diff --git a/packages/dashboard/app/__tests__/footer-safe-layout.test.ts b/packages/dashboard/app/__tests__/footer-safe-layout.test.ts
index c4a107d2cc..cf82186a97 100644
--- a/packages/dashboard/app/__tests__/footer-safe-layout.test.ts
+++ b/packages/dashboard/app/__tests__/footer-safe-layout.test.ts
@@ -56,11 +56,25 @@ describe("footer-safe project workspace layout", () => {
   // ── .project-content--with-footer (desktop) ────────────────────────
 
   describe(".project-content--with-footer desktop", () => {
-    const footerBlock = loadAllAppCssBaseOnly().match(
-      /\.project-content--with-footer\s*\{[^}]*\}/,
-    )?.[0];
+    /*
+    FNXC:ViewportChrome 2026-08-03-00:13:
+    Match the unscoped base rule only. Mode-scoped overrides
+    (`html[data-viewport-mode=…] .project-content--with-footer`) also contain the
+    class name and would otherwise win a first-match scan. Require both the 36px
+    token and padding-bottom so token-only mode overrides cannot satisfy this contract.
+    */
+    const baseCss = loadAllAppCssBaseOnly();
+    const footerBlock = [...baseCss.matchAll(/\.project-content--with-footer\s*\{[^}]*\}/g)]
+      .map((match) => match[0])
+      .find(
+        (block) =>
+          block.includes("--executor-footer-height: 36px") &&
+          block.includes("padding-bottom: var(--executor-footer-height)") &&
+          !block.includes("data-viewport-mode"),
+      );
 
     it("defines --executor-footer-height token as 36px", () => {
+      expect(footerBlock).toBeTruthy();
       expect(footerBlock).toContain("--executor-footer-height: 36px");
     });
 
