diff --git a/src/web/public/app.js b/src/web/public/app.js
index 6b1e59ae..b5075b32 100644
--- a/src/web/public/app.js
+++ b/src/web/public/app.js
@@ -525,6 +525,56 @@ const DEFAULT_SHORTCUTS = [
     bindings: [{ modifiers: ['alt'], key: 'b', code: 'KeyB' }],
     action: 'toggleSessionSidebar',
   },
+  // Tile grid (tile-grid.js). Dispatched by tileShortcutFor()/runTileShortcut()
+  // and deliberately absent from SHORTCUT_ACTIONS: each applies only in some
+  // states (the focus chords only while the grid is open), and outside them the
+  // chord must reach the terminal untouched. Every xterm key handler swallows a
+  // chord that applies, so it never reaches a PTY. Defaults: Ctrl+Shift+G makes
+  // xterm emit nothing (a shifted Ctrl letter) and overrides only the browser's
+  // find-previous; Alt+Shift+Arrows are bound by no CLI Codeman runs.
+  {
+    id: 'toggle-tile-grid',
+    group: 'Tiles',
+    label: 'Toggle Tile Grid',
+    bindings: [{ modifiers: ['ctrl', 'shift'], key: 'G', code: 'KeyG' }],
+    action: 'toggleTileGrid',
+  },
+  {
+    id: 'focus-tile-left',
+    group: 'Tiles',
+    label: 'Focus Tile Left',
+    bindings: [{ modifiers: ['alt', 'shift'], key: 'ArrowLeft' }],
+    action: 'focusTileLeft',
+  },
+  {
+    id: 'focus-tile-right',
+    group: 'Tiles',
+    label: 'Focus Tile Right',
+    bindings: [{ modifiers: ['alt', 'shift'], key: 'ArrowRight' }],
+    action: 'focusTileRight',
+  },
+  {
+    id: 'focus-tile-up',
+    group: 'Tiles',
+    label: 'Focus Tile Up',
+    bindings: [{ modifiers: ['alt', 'shift'], key: 'ArrowUp' }],
+    action: 'focusTileUp',
+  },
+  {
+    id: 'focus-tile-down',
+    group: 'Tiles',
+    label: 'Focus Tile Down',
+    bindings: [{ modifiers: ['alt', 'shift'], key: 'ArrowDown' }],
+    action: 'focusTileDown',
+  },
+  {
+    id: 'remove-tile',
+    group: 'Tiles',
+    label: 'Remove Focused Tile',
+    // Unbound by default; the session keeps running either way.
+    bindings: [],
+    action: 'removeTile',
+  },
   {
     id: 'previous-next-session',
     group: 'Session',
@@ -1362,6 +1412,15 @@ class CodemanApp {
         }
       }
 
+      // Tile grid chords: only where they apply (tile-grid.js tileShortcutFor),
+      // so outside the grid Alt+Shift+Arrows still reach the terminal.
+      const tileShortcut = this.tileShortcutFor?.(e);
+      if (tileShortcut) {
+        e.preventDefault();
+        this.runTileShortcut(tileShortcut);
+        return;
+      }
+
       // Match against the shortcut registry so user rebinds and per-shortcut
       // disables (App Settings → Shortcuts) take effect. Every dispatchable
       // binding requires Ctrl/Cmd/Alt (capture enforces the same), so plain
diff --git a/src/web/public/styles.css b/src/web/public/styles.css
index ab9f2f73..0bee818a 100644
--- a/src/web/public/styles.css
+++ b/src/web/public/styles.css
@@ -2510,6 +2510,12 @@ html[data-tab-orientation='vertical'].tab-rail-compact
   display: none !important;
 }
 
+/* The tile grid is open (tile-grid.js): the split cannot open beside it. */
+.btn-split.btn-split--blocked {
+  opacity: 0.4;
+  cursor: not-allowed;
+}
+
 /* While a split is open, the button's own click closes it instead of opening
    the picker — the accent fill is what tells the user which of its two
    behaviours the next click will get (aria-pressed carries the same state
diff --git a/src/web/public/terminal-split.js b/src/web/public/terminal-split.js
index 8a5d839b..70df4081 100644
--- a/src/web/public/terminal-split.js
+++ b/src/web/public/terminal-split.js
@@ -46,6 +46,9 @@ Object.assign(CodemanApp.prototype, {
     // the old exact-node check below) bubbled straight through to
     // `document` and self-closed the menu it just opened.
     event?.stopPropagation();
+    // The tile grid and the split are never open together (tile-grid.js); the
+    // Split button shows as unavailable meanwhile.
+    if (this._tilesOwnTerminal?.()) return;
     if (this._splitPane) {
       this.closeSplitPane();
       return;
@@ -139,6 +142,8 @@ Object.assign(CodemanApp.prototype, {
     // see _applySplitButtonVisibility's comment for why both a JS check and
     // a CSS backstop exist.
     if (window.innerWidth < SPLIT_PANE_MIN_WIDTH) return;
+    // Never beside the tile grid: the main terminal is parked while it is open.
