feat(workspace): no double resume, server-picked tabs, terminal a11y

- A resume of a session a live pane already holds is refused (409
  ESESSIONLIVE with error.run_id) and the client opens that pane, pasting
  any typed message there; catalog tools refuse resumeSessionId
  (EUNSUPPORTED) instead of silently starting fresh.
- POST /api/lanes/:id/start takes slot: "auto": the server picks the free
  tab under the lane lock (components/lanes/startSession.ts on the client,
  kept out of WorkspaceHome so the sidebar does not pull react-markdown
  into the main bundle).
- Unsaved whole-file edits are guarded on every exit (Back, another file,
  tab switch, close, lane/session change, beforeunload).
- Closing an AI tab asks first; hiding a pane has its own icon. Tabs and
  pane headers show the session name, a state dot, rename by double-click.
- Terminal: Ctrl+M toggles Tab-moves-focus (no keyboard trap), Cmd+F /
  Ctrl+Shift+F find bar, clickable links (noopener), a write-only OSC 52
  clipboard, a Reconnecting overlay, debounced resizes, optional screen
  reader mode. Alt+1-4 / Alt+\ / Alt+W focus, split and hide panes.
- Changes panel: draggable splitter, wrapping git bar, history paging,
  disarming discard/undo/abort, inline diff comments pasted only into a
  visible pane; drag MIME guard on sidebar rows; IME-safe Enter; Show
  more in the sidebar and Recents; idle dots readable with sr-only text.
- Adds @xterm/addon-clipboard, @xterm/addon-search, @xterm/addon-web-links.

client/src/components/lanes/SessionMenu.tsx

@@ -6,16 +6,18 @@
  * opens its conversation — never a resume), open a live one in a split,
  * rename / archive / unarchive when the list offers them, copy its id, open
  * its analysis page, and close its live tab (`DELETE /api/run/:id`, what the
- * tab's X does).
+ * tab's X does — after the same confirm for an AI tab, which may be mid-turn).
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
-import { useState } from "react";
 import { useTranslation } from "react-i18next";
 import { useNavigate } from "react-router-dom";
 import { api, type RunHandle } from "../../lib/api";
 import type { Session } from "../../lib/types";
 import { ContextMenu, MenuItem, MenuSeparator, type MenuPoint } from "../ContextMenu";
+import { confirmDialog } from "../../lib/confirm";
+import { copyText } from "../../lib/clipboard";
+import { toast } from "../../lib/toast";
 
 export function SessionMenu({
   laneId,
@@ -39,7 +41,6 @@ export function SessionMenu({
 }) {
   const { t } = useTranslation("lanes");
   const navigate = useNavigate();
-  const [error, setError] = useState<string | null>(null);
   const runUrl = run && `/workspace?lane=${laneId}&run=${encodeURIComponent(run.id)}`;
 
   const pick = (fn: () => unknown) => () => {
@@ -48,12 +49,21 @@ export function SessionMenu({
   };
   const closeTab = async () => {
     if (!run) return;
-    setError(null);
+    onClose();
+    if (
+      run.tool !== "shell" &&
+      !(await confirmDialog({
+        title: t("tabs.stopTitle", { name: session?.name || t("tree.newSession") }),
+        message: t("tabs.stopBody"),
+        confirmLabel: t("tabs.stopConfirm"),
+        destructive: true,
+      }))
+    )
+      return;
     try {
       await api.run.kill(run.id);
-      onClose();
     } catch (err) {
-      setError(err instanceof Error ? err.message : String(err));
+      toast.error(err);
     }
   };
 
@@ -79,7 +89,7 @@ export function SessionMenu({
           <MenuItem onSelect={pick(() => navigate(`/sessions/${session.id}`))}>
             {t("sessionMenu.details")}
           </MenuItem>
-          <MenuItem onSelect={pick(() => void navigator.clipboard.writeText(session.id))}>
+          <MenuItem onSelect={pick(() => void copyText(session.id))}>
             {t("sessionMenu.copyId")}
           </MenuItem>
         </>
@@ -92,11 +102,6 @@ export function SessionMenu({
           {t("tabs.close")}
         </MenuItem>
       )}
-      {error && (
-        <p role="alert" className="px-2 py-1 text-[11px] text-status-danger">
-          {error}
-        </p>
-      )}
     </ContextMenu>
   );
 }