diff --git a/apps/next/src/components/agent-workspace/xterm-session.tsx b/apps/next/src/components/agent-workspace/xterm-session.tsx
index 2730587..13b26a6 100644
--- a/apps/next/src/components/agent-workspace/xterm-session.tsx
+++ b/apps/next/src/components/agent-workspace/xterm-session.tsx
@@ -13,6 +13,21 @@ import '@xterm/xterm/css/xterm.css';
 const TERMINAL_FONT =
   "var(--font-victor-mono), 'Symbols Nerd Font Mono', 'Geist Mono', ui-monospace, monospace";
 
+// Persisted user preference for copy-on-select. A stored value takes precedence
+// over the `copyOnSelect` prop default so the toggle sticks across sessions.
+const COPY_ON_SELECT_KEY = 'spoon.terminal.copyOnSelect';
+
+const readStoredCopyOnSelect = (): boolean | undefined => {
+  try {
+    const stored = window.localStorage.getItem(COPY_ON_SELECT_KEY);
+    if (stored === 'true') return true;
+    if (stored === 'false') return false;
+  } catch {
+    // localStorage may be unavailable (private mode, SSR); fall back to prop.
+  }
+  return undefined;
+};
+
 export type XtermStatus =
   | 'idle'
   | 'connecting'
@@ -95,6 +110,29 @@ export const XtermSession = ({
   const [status, setStatus] = useState<XtermStatus>('idle');
   const [errorText, setErrorText] = useState<string>();
   const [reconnectKey, setReconnectKey] = useState(0);
+  // localStorage overrides the prop default; the prop is only the initial value
+  // when nothing has been persisted yet.
+  const [copyEnabled, setCopyEnabled] = useState<boolean>(
+    () => readStoredCopyOnSelect() ?? copyOnSelect ?? false,
+  );
+  // The connect effect registers onSelectionChange once; it reads the current
+  // toggle through this ref so live flips take effect without a reconnect.
+  const copyEnabledRef = useRef(copyEnabled);
+  useEffect(() => {
+    copyEnabledRef.current = copyEnabled;
+  }, [copyEnabled]);
+
+  const toggleCopyOnSelect = () => {
+    setCopyEnabled((prev) => {
+      const next = !prev;
+      try {
+        window.localStorage.setItem(COPY_ON_SELECT_KEY, String(next));
+      } catch {
+        // Persistence is best-effort; ignore storage failures.
+      }
+      return next;
+    });
+  };
 
   // Update the live terminal's theme without tearing down the session.
   useEffect(() => {
@@ -164,13 +202,22 @@ export const XtermSession = ({
       termRef.current = term;
       fitRef.current = fit;
 
-      // Task 11 will wire clipboard copy-on-select behavior here. Accept the
-      // prop now so callers (and the effect deps) are stable across that change.
-      if (copyOnSelect) {
-        term.onSelectionChange(() => {
-          // no-op placeholder until Task 11
-        });
-      }
+      // Copy-on-select: when enabled, mirror the selection to the clipboard.
+      // Registered once; the ref lets live toggle flips apply without a
+      // reconnect. Clipboard access is guarded — it may be unavailable or
+      // denied, and empty selections are skipped.
+      term.onSelectionChange(() => {
+        if (!copyEnabledRef.current) return;
+        const selection = term.getSelection();
+        if (!selection) return;
+        try {
+          void navigator.clipboard.writeText(selection).catch(() => {
+            // clipboard write denied/unavailable; ignore
+          });
+        } catch {
+          // navigator.clipboard missing entirely; ignore
+        }
+      });
 