+    if (this._tilesOwnTerminal?.()) return;
     // No active session means there is no `.terminal-wrap` to split against
     // (the welcome overlay is showing) — without this, a split opened from
     // the home screen still created the container and connected Pane B, just
diff --git a/src/web/public/terminal-tile.js b/src/web/public/terminal-tile.js
index 76b3b445..6424ab7b 100644
--- a/src/web/public/terminal-tile.js
+++ b/src/web/public/terminal-tile.js
@@ -208,6 +208,10 @@
         if (ev.type === 'keydown' && global.app?.shouldToggleSessionSidebarFromShortcut?.(ev)) {
           return false;
         }
+        // Tile grid chords (focus, toggle): acted on by the capture handler, so
+        // they must never reach this tile's PTY. Every event type, and before
+        // the Shift+Enter branch below.
+        if (global.app?.tileShortcutFor?.(ev)) return false;
         // Ctrl+V / Cmd+V: the primary pane's paste trap, aimed at THIS pane, so
         // a pasted image uploads to this pane's session and its path is typed
         // here, and pasted text goes into this xterm with its bracketed-paste
diff --git a/src/web/public/terminal-ui.js b/src/web/public/terminal-ui.js
index d11e7f92..4dfa7364 100644
--- a/src/web/public/terminal-ui.js
+++ b/src/web/public/terminal-ui.js
@@ -590,6 +590,11 @@ Object.assign(CodemanApp.prototype, {
         return false;
       }
 
+      // Tile grid chords (Ctrl+Shift+G, Alt+Shift+Arrows): the capture handler
+      // has already acted on one that applies, and its preventDefault() does not
+      // stop xterm. Every event type, and BEFORE the Shift+Enter branch below.
+      if (this.tileShortcutFor?.(ev)) return false;
+
       // Smart copy (#211): with a selection, Ctrl+C copies it instead of sending
       // ^C. With NO selection the branch must fall through (return true, and no
       // preventDefault) or the interrupt key is lost, which is the whole reason
diff --git a/src/web/public/tile-grid.js b/src/web/public/tile-grid.js
index bc96e631..1c7eca2a 100644
--- a/src/web/public/tile-grid.js
+++ b/src/web/public/tile-grid.js
@@ -26,6 +26,16 @@ const TILE_GRID_FONT_KEY = 'codeman-tile-font-size';
 // Trailing debounce for refitting tiles after the grid area changes size, so a
 // window drag sends each tile's PTY one resize, not one per frame.
 const TILE_GRID_REFIT_MS = 150;
+// Registry ids of the tile chords (DEFAULT_SHORTCUTS, app.js), and whether each
+// needs the grid open. The toggle applies wherever a grid could open.
+const TILE_SHORTCUTS = {
+  'toggle-tile-grid': { needsOpen: false },
+  'focus-tile-left': { needsOpen: true, direction: 'left' },
+  'focus-tile-right': { needsOpen: true, direction: 'right' },
+  'focus-tile-up': { needsOpen: true, direction: 'up' },
+  'focus-tile-down': { needsOpen: true, direction: 'down' },
+  'remove-tile': { needsOpen: true },
+};
 
 /** The grid's state. `has(id)` answers only while it is open. */
 class TileGridModel {
@@ -137,8 +147,18 @@ Object.assign(CodemanApp.prototype, {
     if (!this.canOpenTileGrid()) return false;
     const grid = (this._tileGrid ||= new TileGridModel());
     const max = window.CodemanTileGrid.TILE_GRID_MAX;
+    // The grid and the split are never open together. An open split becomes the
+    // grid's first two tiles (Pane A focused, Pane B beside it), so "split, then
+    // want more" is one step. No closing resize for Pane A: it is about to park.
+    let requested = ids || [];
+    if (this._splitPane) {
+      const seed = [this.activeSessionId, this._splitSessionId].filter(Boolean);
+      this.closeSplitPane({ skipPrimaryResize: true });
+      requested = [...seed, ...requested];
+      if (!requested.includes(focusedId)) focusedId = seed[0] ?? null;
+    }
     const wanted = [];
-    for (const id of ids || []) {
+    for (const id of requested) {
       if (typeof id !== 'string' || wanted.includes(id)) continue;
       if (!this.sessions.has(id) || this.detachedSessions?.has(id)) continue;
       wanted.push(id);
@@ -175,6 +195,7 @@ Object.assign(CodemanApp.prototype, {
     this._installTileGridWidthGate();
     this._selectTiledSession(focus, { auto });
     this._updateConnectionIndicator?.();
+    this._updateSplitButtonForTiles();
     return true;
   },
 
@@ -230,9 +251,95 @@ Object.assign(CodemanApp.prototype, {
       this.terminalBufferCache?.delete(id);
     }
     this._updateConnectionIndicator?.();
+    this._updateSplitButtonForTiles();
     if (reselect) this._selectAfterTileGrid(focusedId);
   },
 
+  // The Split button cannot act while the grid is open (openSplitPicker and
+  // openSplitPane refuse), so it says so: aria-disabled plus a title, the same
+  // refusal the split already gives for web tabs and the welcome screen.
