fix(shell): copy terminal selections from xterm buffer

The shell was delegating Cmd/Ctrl+C to document.execCommand('copy'),
which copied the rendered DOM selection instead of xterm's logical
buffer text. Wrapped values like login URLs could pick up row
whitespace or line breaks and break when pasted.

Route keyboard copy through terminal.getSelection() and the shared
clipboard helper. Also intercept native copy events on the terminal
container so mouse selection and browser copy actions use the same
normalized terminal text.

Remove the copy listener during teardown to avoid leaking handlers
across terminal reinitialization.

src/components/shell/hooks/useShellTerminal.ts

@@ -11,6 +11,7 @@ import {
   TERMINAL_OPTIONS,
   TERMINAL_RESIZE_DELAY_MS,
 } from '../constants/constants';
+import { copyTextToClipboard } from '../../../utils/clipboard';
 import { isCodexLoginCommand } from '../utils/auth';
 import { sendSocketMessage } from '../utils/socket';
 import { ensureXtermFocusStyles } from '../utils/terminalStyles';
@@ -103,6 +104,37 @@ export function useShellTerminal({
 
     nextTerminal.open(terminalContainerRef.current);
 
+    const copyTerminalSelection = async () => {
+      const selection = nextTerminal.getSelection();
+      if (!selection) {
+        return false;
+      }
+
+      return copyTextToClipboard(selection);
+    };
+
+    const handleTerminalCopy = (event: ClipboardEvent) => {
+      if (!nextTerminal.hasSelection()) {
+        return;
+      }
+
+      const selection = nextTerminal.getSelection();
+      if (!selection) {
+        return;
+      }
+
+      event.preventDefault();
+
+      if (event.clipboardData) {
+        event.clipboardData.setData('text/plain', selection);
+        return;
+      }
+
+      void copyTextToClipboard(selection);
+    };
+
+    terminalContainerRef.current.addEventListener('copy', handleTerminalCopy);
+
     nextTerminal.attachCustomKeyEventHandler((event) => {
       const activeAuthUrl = isCodexLoginCommand(initialCommandRef.current)
         ? CODEX_DEVICE_AUTH_URL
@@ -132,7 +164,7 @@ export function useShellTerminal({
       ) {
         event.preventDefault();
         event.stopPropagation();
-        document.execCommand('copy');
+        void copyTerminalSelection();
         return false;
       }
 
@@ -211,6 +243,7 @@ export function useShellTerminal({
     resizeObserver.observe(terminalContainerRef.current);
 
     return () => {
+      terminalContainerRef.current?.removeEventListener('copy', handleTerminalCopy);
       resizeObserver.disconnect();
       if (resizeTimeoutRef.current !== null) {
         window.clearTimeout(resizeTimeoutRef.current);