       const sendResize = () => {
         if (ws?.readyState !== WebSocket.OPEN) return;
@@ -285,16 +332,27 @@ export const XtermSession = ({
                     ? 'Terminal not configured'
                     : 'Connection error'}
         </p>
-        {status === 'closed' || status === 'error' ? (
-          <Button
-            type='button'
-            variant='outline'
-            size='sm'
-            onClick={() => setReconnectKey((key) => key + 1)}
-          >
-            Reconnect
-          </Button>
-        ) : null}
+        <div className='flex items-center gap-3'>
+          <label className='text-muted-foreground flex cursor-pointer items-center gap-1.5 text-xs select-none'>
+            <input
+              type='checkbox'
+              className='accent-primary size-3.5'
+              checked={copyEnabled}
+              onChange={toggleCopyOnSelect}
+            />
+            Copy on select
+          </label>
+          {status === 'closed' || status === 'error' ? (
+            <Button
+              type='button'
+              variant='outline'
+              size='sm'
+              onClick={() => setReconnectKey((key) => key + 1)}
+            >
+              Reconnect
+            </Button>
+          ) : null}
+        </div>
       </div>
       {status === 'unconfigured' ? (
         <div className='text-muted-foreground flex flex-1 items-center justify-center p-6 text-center text-sm'>
diff --git a/apps/next/tests/component/xterm-session.test.tsx b/apps/next/tests/component/xterm-session.test.tsx
index 095389c..963e0f7 100644
--- a/apps/next/tests/component/xterm-session.test.tsx
+++ b/apps/next/tests/component/xterm-session.test.tsx
@@ -1,9 +1,17 @@
-import { render, screen, waitFor } from '@testing-library/react';
+import { cleanup, fireEvent, render, screen, waitFor } from '@testing-library/react';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { XtermSession } from '../../src/components/agent-workspace/xterm-session';
 
-const { openSpy, wsInstances, fetchSpy, fitSpy } = vi.hoisted(() => ({
+const {
+  openSpy,
+  wsInstances,
+  fetchSpy,
+  fitSpy,
+  selectionHandlers,
+  getSelectionSpy,
+  writeTextSpy,
+} = vi.hoisted(() => ({
   openSpy: vi.fn(),
   wsInstances: [] as Array<{
     url: string;
@@ -12,6 +20,11 @@ const { openSpy, wsInstances, fetchSpy, fitSpy } = vi.hoisted(() => ({
   }>,
   fetchSpy: vi.fn(),
   fitSpy: vi.fn(),
+  selectionHandlers: [] as (() => void)[],
+  getSelectionSpy: vi.fn<() => string>(() => ''),
+  writeTextSpy: vi.fn<(text: string) => Promise<void>>(() =>
+    Promise.resolve(),
+  ),
 }));
 
 class FakeTerminal {
@@ -22,7 +35,10 @@ class FakeTerminal {
   loadAddon = vi.fn();
   onData = vi.fn();
   onResize = vi.fn();
-  onSelectionChange = vi.fn();
+  onSelectionChange = vi.fn((cb: () => void) => {
+    selectionHandlers.push(cb);
+  });
+  getSelection = getSelectionSpy;
   dispose = vi.fn();
   refresh = vi.fn();
   write = vi.fn();
@@ -64,8 +80,32 @@ class FakeWebSocket {
 
 beforeEach(() => {
   wsInstances.length = 0;
+  selectionHandlers.length = 0;
   openSpy.mockClear();
   fitSpy.mockClear();
+  getSelectionSpy.mockReset();
+  getSelectionSpy.mockReturnValue('');
+  writeTextSpy.mockReset();
+  writeTextSpy.mockResolvedValue(undefined);
+  const store = new Map<string, string>();
+  const localStorageMock = {
+    getItem: (key: string) => (store.has(key) ? store.get(key)! : null),
+    setItem: (key: string, value: string) => store.set(key, String(value)),
+    removeItem: (key: string) => store.delete(key),
+    clear: () => store.clear(),
+    key: (index: number) => Array.from(store.keys())[index] ?? null,
+    get length() {
+      return store.size;
+    },
+  };
+  Object.defineProperty(window, 'localStorage', {
+    configurable: true,
+    value: localStorageMock,
+  });
+  Object.defineProperty(navigator, 'clipboard', {
+    configurable: true,
+    value: { writeText: writeTextSpy },
+  });
   fetchSpy.mockReset();
   fetchSpy.mockResolvedValue({
     ok: true,
@@ -93,6 +133,7 @@ beforeEach(() => {
 });
 
 afterEach(() => {
+  cleanup();
   vi.unstubAllGlobals();
 });
 