+  _updateSplitButtonForTiles() {
+    const btn = document.querySelector('.btn-split');
+    if (!btn) return;
+    const blocked = this._tilesOwnTerminal();
+    btn.classList.toggle('btn-split--blocked', blocked);
+    btn.setAttribute('aria-disabled', blocked ? 'true' : 'false');
+    if (blocked) {
+      btn.title = 'Split: unavailable while tiles are open';
+      btn.setAttribute('aria-label', btn.title);
+    } else {
+      this._updateSplitButtonState?.(!!this._splitPane);
+    }
+  },
+
+  /**
+   * The tile chord `e` asks for, if it applies right now, else null: the toggle
+   * wherever a grid could open (or is open), the focus and remove chords only
+   * while it is open, so outside the grid they reach the terminal untouched.
+   * Registry-aware (rebinds and disables in App Settings, Shortcuts). The
+   * capture handler (app.js) dispatches it; every xterm key handler returns
+   * false for it, so a chord that applies never reaches a PTY.
+   *
+   * @returns {string|null} the registry id
+   */
+  tileShortcutFor(e) {
+    if (!e || (!e.ctrlKey && !e.metaKey && !e.altKey)) return null;
+    if (typeof this.getShortcutRegistry !== 'function' || typeof this.matchesShortcutEvent !== 'function') return null;
+    const open = this._tilesOwnTerminal();
+    for (const shortcut of this.getShortcutRegistry()) {
+      const spec = TILE_SHORTCUTS[shortcut.id];
+      if (!spec || shortcut.disabled || !this.matchesShortcutEvent(e, shortcut)) continue;
+      if (spec.needsOpen ? open : open || this.canOpenTileGrid()) return shortcut.id;
+      return null;
+    }
+    return null;
+  },
+
+  /** Runs a chord tileShortcutFor() matched. */
+  runTileShortcut(id) {
+    const spec = TILE_SHORTCUTS[id];
+    if (!spec) return;
+    if (id === 'toggle-tile-grid') this.toggleTileGrid();
+    else if (id === 'remove-tile') this.removeFocusedTile();
+    else if (spec.direction) this.focusTileInDirection(spec.direction);
+  },
+
+  /**
+   * Opens the grid, or closes it to the single view of the focused session.
+   * Opening brings back the grid this tab last left (decision 1: one step back
+   * after a selection outside it), else an open split as two tiles, else the
+   * active session as one tile.
+   */
+  toggleTileGrid() {
+    if (this._tilesOwnTerminal()) {
+      this.closeTileGrid({ keepStored: true, reselect: true });
+      return;
+    }
+    if (!this.canOpenTileGrid()) return;
+    const remembered = this._tileGridRemembered;
+    const ids = (remembered?.ids || []).filter((id) => this.sessions.has(id) && !this.detachedSessions?.has(id));
+    if (ids.length > 0) {
+      this.openTileGrid(ids, { focusedId: remembered.focusedId, auto: true });
+      return;
+    }
+    if (this.activeSessionId) this.openTileGrid([this.activeSessionId], { focusedId: this.activeSessionId });
+  },
+
+  /** Alt+Shift+Arrows: a human selection of the tile in that direction. */
+  focusTileInDirection(direction) {
+    const grid = this._tileGrid;
+    if (!grid?.open) return;
+    const id = window.CodemanTileGrid.tileInDirection(grid.ids, grid.focusedId, direction, grid.cols);
+    if (id) this.selectSession(id);
+  },
+
+  /** Removes the focused tile (the session keeps running); a neighbour takes focus. */
+  removeFocusedTile() {
+    const grid = this._tileGrid;
+    if (!grid?.open || !grid.focusedId) return;
+    this.removeTile(grid.focusedId, { refocus: true, auto: true });
+  },
+
   // The single view after the grid closes: the session the grid was focused on,
   // replayed fresh (forceReload drops the stale snapshot and nulls
   // activeSessionId BEFORE _cleanupPreviousSession, so nothing wrong is saved),
diff --git a/test/mocks/tile-grid-vm.ts b/test/mocks/tile-grid-vm.ts
index bb85244a..e26ac6dc 100644
--- a/test/mocks/tile-grid-vm.ts
+++ b/test/mocks/tile-grid-vm.ts
@@ -1,7 +1,7 @@
 /**
  * @fileoverview A `vm` harness for the tile grid (tile-grid.js) with the real
- * app around it: constants.js + app.js + terminal-ui.js + tile-grid.js in one
- * context, a small fake DOM (just what the grid touches) and a fake
+ * app around it: constants.js + app.js + terminal-ui.js + terminal-split.js +
+ * tile-grid.js in one context, a small fake DOM (just what the grid touches) and a fake
  * TerminalTile that records what the grid asks of it.