diff --git a/packages/dashboard/app/__tests__/viewport-chrome-mode-alignment.test.ts b/packages/dashboard/app/__tests__/viewport-chrome-mode-alignment.test.ts
new file mode 100644
index 0000000000..9e21ffec25
--- /dev/null
+++ b/packages/dashboard/app/__tests__/viewport-chrome-mode-alignment.test.ts
@@ -0,0 +1,72 @@
+import { describe, expect, it } from "vitest";
+import { loadAllAppCss } from "../test/cssFixture";
+
+/**
+ * Viewport chrome alignment (tablet-class narrow widths).
+ *
+ * Surface enumeration:
+ * - Left sidebar visibility (LeftSidebarNav.css)
+ * - Mobile bottom tab bar visibility (MobileNavBar.css)
+ * - Executor footer bottom stacking above mobile nav (ExecutorStatusBar.css)
+ * - Footer height token on project-content (ProjectSelector.css + ExecutorStatusBar.css)
+ * - Right dock hide/show (RightDock.css)
+ * - data-viewport-mode publisher (useViewportMode.ts)
+ *
+ * Original symptom: mid-tablet / tablet-class ≤768 CSS px showed no left sidebar,
+ * no bottom tab bar, and a floating footer overlapping board content with empty
+ * space below (CSS elevated the footer for a mobile nav that JS never mounted).
+ *
+ * Assertion: shell chrome CSS keys display and footer stacking off
+ * `html[data-viewport-mode="…"]` so tablet/desktop keep left sidebar + footer at
+ * the true bottom even when the CSS width is still ≤768.
+ */
+
+const css = loadAllAppCss();
+
+describe("viewport chrome mode alignment", () => {
+  it("publishes mode-driven left sidebar show/hide that overrides the width-only hide", () => {
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.left-sidebar-nav\s*\{[^}]*display:\s*flex/,
+    );
+    expect(css).toMatch(/html\[data-viewport-mode="mobile"\]\s*\.left-sidebar-nav\s*\{[^}]*display:\s*none/);
+    // Width fallback remains for no-JS / first paint on true phones.
+    expect(css).toMatch(/@media\s*\(\s*max-width:\s*768px\s*\)\s*\{[\s\S]*?\.left-sidebar-nav\s*\{[^}]*display:\s*none/);
+  });
+
+  it("publishes mode-driven mobile nav show/hide so tablet never reserves a phantom tab bar", () => {
+    expect(css).toMatch(/html\[data-viewport-mode="mobile"\]\s*\.mobile-nav-bar\s*\{[^}]*display:\s*flex/);
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.mobile-nav-bar\s*\{[^}]*display:\s*none/,
+    );
+  });
+
+  it("pins the executor footer to the true bottom on tablet/desktop mode", () => {
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.executor-status-bar\s*\{[^}]*bottom:\s*var\(--icb-bottom-offset,\s*0px\)/,
+    );
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.executor-status-bar\s*\{[^}]*height:\s*36px/,
+    );
+    // Mobile mode still elevates above the tab bar.
+    expect(css).toMatch(
+      /html\[data-viewport-mode="mobile"\]\s*\.executor-status-bar\s*\{[\s\S]*?bottom:\s*calc\([^)]*var\(--mobile-nav-height\)/,
+    );
+  });
+
+  it("keeps the desktop footer-height token for tablet/desktop mode after mobile overrides", () => {
+    // May share a declaration block with .dashboard-project-shell (comma selector).
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.project-content--with-footer[\s\S]{0,180}?\{[^}]*--executor-footer-height:\s*36px/,
+    );
+    expect(css).toMatch(
+      /html\[data-viewport-mode="mobile"\]\s*\.project-content--with-footer\s*\{[^}]*--executor-footer-height:\s*calc\(var\(--space-lg\)\s*\*\s*2\s*\+\s*var\(--space-xs\)\)/,
+    );
+  });
+
+  it("aligns right-dock mobile hide with viewport mode", () => {
+    expect(css).toMatch(/html\[data-viewport-mode="mobile"\]\s*\.right-dock\s*\{[^}]*display:\s*none/);
+    expect(css).toMatch(
+      /html:is\(\[data-viewport-mode="tablet"\],\s*\[data-viewport-mode="desktop"\]\)\s*\.right-dock\s*\{[^}]*display:\s*flex/,
+    );
+  });
+});
diff --git a/packages/dashboard/app/components/ExecutorStatusBar.css b/packages/dashboard/app/components/ExecutorStatusBar.css
index 5be63cc167..d0dab310f8 100644
--- a/packages/dashboard/app/components/ExecutorStatusBar.css
+++ b/packages/dashboard/app/components/ExecutorStatusBar.css
@@ -417,6 +417,10 @@ FN-6887 makes the footer status bar the canonical desktop/tablet terminal launch
 }
 
 /* Responsive: collapse on small screens */
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+Elevating the fixed footer above `--mobile-nav-height` is only correct when the mobile tab bar is actually mounted (JS mode=mobile). Tablet-class devices in the ≤768 CSS px band stay mode=tablet with a left sidebar and no bottom tab bar; the width-only rule left a dead band under the footer and made it paint over board content. Keep width media as a no-JS fallback for true phones, then reassert desktop bottom/height when mode is tablet or desktop.
+*/
 @media (max-width: 768px) {
   /*
   FNXC:MobileFooter 2026-06-23-22:10:
@@ -465,6 +469,45 @@ FN-6887 makes the footer status bar the canonical desktop/tablet terminal launch
 