@@ -193,4 +234,133 @@ describe('XtermSession', () => {
     expect(ws.close).not.toHaveBeenCalled();
     expect(wsInstances).toHaveLength(1);
   });
+
+  it('copies the selection to the clipboard when copy-on-select is enabled', async () => {
+    render(
+      <XtermSession
+        active
+        copyOnSelect
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(selectionHandlers.length).toBeGreaterThan(0));
+    getSelectionSpy.mockReturnValue('hello world');
+    selectionHandlers.forEach((cb) => cb());
+
+    await waitFor(() =>
+      expect(writeTextSpy).toHaveBeenCalledWith('hello world'),
+    );
+  });
+
+  it('does not copy when copy-on-select is disabled', async () => {
+    render(
+      <XtermSession active tokenUrl='/api/box/terminal-token' sessionKey='box-1' />,
+    );
+
+    await waitFor(() => expect(selectionHandlers.length).toBeGreaterThan(0));
+    getSelectionSpy.mockReturnValue('should not copy');
+    selectionHandlers.forEach((cb) => cb());
+    await Promise.resolve();
+
+    expect(writeTextSpy).not.toHaveBeenCalled();
+  });
+
+  it('skips empty selections even when enabled', async () => {
+    render(
+      <XtermSession
+        active
+        copyOnSelect
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(selectionHandlers.length).toBeGreaterThan(0));
+    getSelectionSpy.mockReturnValue('');
+    selectionHandlers.forEach((cb) => cb());
+    await Promise.resolve();
+
+    expect(writeTextSpy).not.toHaveBeenCalled();
+  });
+
+  it('swallows clipboard errors without crashing', async () => {
+    writeTextSpy.mockRejectedValue(new Error('denied'));
+    render(
+      <XtermSession
+        active
+        copyOnSelect
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(selectionHandlers.length).toBeGreaterThan(0));
+    getSelectionSpy.mockReturnValue('boom');
+    selectionHandlers.forEach((cb) => cb());
+
+    await waitFor(() => expect(writeTextSpy).toHaveBeenCalledWith('boom'));
+    // Rejection is caught; the component stays mounted.
+    expect(screen.getByRole('checkbox')).toBeInTheDocument();
+  });
+
+  it('renders the header toggle and persists flips to localStorage', async () => {
+    render(
+      <XtermSession active tokenUrl='/api/box/terminal-token' sessionKey='box-1' />,
+    );
+
+    await waitFor(() => expect(selectionHandlers.length).toBeGreaterThan(0));
+    const checkbox = screen.getByRole('checkbox');
+    expect(checkbox).not.toBeChecked();
+
+    // Off: a selection is not copied.
+    getSelectionSpy.mockReturnValue('nope');
+    selectionHandlers.forEach((cb) => cb());
+    await Promise.resolve();
+    expect(writeTextSpy).not.toHaveBeenCalled();
+
+    // Flip on: persists and now copies.
+    fireEvent.click(checkbox);
+    expect(checkbox).toBeChecked();
+    expect(
+      window.localStorage.getItem('spoon.terminal.copyOnSelect'),
+    ).toBe('true');
+
+    getSelectionSpy.mockReturnValue('now copied');
+    selectionHandlers.forEach((cb) => cb());
+    await waitFor(() =>
+      expect(writeTextSpy).toHaveBeenCalledWith('now copied'),
+    );
+
+    // Flip off again: persists false.
+    fireEvent.click(checkbox);
+    expect(checkbox).not.toBeChecked();
+    expect(
+      window.localStorage.getItem('spoon.terminal.copyOnSelect'),
+    ).toBe('false');
+  });
+
+  it('lets the persisted localStorage value override the prop default', () => {
+    window.localStorage.setItem('spoon.terminal.copyOnSelect', 'true');
+    render(
+      <XtermSession active tokenUrl='/api/box/terminal-token' sessionKey='box-1' />,
+    );
+
+    const checkbox = screen.getByRole('checkbox');
+    expect(checkbox).toBeChecked();
+
+    window.localStorage.setItem('spoon.terminal.copyOnSelect', 'false');
+    render(
+      <XtermSession
+        active
+        copyOnSelect
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-2'
+      />,
+    );
+    // The second instance's checkbox reads the persisted false over prop=true.
+    const checkboxes = screen.getAllByRole('checkbox');
+    expect(checkboxes[checkboxes.length - 1]).not.toBeChecked();
+  });
 });