  *
  * `makeGridApp()` returns an app instance with everything around the grid that
@@ -57,7 +57,8 @@ export class FakeEl {
   remove() {
     if (!this.parentElement) return;
     const siblings = this.parentElement.children;
-    siblings.splice(siblings.indexOf(this), 1);
+    const i = siblings.indexOf(this);
+    if (i !== -1) siblings.splice(i, 1);
     this.parentElement = null;
   }
   setAttribute(k: string, v: string) {
@@ -76,7 +77,15 @@ export class FakeEl {
   getBoundingClientRect() {
     return { width: 2400, height: 1200, top: 0, left: 0, right: 2400, bottom: 1200 };
   }
-  querySelector() {
+  /** `.class` selectors only: the first descendant carrying that class. */
+  querySelector(sel: string): FakeEl | null {
+    if (!sel.startsWith('.') || /[\s[>:]/.test(sel)) return null;
+    const cls = sel.slice(1);
+    for (const child of this.children) {
+      if (child.classList.contains(cls)) return child;
+      const deeper = child.querySelector(sel);
+      if (deeper) return deeper;
+    }
     return null;
   }
 }
@@ -117,6 +126,11 @@ section.id = 'tileGrid';
 section.className = 'tile-grid';
 main.appendChild(section);
 
+/** Extra elements `document.querySelector` finds, by exact selector (e.g. '.btn-split'). */
+export const bySelector = new Map<string, FakeEl>();
+export const body = new FakeEl();
+/** `document.addEventListener`, so a test can find a listener the app installed. */
+export const documentAddEventListener = vi.fn();
 export const localStore = new Map<string, string>();
 /** What the code under test deferred with requestIdleCallback; a test runs them. */
 export const idleCallbacks: Array<() => void> = [];
@@ -145,11 +159,13 @@ const context = vm.createContext({
   location: { protocol: 'http:', host: 'codeman.test', pathname: '/', search: '', hash: '' },
   history: { replaceState: vi.fn(), state: null },
   document: {
-    addEventListener: vi.fn(),
+    addEventListener: documentAddEventListener,
     documentElement: { dataset: {} },
     createElement: () => new FakeEl(),
     getElementById: (id: string) => (id === 'tileGrid' ? section : null),
-    querySelector: (sel: string) => (sel === '.main' ? main : sel === '.terminal-wrap' ? wrap : null),
+    body,
+    querySelector: (sel: string) =>
+      sel === '.main' ? main : sel === '.terminal-wrap' ? wrap : (bySelector.get(sel) ?? null),
     querySelectorAll: () => [],
   },
   localStorage: {
@@ -162,7 +178,8 @@ const context = vm.createContext({
   MobileDetection: { isTouchDevice: () => false, isHandheldDevice: () => false, getDeviceType: () => 'desktop' },
 });
 vm.runInContext(
-  `${read('constants.js')}\n${read('app.js')}\n${read('terminal-ui.js')}\n${read('tile-grid.js')}\n` +
+  `${read('constants.js')}\n${read('app.js')}\n${read('terminal-ui.js')}\n${read('terminal-split.js')}\n` +
+    `${read('tile-grid.js')}\n` +
     'globalThis.__CodemanApp = CodemanApp;',
   context
 );
@@ -237,4 +254,10 @@ export function resetGridHarness() {
   windowStub.innerWidth = 2400;
   section.children = [];
   main.className = 'main';
+  // A split a test left open moved .terminal-wrap into its container.
+  main.children = [];
+  main.appendChild(wrap);
+  main.appendChild(section);
+  bySelector.clear();
+  body.children = [];
 }
diff --git a/test/tile-grid-shortcuts.test.ts b/test/tile-grid-shortcuts.test.ts
new file mode 100644
index 00000000..afd7e493
--- /dev/null
+++ b/test/tile-grid-shortcuts.test.ts
@@ -0,0 +1,331 @@
+/**
+ * @fileoverview The tile grid's chords: registry entries, when they apply, and
+ * that a chord which applies never reaches a PTY.
+ *
+ * Defaults (all rebindable in App Settings, Shortcuts): Ctrl+Shift+G toggles
+ * the grid, Alt+Shift+Arrows move focus between tiles, Remove Focused Tile is
+ * unbound. The toggle applies wherever a grid could open; the focus and remove
+ * chords only while the grid is open, so outside it Alt+Shift+Arrows reach the
+ * terminal untouched. The capture-phase handler (app.js) dispatches a chord
+ * that applies; its preventDefault() does not stop xterm, so every xterm key
+ * handler (the main terminal's and TerminalTile's) returns false for it too,
+ * for every event type and before the Shift+Enter gate (which would otherwise
+ * send S-Enter for Alt+Shift+Enter style chords).