 }
 
+html[data-viewport-mode="mobile"] .project-content--with-footer {
+  --executor-footer-height: calc(var(--space-lg) * 2 + var(--space-xs));
+}
+
+html[data-viewport-mode="mobile"] .executor-status-bar {
+  padding: var(--space-xs) var(--space-md);
+  gap: 4px;
+  font-size: 11px;
+  height: calc(var(--space-lg) * 2 + var(--space-xs));
+  overflow: hidden;
+  bottom: calc(var(--icb-bottom-offset, 0px) + var(--mobile-nav-height) + max(env(safe-area-inset-bottom, 0px), 12px) + var(--standalone-bottom-gap));
+}
+
+html[data-viewport-mode="mobile"] .executor-status-bar.executor-status-bar--keyboard-open {
+  bottom: 0;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .project-content--with-footer,
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .dashboard-project-shell {
+  --executor-footer-height: 36px;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .executor-status-bar {
+  bottom: var(--icb-bottom-offset, 0px);
+  height: 36px;
+  padding: var(--space-xs) var(--space-lg);
+  gap: var(--space-sm);
+  font-size: 12px;
+  overflow: visible;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .executor-status-bar__segment--time {
+  display: flex;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .executor-status-bar.executor-status-bar--keyboard-open {
+  bottom: var(--icb-bottom-offset, 0px);
+}
+
 /* Light theme support */
 [data-theme="light"] .executor-status-bar {
   background: var(--surface);
diff --git a/packages/dashboard/app/components/LeftSidebarNav.css b/packages/dashboard/app/components/LeftSidebarNav.css
index 756d8bf525..dae2fb7773 100644
--- a/packages/dashboard/app/components/LeftSidebarNav.css
+++ b/packages/dashboard/app/components/LeftSidebarNav.css
@@ -290,8 +290,20 @@ The footer has no top divider; it remains a functional footer cluster but should
   justify-content: center;
 }
 
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+Width-only hide was wrong for tablet-class devices in the 601–768 CSS px band: JS mounts the left sidebar (mode=tablet) while this media query hid it and MobileNavBar returned null — operators lost every primary nav surface. Prefer the published viewport mode; keep the width rule as a no-JS/first-paint fallback for true phones.
+*/
 @media (max-width: 768px) {
   .left-sidebar-nav {
     display: none;
   }
 }
+
+html[data-viewport-mode="mobile"] .left-sidebar-nav {
+  display: none;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .left-sidebar-nav {
+  display: flex;
+}
diff --git a/packages/dashboard/app/components/MobileNavBar.css b/packages/dashboard/app/components/MobileNavBar.css
index 12cd2c2a3c..807e780897 100644
--- a/packages/dashboard/app/components/MobileNavBar.css
+++ b/packages/dashboard/app/components/MobileNavBar.css
@@ -44,6 +44,10 @@
   box-shadow: var(--shadow-md);
 }
 
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+Show the bottom tab bar only when JS mode is mobile. Width-only `@media (max-width: 768px)` left a gap on tablet-class narrow viewports (mode=tablet mounts no MobileNavBar, CSS still reserved its height under the elevated footer). Also reveal the bar for landscape phones that stay mode=mobile above 768 CSS px. Keep the width media query as a no-JS/first-paint fallback for true phones.
+*/
 @media (max-width: 768px) {
   .mobile-nav-bar {
     display: flex;
@@ -82,6 +86,47 @@
   }
 }
 
