diff --git a/frontend/src/app/components/Layout/AppShell.tsx b/frontend/src/app/components/Layout/AppShell.tsx
index 753cba04..64b13179 100644
--- a/frontend/src/app/components/Layout/AppShell.tsx
+++ b/frontend/src/app/components/Layout/AppShell.tsx
@@ -444,7 +444,9 @@ const AppShell: React.FC = () => {
       {/* Sidebar retired: dashboards switch via the macOS-Spaces top strip; a slim band below the
           spaces hot zone keeps the frameless window draggable (the sidebar's drag strip is gone). */}
       {isDashboardViewActive && !v3FlowActive && <SpacesStrip />}
-      <Box sx={{ position: 'fixed', top: 3, left: 260, right: 0, height: 22, zIndex: 5, WebkitAppRegion: 'drag' }} />
+      {/* Tagged so tiling can inset below it: this strip is a window-DRAG region, so anything tiled
+          underneath it loses those pixels to dragging the OS window instead of taking clicks. */}
+      <Box data-top-chrome sx={{ position: 'fixed', top: 3, left: 260, right: 0, height: 22, zIndex: 5, WebkitAppRegion: 'drag' }} />
       {/* Top bar dropped (Arc/Zen): a zero-height anchor left only to float the agent-activity island at top-center; the island renders nothing when idle. */}
       <Box
         sx={{
diff --git a/frontend/src/app/pages/Dashboard/canvas/tiledGeometry.ts b/frontend/src/app/pages/Dashboard/canvas/tiledGeometry.ts
index 0cd67c39..bc498bc3 100644
--- a/frontend/src/app/pages/Dashboard/canvas/tiledGeometry.ts
+++ b/frontend/src/app/pages/Dashboard/canvas/tiledGeometry.ts
@@ -40,6 +40,10 @@ export interface ZoneRect {
 interface Workspace {
   x0: number;
   x1: number;
+  // Top chrome (the frameless window's drag strip) overlays the canvas, so a tile placed at y=GAP
+  // sits UNDER it: the margin exists but is invisible, and worse, those pixels drag the OS window
+  // instead of reaching the app. Only left and right were ever inset, which is the missing-top-gap bug.
+  y0: number;
   w: number;
   h: number;
 }
@@ -47,7 +51,7 @@ interface Workspace {
 // Pure layout, never the camera, so a pan/zoom frame reads nothing back out of the DOM.
 let workspace: Workspace | null = null;
 
-const CHROME_SELECTORS = ['[data-canvas-viewport]', '[data-desktop-dock]', '[data-minimized-rail]'];
+const CHROME_SELECTORS = ['[data-canvas-viewport]', '[data-desktop-dock]', '[data-minimized-rail]', '[data-top-chrome]'];
 
 // How much of one edge a chrome strip claims. It only counts when it is real, overlaps the viewport,
 // and actually hugs the edge it claims, so an absent or collapsed strip yields 0, never a bogus inset.
@@ -60,14 +64,28 @@ function edgeInset(selector: string, vp: DOMRect, side: 'left' | 'right'): numbe
   return r.left < vp.right && r.right > vp.left + vp.width * 0.75 ? vp.right - r.left + GAP : 0;
 }
 
+// How far down the top chrome reaches into the viewport. Same shape as edgeInset: absent or
+// non-overlapping chrome yields 0, never a bogus inset.
+function topInset(vp: DOMRect): number {
+  let deepest = 0;
+  document.querySelectorAll('[data-top-chrome]').forEach((el) => {
+    const r = el.getBoundingClientRect();
+    if (!(r.height > 0) || r.bottom <= vp.top) return;
+    if (r.top > vp.top + vp.height * 0.25) return;
+    deepest = Math.max(deepest, r.bottom - vp.top);
+  });
+  return deepest;
+}
+
 function measureWorkspace(): Workspace {
   const el = document.querySelector('[data-canvas-viewport]');
   const r = el?.getBoundingClientRect();
-  if (!r || !(r.width > 0 && r.height > 0)) return { x0: 0, x1: 0, w: window.innerWidth, h: window.innerHeight };
+  if (!r || !(r.width > 0 && r.height > 0)) return { x0: 0, x1: 0, y0: 0, w: window.innerWidth, h: window.innerHeight };
   // macOS model: a tiled window sits BESIDE the Dock and beside the minimized rail, never under either.
   return {
     x0: edgeInset('[data-desktop-dock]', r, 'left'),
     x1: edgeInset('[data-minimized-rail]', r, 'right'),
+    y0: topInset(r),
     w: r.width,
     h: r.height,
   };
@@ -77,16 +95,17 @@ function measureWorkspace(): Workspace {
 export function zoneRect(zone: string): ZoneRect | null {
   const ws = workspace ?? (workspace = measureWorkspace());
   const usableW = ws.w - ws.x0 - ws.x1;
+  const usableH = ws.h - ws.y0;
   if (zone === 'fullscreen') {
-    return { x: ws.x0 + GAP, y: GAP, w: usableW - GAP * 2, h: ws.h - GAP * 2 };
+    return { x: ws.x0 + GAP, y: ws.y0 + GAP, w: usableW - GAP * 2, h: usableH - GAP * 2 };
   }
   const z = TILE_ZONES[zone];
   if (!z) return null;
   return {
     x: ws.x0 + z.x * usableW + GAP,
-    y: z.y * ws.h + GAP,
+    y: ws.y0 + z.y * usableH + GAP,
     w: z.w * usableW - GAP * 2,
-    h: z.h * ws.h - GAP * 2,
+    h: z.h * usableH - GAP * 2,
   };
 }