+ *
+ * Real code: the grid harness (test/mocks/tile-grid-vm.ts) for the registry,
+ * the capture handler and the actions; a second `vm` context with the real
+ * TerminalTile for its key handler; the main terminal's handler, which needs a
+ * real xterm, is pinned at the source. Port: N/A.
+ */
+import { readFileSync } from 'node:fs';
+import { performance } from 'node:perf_hooks';
+import { resolve } from 'node:path';
+import vm from 'node:vm';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import {
+  documentAddEventListener,
+  makeGridApp,
+  resetGridHarness,
+  windowStub as gridWindow,
+  type GridApp,
+} from './mocks/tile-grid-vm.js';
+
+const IDS = ['s-a', 's-b', 's-c'];
+const read = (f: string) => readFileSync(resolve(import.meta.dirname, `../src/web/public/${f}`), 'utf8');
+
+const chord = (overrides: Record<string, unknown>) => ({
+  type: 'keydown',
+  key: '',
+  code: '',
+  ctrlKey: false,
+  metaKey: false,
+  shiftKey: false,
+  altKey: false,
+  preventDefault: vi.fn(),
+  target: { closest: () => null },
+  ...overrides,
+});
+const TOGGLE = { key: 'G', code: 'KeyG', ctrlKey: true, shiftKey: true };
+const RIGHT = { key: 'ArrowRight', code: 'ArrowRight', altKey: true, shiftKey: true };
+
+beforeEach(() => {
+  resetGridHarness();
+});
+
+describe('registry', () => {
+  it('ships the tile chords, rebindable, with Remove Focused Tile unbound', () => {
+    const app = makeGridApp(IDS);
+    const byId = Object.fromEntries(app.getShortcutRegistry().map((s: { id: string }) => [s.id, s])) as Record<
+      string,
+      { bindings: Array<Record<string, unknown>>; group: string }
+    >;
+    expect(byId['toggle-tile-grid'].bindings).toEqual([{ modifiers: ['ctrl', 'shift'], key: 'G', code: 'KeyG' }]);
+    for (const dir of ['Left', 'Right', 'Up', 'Down']) {
+      expect(byId[`focus-tile-${dir.toLowerCase()}`].bindings).toEqual([
+        { modifiers: ['alt', 'shift'], key: `Arrow${dir}` },
+      ]);
+    }
+    expect(byId['remove-tile'].bindings).toEqual([]);
+    expect(byId['toggle-tile-grid'].group).toBe('Tiles');
+  });
+});
+
+describe('when a chord applies', () => {
+  it('the toggle applies wherever a grid could open, and while one is open', () => {
+    const app = makeGridApp(IDS);
+    expect(app.tileShortcutFor(chord(TOGGLE))).toBe('toggle-tile-grid');
+    app.openTileGrid(IDS);
+    expect(app.tileShortcutFor(chord(TOGGLE))).toBe('toggle-tile-grid');
+  });
+
+  it('the toggle does not apply in a narrow window or a solo window', () => {
+    const app = makeGridApp(IDS);
+    gridWindow.innerWidth = 1000;
+    expect(app.tileShortcutFor(chord(TOGGLE))).toBeNull();
+    gridWindow.innerWidth = 2400;
+    app.isSoloWindow = true;
+    expect(app.tileShortcutFor(chord(TOGGLE))).toBeNull();
+  });
+
+  it('the focus chords apply only while the grid is open', () => {
+    const app = makeGridApp(IDS);
+    expect(app.tileShortcutFor(chord(RIGHT))).toBeNull();
+    app.openTileGrid(IDS);
+    expect(app.tileShortcutFor(chord(RIGHT))).toBe('focus-tile-right');
+  });
+
+  it('plain typing and unrelated chords never match', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS);
+    expect(app.tileShortcutFor(chord({ key: 'g', code: 'KeyG' }))).toBeNull();
+    expect(app.tileShortcutFor(chord({ key: 'ArrowRight', altKey: true }))).toBeNull();
+    expect(app.tileShortcutFor(chord({ key: 'G', code: 'KeyG', ctrlKey: true }))).toBeNull();
+  });
+
+  it('honours a disable and a rebind from App Settings', () => {
+    const app = makeGridApp(IDS);
+    app.loadAppSettingsFromStorage = () => ({
+      shortcutOverrides: {
+        'toggle-tile-grid': { disabled: true },
+        'focus-tile-right': { bindings: [{ modifiers: ['ctrl', 'alt'], key: 'l', code: 'KeyL' }] },
+      },
+    });
+    expect(app.tileShortcutFor(chord(TOGGLE))).toBeNull();
+    app.openTileGrid(IDS);
+    expect(app.tileShortcutFor(chord(RIGHT))).toBeNull();