+html[data-viewport-mode="mobile"] .mobile-nav-bar {
+  display: flex;
+}
+
+html[data-viewport-mode="mobile"] .mobile-nav-bar--with-footer {
+  bottom: var(--icb-bottom-offset, 0px);
+}
+
+html[data-viewport-mode="mobile"] .mobile-nav-bar.mobile-nav-bar--keyboard-open,
+html[data-viewport-mode="mobile"] .mobile-nav-bar.mobile-nav-bar--with-footer.mobile-nav-bar--keyboard-open {
+  bottom: 0;
+  transform: translateY(100%);
+  pointer-events: none;
+}
+
+html[data-viewport-mode="mobile"] .project-content--with-mobile-nav:not(.project-content--with-footer) {
+  padding-bottom: calc(var(--mobile-nav-height) + max(env(safe-area-inset-bottom, 0px), 12px) + var(--standalone-bottom-gap) + var(--icb-bottom-offset, 0px));
+}
+
+html[data-viewport-mode="mobile"] .project-content--with-footer.project-content--with-mobile-nav {
+  padding-bottom: calc(
+    var(--executor-footer-height) + var(--mobile-nav-height) + max(env(safe-area-inset-bottom, 0px), 12px) + var(--standalone-bottom-gap) + var(--icb-bottom-offset, 0px)
+  );
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .mobile-nav-bar {
+  display: none;
+}
+
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+If a stale project-content--with-mobile-nav class remains while mode is tablet/desktop, do not reserve phantom tab-bar stack space — only the desktop footer token applies.
+*/
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .project-content--with-mobile-nav:not(.project-content--with-footer) {
+  padding-bottom: 0;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .project-content--with-footer.project-content--with-mobile-nav {
+  padding-bottom: var(--executor-footer-height);
+}
+
 /* Individual tab button */
 /*
 FNXC:MobileNav 2026-06-20-02:04:
diff --git a/packages/dashboard/app/components/ProjectSelector.css b/packages/dashboard/app/components/ProjectSelector.css
index 17d79b7467..f8e9343cb3 100644
--- a/packages/dashboard/app/components/ProjectSelector.css
+++ b/packages/dashboard/app/components/ProjectSelector.css
@@ -698,3 +698,24 @@
     display: none;
   }
 }
+
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+ProjectSelector.css loads after ExecutorStatusBar.css, so reassert the desktop footer token for tablet/desktop mode after the mobile width override above — otherwise mid-tablet still reserves the taller mobile footer while the bar sits at bottom:0. Also un-hide the project selector for tablet-class ≤768 CSS px (width media hid it with true phones).
+*/
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .project-content--with-footer,
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .dashboard-project-shell {
+  --executor-footer-height: 36px;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .project-selector {
+  display: inline-flex;
+}
+
+html[data-viewport-mode="mobile"] .project-content--with-footer {
+  --executor-footer-height: calc(var(--space-lg) * 2 + var(--space-xs));
+}
+
+html[data-viewport-mode="mobile"] .project-selector {
+  display: none;
+}
diff --git a/packages/dashboard/app/components/RightDock.css b/packages/dashboard/app/components/RightDock.css
index e9073aecc8..285bf29833 100644
--- a/packages/dashboard/app/components/RightDock.css
+++ b/packages/dashboard/app/components/RightDock.css
@@ -258,8 +258,20 @@ wide child cannot collapse the flex line.
   min-block-size: 0;
 }
 
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+Right dock hide follows JS viewport mode (authoritative mobile gate) rather than width alone, matching LeftSidebarNav/MobileNavBar so tablet-class narrow viewports keep the dock when mode=tablet. Width media remains a no-JS/first-paint fallback for true phones.
+*/
 @media (max-width: 768px) {
   .right-dock {
     display: none;
   }
 }
+
+html[data-viewport-mode="mobile"] .right-dock {
+  display: none;
+}
+
+html:is([data-viewport-mode="tablet"], [data-viewport-mode="desktop"]) .right-dock {
+  display: flex;
+}
diff --git a/packages/dashboard/app/hooks/__tests__/useViewportMode.test.ts b/packages/dashboard/app/hooks/__tests__/useViewportMode.test.ts
index 395705116b..ba3dc5be50 100644
--- a/packages/dashboard/app/hooks/__tests__/useViewportMode.test.ts
+++ b/packages/dashboard/app/hooks/__tests__/useViewportMode.test.ts
@@ -1,6 +1,15 @@
 import { act, renderHook } from "@testing-library/react";
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { getViewportMode, isFullScreenSheetViewport, isMobileViewport, isTabletTouchViewport, MOBILE_MEDIA_QUERY, useViewportMode } from "../useViewportMode";
+import {
+  getViewportMode,
+  isFullScreenSheetViewport,
+  isMobileViewport,
+  isTabletTouchViewport,
+  MOBILE_MEDIA_QUERY,
+  publishViewportMode,
+  useViewportMode,
+  VIEWPORT_MODE_DATASET_KEY,
+} from "../useViewportMode";
 
 const TABLET_MEDIA_QUERY = "(min-width: 769px) and (max-width: 1024px)";
 const MOBILE_WIDTH_MEDIA_QUERY = "(max-width: 768px)";
@@ -110,11 +119,29 @@ function createViewportMediaMock(initial: { mobile: boolean; tablet: boolean })
 describe("useViewportMode", () => {
   afterEach(() => {
     vi.unstubAllGlobals();
+    delete document.documentElement.dataset[VIEWPORT_MODE_DATASET_KEY];
     if (originalScreenDescriptor) {
       Object.defineProperty(window, "screen", originalScreenDescriptor);
     }
   });
 
