
diff --git a/app/routers/dashboard.py b/app/routers/dashboard.py
index 9816483..98b4df6 100644
--- a/app/routers/dashboard.py
+++ b/app/routers/dashboard.py
@@ -27,7 +27,7 @@ def _get_user_or_redirect(request: Request):
                     return {"id": 1, "login": "admin", "full_name": "Admin", "is_admin": True}
         except Exception:
             pass
-        return RedirectResponse("/auth/login?provider=local", status_code=302)
+        return RedirectResponse("/auth/login?provider=local&expired=1", status_code=302)
     return user
 
 
@@ -1285,7 +1285,7 @@ async def workspaces_page(request: Request):
     sidebar = _sidebar_data(request, [], include_workspace=False)
     user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
     if not user:
-        return RedirectResponse("/auth/login?provider=local", status_code=302)
+        return RedirectResponse("/auth/login?provider=local&expired=1", status_code=302)
     ctx = {**sidebar, "user": user}
     # Pass active workspace for breadcrumb nav menu (null on workspaces home)
     ws = _get_active_workspace(request, user_id=_get_user_id(request))
diff --git a/app/templates/base.html b/app/templates/base.html
index 779c5cd..7e7e61a 100644
--- a/app/templates/base.html
+++ b/app/templates/base.html
@@ -6,6 +6,89 @@
   <title>FlowDeck — {% block title_prefix %}Home{% endblock %}</title>
   <link rel="icon" type="image/svg+xml" href="/static/favicon.svg">
   <link rel="stylesheet" href="/static/css/app.css?v=3.0.0">
+  <style>
+    /* ── Mobile responsive (v4.0.2) ── */
+    @media (max-width: 768px) {
+      .sidebar {
+        position: fixed;
+        left: 0;
+        top: 0;
+        bottom: 0;
+        z-index: 100;
+        width: 280px;
+        transform: translateX(-100%);
+        transition: transform .2s ease;
+      }
+      .sidebar.mobile-open {
+        transform: translateX(0);
+        box-shadow: 4px 0 24px rgba(0,0,0,.5);
+      }
+      .sidebar-overlay.visible {
+        position: fixed;
+        inset: 0;
+        background: rgba(0,0,0,.5);
+        z-index: 99;
+      }
+      .main-wrapper {
+        margin-left: 0 !important;
+        width: 100%;
+      }
+      .unified-header {
+        padding: 8px 12px;
+      }
+      .page-editor-wrapper {
+        padding: 16px 8px;
+      }
+      .page-title-block {
+        padding: 16px 8px;
+      }
+      .blocks-container {
+        padding: 0 4px;
+      }
+      .share-dialog, .more-menu, .activity-popover {
+        position: fixed !important;
+        top: 50% !important;
+        left: 50% !important;
+        transform: translate(-50%, -50%) !important;
+        width: 92vw;
+        max-width: 400px;
+        max-height: 80vh;
+        overflow-y: auto;
+      }
+      .landing-nav {
+        padding: 12px 16px;
+      }
+      .hero {
+        padding: 40px 16px 30px;
+      }
+      .hero h1 {
+        font-size: 1.8rem;
+      }
+      .features {
+        grid-template-columns: 1fr;
+        padding: 0 16px 30px;
+      }
+      .library-card-grid {
+        grid-template-columns: 1fr;
+      }
+      .view-tabs {
+        overflow-x: auto;
+        flex-wrap: nowrap;
+      }
+    }
+    @media (max-width: 480px) {
+      .hero h1 {
+        font-size: 1.5rem;
+      }
+      .hero p {
+        font-size: 15px;
+      }
+      .btn {
+        padding: 8px 16px;
+        font-size: 13px;
+      }
+    }
+  </style>
   <script src="/static/js/htmx.min.js"></script>
   <script src="/static/js/alpine.min.js" defer></script>
   <script src="/static/js/sortable.min.js" defer></script>
diff --git a/tests/test_app.py b/tests/test_app.py
index 547596a..0a2e3a1 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -1914,3 +1914,92 @@ def test_page_renders_breadcrumb_data(client):
     assert 'id="fd-breadcrumb-data"' in resp.text
     assert '"Home"' in resp.text
     assert "fdBreadcrumb" in resp.text
+
+
+# ═══════════ v4.0.2 — Regression tests (critical paths) ═══════════
+
+
+def test_landing_page_no_auth(client):
+    """Visiting / without auth shows the landing page."""
+    resp = client.get("/", follow_redirects=False)
+    assert resp.status_code == 200
+    assert "FlowDeck" in resp.text
+    assert "Get started free" in resp.text or "Get started" in resp.text
+
+
+def test_register_page_get(client):
+    """GET /auth/register shows the registration form."""
+    resp = client.get("/auth/register", follow_redirects=False)
+    assert resp.status_code == 200
+    assert "register" in resp.text.lower()
+
+
+def test_login_page_shows_expired_banner(client):
+    """Login page with ?expired=1 shows session expired message."""
+    resp = client.get("/auth/login?provider=local&expired=1", follow_redirects=False)
+    assert resp.status_code == 200
+    assert "expired" in resp.text.lower()
+
+
+def test_create_page_defaults_to_untitled(client):
+    """Creating a page with empty title defaults to 'Untitled'."""
+    resp = client.post("/board/api/pages?title=&section=Private", follow_redirects=False)
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["title"] == "Untitled"
+
+
+def test_styled_404_page(client):
+    """Unknown routes return a styled 404 HTML page."""
+    resp = client.get("/this-does-not-exist-xyz", follow_redirects=False)
+    assert resp.status_code == 404
+    assert "404" in resp.text
+    assert "FlowDeck" in resp.text
+
+
+def test_api_404_returns_json(client):
+    """Unknown API routes return JSON, not HTML."""
+    resp = client.get("/api/does-not-exist", follow_redirects=False)
+    assert resp.status_code == 404
+    data = resp.json()
+    assert "detail" in data
+
+
+def test_login_validation_empty_fields(client):
+    """Login with empty fields returns 400 error."""
+    resp = client.post("/auth/local-login", json={"email": "", "password": ""})
+    assert resp.status_code == 400
+    data = resp.json()
+    assert "error" in data
+
+
+def test_register_validation_short_password(client):
+    """Registration with short password returns 400."""
+    resp = client.post("/auth/register", json={
+        "email": "test@test.com", "password": "ab", "name": "Test"
+    })
+    assert resp.status_code == 400
+
+
+def test_register_duplicate_rejected(client):
+    """Duplicate registration returns 409."""
+    # Register first time
+    r1 = client.post("/auth/register", json={
+        "email": "duptest2", "password": "password123", "name": "Dup"
+    })
+    assert r1.status_code == 200
+    # Second registration with same email should fail
+    r2 = client.post("/auth/register", json={
+        "email": "duptest2", "password": "password123", "name": "Dup2"
+    })
+    assert r2.status_code == 409
+    assert "already exists" in r2.json().get("error", "").lower()
+
+
+def test_session_expired_redirect(client):
+    """Unauthenticated access to protected page redirects with expired param."""
+    resp = client.get("/workspaces", follow_redirects=False)
+    assert resp.status_code == 302
+    location = resp.headers.get("location", "")
+    assert "login" in location
+    assert "expired=1" in location