+    expect(app.tileShortcutFor(chord({ key: 'l', code: 'KeyL', ctrlKey: true, altKey: true }))).toBe(
+      'focus-tile-right'
+    );
+  });
+});
+
+describe('the capture-phase handler', () => {
+  function handlerFor(app: GridApp) {
+    app.$ = () => null;
+    app.setupColorPicker = vi.fn();
+    const before = (documentAddEventListener.mock.calls as unknown[]).length;
+    app.setupEventListeners();
+    const added = (documentAddEventListener.mock.calls as Array<[string, (e: unknown) => void, boolean]>).slice(before);
+    const keydown = added.find(([type, , capture]) => type === 'keydown' && capture === true);
+    if (!keydown) throw new Error('no capture-phase keydown listener');
+    return keydown[1];
+  }
+
+  it('Ctrl+Shift+G opens the grid on the active session, then closes it, overriding the browser', () => {
+    const app = makeGridApp(IDS);
+    app.selectSession = vi.fn();
+    const onKeydown = handlerFor(app);
+    const open = chord(TOGGLE);
+    onKeydown(open);
+    expect(open.preventDefault).toHaveBeenCalled();
+    expect(app._tileGrid.ids).toEqual(['s-a']);
+
+    onKeydown(chord(TOGGLE));
+    expect(app._tilesOwnTerminal()).toBe(false);
+    expect(app.selectSession).toHaveBeenCalledWith('s-a', { forceReload: true, auto: true });
+  });
+
+  it('Alt+Shift+Right moves focus to the tile on the right, as a human selection', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS);
+    app.markIdleAlertSeen.mockClear();
+    // The real selectSession routes a tiled id to the tile branch.
+    delete app.selectSession;
+    const onKeydown = handlerFor(app);
+    const e = chord(RIGHT);
+    onKeydown(e);
+    expect(e.preventDefault).toHaveBeenCalled();
+    expect(app.activeSessionId).toBe('s-b');
+    expect(app.markIdleAlertSeen).toHaveBeenCalledWith('s-b');
+  });
+
+  it('outside the grid Alt+Shift+Right is left alone for the terminal', () => {
+    const app = makeGridApp(IDS);
+    const onKeydown = handlerFor(app);
+    const e = chord(RIGHT);
+    onKeydown(e);
+    expect(e.preventDefault).not.toHaveBeenCalled();
+    expect(app._tilesOwnTerminal()).toBe(false);
+  });
+});
+
+describe('the actions', () => {
+  it('the toggle brings back the grid this tab last left, focus included', () => {
+    const app = makeGridApp(IDS);
+    app.selectSession = vi.fn();
+    app.openTileGrid(IDS, { focusedId: 's-c' });
+    app.closeTileGrid({ reselect: false });
+    app.toggleTileGrid();
+    expect(app._tileGrid.ids).toEqual(IDS);
+    expect(app.activeSessionId).toBe('s-c');
+  });
+
+  it('a remembered tile whose session is gone is not brought back', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS);
+    app.closeTileGrid({ reselect: false });
+    app.sessions.delete('s-b');
+    app.toggleTileGrid();
+    expect(app._tileGrid.ids).toEqual(['s-a', 's-c']);
+  });
+
+  it('with every remembered session gone, it opens on the active session instead', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(['s-b', 's-c']);
+    app.closeTileGrid({ reselect: false });
+    app.sessions.delete('s-b');
+    app.sessions.delete('s-c');
+    app.activeSessionId = 's-a';
+    app.toggleTileGrid();
+    expect(app._tileGrid.ids).toEqual(['s-a']);
+  });
+
+  it('Remove Focused Tile removes it (the session keeps running) and a neighbour takes focus', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS, { focusedId: 's-b' });
+    app._apiDelete = vi.fn();
+    app.removeFocusedTile();
+    expect(app._tileGrid.ids).toEqual(['s-a', 's-c']);
+    expect(app.activeSessionId).toBe('s-c');
+    expect(app.sessions.has('s-b')).toBe(true);
+    expect(app._apiDelete).not.toHaveBeenCalled();
+  });
+});
+
+describe('xterm key handlers swallow a chord that applies', () => {
+  it("the main terminal's handler checks the chord before the Shift+Enter gate, for every event type", () => {
+    // That handler lives in initTerminal's closure over a real xterm, so the
+    // rule is pinned at the source, as terminal-copy-clean.test.ts does.