+  it("publishViewportMode mirrors mode onto documentElement dataset", () => {
+    publishViewportMode("tablet");
+    expect(document.documentElement.dataset[VIEWPORT_MODE_DATASET_KEY]).toBe("tablet");
+    publishViewportMode("mobile");
+    expect(document.documentElement.dataset[VIEWPORT_MODE_DATASET_KEY]).toBe("mobile");
+  });
+
+  it("useViewportMode publishes data-viewport-mode for CSS chrome alignment", () => {
+    stubScreen(1024, 768);
+    installViewportMedia({ width: false, height: false, tablet: true });
+
+    const { result, unmount } = renderHook(() => useViewportMode());
+    expect(result.current).toBe("tablet");
+    expect(document.documentElement.dataset[VIEWPORT_MODE_DATASET_KEY]).toBe("tablet");
+    unmount();
+  });
+
   it("treats short landscape phones as mobile", () => {
     stubScreen(844, 390);
     vi.stubGlobal(
diff --git a/packages/dashboard/app/hooks/useViewportMode.ts b/packages/dashboard/app/hooks/useViewportMode.ts
index de8a4678b5..1c83065102 100644
--- a/packages/dashboard/app/hooks/useViewportMode.ts
+++ b/packages/dashboard/app/hooks/useViewportMode.ts
@@ -1,7 +1,19 @@
-import { useState, useEffect } from "react";
+import { useState, useEffect, useLayoutEffect } from "react";
 
 export type ViewportMode = "mobile" | "tablet" | "desktop";
 
+/*
+FNXC:ViewportChrome 2026-08-03-00:13:
+Shell chrome (left sidebar, mobile tab bar, footer stacking above the tab bar) must follow the JS viewport mode, not pure CSS width. Tablet-class devices at ≤768 CSS px are mode=tablet (sidebar on, no bottom tab bar) while `@media (max-width: 768px)` still hid the sidebar and elevated the footer for a phantom mobile nav — missing tab bar + mid-page overlapping footer. Publish the mode on `document.documentElement` so co-located CSS can override width-only rules and keep left sidebar + footer-at-bottom on tablet.
+*/
+export const VIEWPORT_MODE_DATASET_KEY = "viewportMode";
+
+/** Mirrors the resolved viewport mode onto `<html data-viewport-mode="…">` for CSS chrome alignment. */
+export function publishViewportMode(mode: ViewportMode): void {
+  if (typeof document === "undefined") return;
+  document.documentElement.dataset[VIEWPORT_MODE_DATASET_KEY] = mode;
+}
+
 // `(max-height: 480px)` catches phones held in landscape, which can exceed
 // 768 CSS px wide but stay short. Without it, landscape phones fall out of
 // mobile mode and lose the bottom nav bar + get the desktop horizontally-
@@ -153,7 +165,23 @@ export function isTabletTouchViewport(mode = getViewportMode()): boolean {
 }
 
 export function useViewportMode(): ViewportMode {
-  const [mode, setMode] = useState<ViewportMode>(getViewportMode);
+  /*
+  FNXC:ViewportChrome 2026-08-03-00:17:
+  Lazy initial state still runs publishViewportMode during the first render so the first paint already has data-viewport-mode — useLayoutEffect alone still leaves a pre-hydration/SSR-empty frame where width-only CSS hides the tablet sidebar.
+  */
+  const [mode, setMode] = useState<ViewportMode>(() => {
+    const initial = getViewportMode();
+    publishViewportMode(initial);
+    return initial;
+  });
+
+  /*
+  FNXC:ViewportChrome 2026-08-03-00:13:
+  Re-publish on every mode change before paint so resize/orientation updates do not flash phone chrome (hidden sidebar + elevated footer) on a tablet-class narrow viewport.
+  */
+  useLayoutEffect(() => {
+    publishViewportMode(mode);
+  }, [mode]);
 
   useEffect(() => {
     if (typeof window === "undefined") return;