+    const src = read('terminal-ui.js');
+    const handler = src.slice(src.indexOf('this.terminal.attachCustomKeyEventHandler((ev) => {'));
+    const gate = handler.indexOf('if (this.tileShortcutFor?.(ev)) return false;');
+    const enter = handler.indexOf("if (ev.key === 'Enter' && (ev.shiftKey || ev.ctrlKey)) {");
+    expect(gate).toBeGreaterThan(0);
+    expect(gate).toBeLessThan(enter);
+  });
+
+  describe("TerminalTile's handler (real tile, real tileShortcutFor)", () => {
+    class FakeTerminal {
+      static last: FakeTerminal;
+      keyHandler: ((ev: Record<string, unknown>) => boolean) | null = null;
+      options: Record<string, unknown>;
+      cols = 80;
+      rows = 24;
+      buffer = { active: { type: 'normal', viewportY: 0, length: 24 } };
+      textarea = { addEventListener() {}, removeEventListener() {} };
+      constructor(options: Record<string, unknown>) {
+        this.options = options;
+        FakeTerminal.last = this;
+      }
+      loadAddon() {}
+      open() {}
+      onData() {}
+      attachCustomKeyEventHandler(fn: (ev: Record<string, unknown>) => boolean) {
+        this.keyHandler = fn;
+      }
+      registerLinkProvider() {}
+      write() {}
+      clear() {}
+      dispose() {}
+    }
+    const fetchMock = vi.fn(async () => ({ ok: true, json: async () => ({ data: { terminalBuffer: '' } }) }));
+    const windowStub: Record<string, unknown> = {
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+      CodemanBase: { base: '' },
+      innerWidth: 2400,
+    };
+    const context = vm.createContext({
+      console: { ...console, log: vi.fn(), debug: vi.fn() },
+      performance,
+      setInterval: vi.fn(),
+      clearInterval: vi.fn(),
+      setTimeout,
+      clearTimeout,
+      requestAnimationFrame: vi.fn(),
+      HTMLCanvasElement: class HTMLCanvasElement {},
+      WebSocket: class {
+        static OPEN = 1;
+        send() {}
+        close() {}
+      },
+      Terminal: FakeTerminal,
+      FitAddon: {
+        FitAddon: class {
+          fit() {}
+          proposeDimensions() {
+            return { cols: 80, rows: 24 };
+          }
+        },
+      },
+      fetch: fetchMock,
+      location: { protocol: 'http:', host: 'codeman.test' },
+      document: { addEventListener: vi.fn(), documentElement: { dataset: {} } },
+      localStorage: { getItem: vi.fn(), setItem: vi.fn(), removeItem: vi.fn() },
+      window: windowStub,
+      MobileDetection: { isTouchDevice: () => false, isHandheldDevice: () => false, getDeviceType: () => 'desktop' },
+    });
+    vm.runInContext(
+      `${read('constants.js')}\n${read('app.js')}\n${read('terminal-ui.js')}\n${read('terminal-tile.js')}\n` +
+        `${read('terminal-split.js')}\n${read('tile-grid.js')}\nglobalThis.__CodemanApp = CodemanApp;`,
+      context
+    );
+    const App = (context as unknown as { __CodemanApp: { prototype: object } }).__CodemanApp;
+    const TerminalTile = windowStub.TerminalTile as new (
+      id: string,
+      mount: unknown,
+      opts: object
+    ) => { connect(): Promise<void>; destroy(): void };
+
+    async function tileHandler(gridOpen: boolean) {
+      const app = Object.create(App.prototype) as GridApp;
+      app.loadAppSettingsFromStorage = () => ({});
+      app.isSoloWindow = false;
+      app._tileGrid = { open: gridOpen };
+      windowStub.app = app;
+      const tile = new TerminalTile('s1', { addEventListener() {}, removeEventListener() {} }, { mode: 'claude' });
+      await tile.connect();
+      const handler = FakeTerminal.last.keyHandler!;
+      tile.destroy();
+      return handler;
+    }
+
+    it.each(['keydown', 'keypress', 'keyup'])(
+      'returns false for Alt+Shift+Right (%s) while the grid is open',
+      async (type) => {
+        const handler = await tileHandler(true);
+        expect(handler({ ...chord(RIGHT), type })).toBe(false);
+      }
+    );
+
+    it('lets Alt+Shift+Right through to the PTY when no grid is open', async () => {
+      const handler = await tileHandler(false);
+      expect(handler(chord(RIGHT))).toBe(true);
+    });
+
+    it('returns false for the toggle chord', async () => {
+      const handler = await tileHandler(true);
+      expect(handler(chord(TOGGLE))).toBe(false);
+    });
+  });
+});
diff --git a/test/tile-grid-split-coexistence.test.ts b/test/tile-grid-split-coexistence.test.ts
new file mode 100644
index 00000000..2a82a5b6
--- /dev/null
+++ b/test/tile-grid-split-coexistence.test.ts
@@ -0,0 +1,124 @@
+/**
+ * @fileoverview The tile grid and the split pane are never open together.
+ *
+ * Both run on TerminalTile, and the split's wrappers (`selectSession`,
+ * `_onSessionDeleted` in terminal-split.js) key on `this._splitPane`, so they
+ * would fight the grid over the same terminal area if both were ever up:
+ *
+ * - opening the grid while a split is open closes the split first and seeds
+ *   the grid with both of its sessions, Pane A focused and Pane B beside it;
+ * - while the grid is open, `openSplitPicker` and `openSplitPane` refuse, and
+ *   the Split button says so (`aria-disabled`, a title);
+ * - closing the grid never reopens a split;
+ * - the split's wrappers stay inert while the grid is open.
+ *
+ * Real code: constants.js + app.js + terminal-ui.js + terminal-split.js +
+ * tile-grid.js (test/mocks/tile-grid-vm.ts). Port: N/A.
+ */
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import {
+  FakeEl,
+  FakeTile,
+  body,
+  bySelector,
+  main,
+  makeGridApp,
+  resetGridHarness,
+  type GridApp,
+} from './mocks/tile-grid-vm.js';
+
+const IDS = ['s-a', 's-b', 's-c'];
+
+function makeSplitButton() {
+  const btn = new FakeEl();
+  btn.className = 'btn-icon-header btn-split';
+  bySelector.set('.btn-split', btn);
+  return btn;
+}
+
+/** s-a in the main pane, s-b in Pane B (the split's real openSplitPane). */
+function openSplit(app: GridApp) {
+  app.openSplitPane('s-b');
+  expect(app._splitSessionId).toBe('s-b');
+  // closeSplitPane finds its container by selector.
+  const container = main.querySelector('.terminal-split-container');
+  if (container) bySelector.set('.terminal-split-container', container);
+  return FakeTile.all.at(-1) as FakeTile;
+}
+
+beforeEach(() => {
+  resetGridHarness();
+});
+
+describe('opening the grid over an open split', () => {
+  it('closes the split and seeds the grid with both of its sessions, Pane A focused', () => {
+    const app = makeGridApp(IDS);
+    const paneB = openSplit(app);
+
+    app.toggleTileGrid();
+
+    expect(paneB.destroy).toHaveBeenCalledTimes(1);
+    expect(app._splitPane).toBeNull();
+    expect(app._tileGrid.ids).toEqual(['s-a', 's-b']);
+    expect(app.activeSessionId).toBe('s-a');
+    // Pane A is about to park: no closing resize for it.
+    expect(app.sendResize).toHaveBeenCalledTimes(1); // the split's own opening resize only
+  });
+
+  it('an explicit open over a split keeps both split sessions first', () => {
+    const app = makeGridApp(IDS);
+    openSplit(app);
+    app.openTileGrid(['s-c']);
+    expect(app._tileGrid.ids).toEqual(['s-a', 's-b', 's-c']);
+    expect(app.activeSessionId).toBe('s-a');
+  });
+});
+
+describe('while the grid is open', () => {
+  it('the split refuses to open, from the picker or directly', () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS);
+    const before = FakeTile.all.length;
+
+    app.openSplitPicker({ stopPropagation: vi.fn() });
+    app.openSplitPane('s-b');
+
+    expect(app._splitPane ?? null).toBeNull();
+    expect(FakeTile.all.length).toBe(before);
+    // The picker itself never opened either.
+    expect(body.children).toHaveLength(0);
+    expect(app._splitPickerDismissHandlers ?? null).toBeNull();
+  });
+
+  it('the Split button is marked unavailable, and back to normal once the grid closes', () => {
+    const app = makeGridApp(IDS);
+    const btn = makeSplitButton();
+    app.openTileGrid(IDS);
+    expect(btn.getAttribute('aria-disabled')).toBe('true');
+    expect(btn.classList.contains('btn-split--blocked')).toBe(true);
+
+    app.closeTileGrid({ reselect: false });
+    expect(btn.getAttribute('aria-disabled')).toBe('false');
+    expect(btn.classList.contains('btn-split--blocked')).toBe(false);
+    expect(btn.getAttribute('aria-pressed')).toBe('false');
+  });
+
+  it("the split's wrappers do nothing (no split to close or promote)", () => {
+    const app = makeGridApp(IDS);
+    app.openTileGrid(IDS);
+    app.closeSplitPane = vi.fn();
+    app._onSessionDeleted({ id: 's-c' });
+    expect(app.closeSplitPane).not.toHaveBeenCalled();
+  });
+});
+
+describe('closing the grid', () => {
+  it('never reopens the split it replaced', () => {
+    const app = makeGridApp(IDS);
+    openSplit(app);
+    app.toggleTileGrid();
+    app.closeTileGrid({ reselect: false });
+    expect(app._splitPane).toBeNull();
+    expect(app._tilesOwnTerminal()).toBe(false);
+  });
+});