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/WorkspaceRowMenu.tsx

@@ -1,7 +1,10 @@
 /**
  * @file WorkspaceRowMenu — the sidebar workspace row's context menu, opened at
  * the pointer (right-click) or under the row's `⋯` button. Every item is an
- * existing call: Start/Stop (`POST /api/lanes/:id/start` slot 0 / `stop`),
+ * existing call: Start (`POST /api/lanes/:id/start`, the free tab the server
+ * picks — then the session opens, `onAction("started", runId)`) / Stop
+ * (`stop`, every tab of the workspace — counted from `GET /api/run` when the
+ * menu opens, and confirmed: "Stop N sessions?"),
  * Rename (the row's inline field), New workspace here (the Add modal prefilled),
  * Copy path, and Reset/Remove through `DestructiveLaneModal` — Reset only on a
  * managed lane. The server's guards are the real ones; the menu only hides
@@ -10,11 +13,15 @@
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
-import { useState } from "react";
+import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { api } from "../../lib/api";
 import type { Lane } from "../../lib/types";
 import { ContextMenu, MenuItem, MenuSeparator } from "../ContextMenu";
+import { confirmDialog } from "../../lib/confirm";
+import { copyText } from "../../lib/clipboard";
+import { toast } from "../../lib/toast";
+import { startInFreeTab } from "./startSession";
 
 export type WorkspaceMenuAction = "rename" | "new-here" | "reset" | "remove" | "started";
 
@@ -29,37 +36,70 @@ export function WorkspaceRowMenu({
   x: number;
   y: number;
   onClose: () => void;
-  /** Items the tree itself carries out (rename field, modals, selection). */
-  onAction: (action: WorkspaceMenuAction) => void;
+  /** Items the tree itself carries out (rename field, modals, selection);
+   *  `started` comes with the run it opened. */
+  onAction: (action: WorkspaceMenuAction, runId?: string) => void;
 }) {
   const { t } = useTranslation("lanes");
-  const [error, setError] = useState<string | null>(null);
+  // Every live tab of the workspace — slot 0 alone undercounts a split.
+  const [liveCount, setLiveCount] = useState<number | null>(null);
+  useEffect(() => {
+    let alive = true;
+    api.run
+      .list()
+      .then(
+        (r) =>
+          alive &&
+          setLiveCount(
+            (r.items ?? []).filter((x) => x.laneId === lane.id && x.status === "running").length
+          )
+      )
+      .catch(() => undefined);
+    return () => {
+      alive = false;
+    };
+  }, [lane.id]);
+  const live = liveCount === null ? !!lane.run_id || lane.status === "running" : liveCount > 0;
 
-  const run = async (fn: () => Promise<unknown>, then?: WorkspaceMenuAction) => {
-    setError(null);
+  const stop = async () => {
+    onClose();
+    const n = liveCount ?? 1;
+    if (
+      !(await confirmDialog({
+        title: t("menu.stopTitle", { count: n }),
+        message: t("menu.stopBody"),
+        confirmLabel: t("menu.stop"),
+        destructive: true,
+      }))
+    )
+      return;
     try {
-      await fn();
-      if (then) onAction(then);
-      onClose();
+      await api.lanes.action(lane.id, "stop");
     } catch (err) {
-      setError(err instanceof Error ? err.message : String(err));
+      toast.error(err);
+    }
+  };
+  const start = async () => {
+    onClose();
+    try {
+      onAction("started", await startInFreeTab(lane.id, { prompt: "" }));
+    } catch (err) {
+      toast.error(err);
     }
   };
-  const live = !!lane.run_id || lane.status === "running";
   return (
     <ContextMenu x={x} y={y} onClose={onClose} testId={`workspace-row-menu-${lane.id}`}>
-      <MenuItem
-        onSelect={() =>
-          live
-            ? void run(() => api.lanes.action(lane.id, "stop"))
-            : void run(() => api.lanes.action(lane.id, "start", { slot: 0, prompt: "" }), "started")
-        }
-      >
+      <MenuItem onSelect={() => void (live ? stop() : start())}>
         {live ? t("menu.stop") : t("menu.start")}
       </MenuItem>
       <MenuItem onSelect={() => onAction("rename")}>{t("menu.rename")}</MenuItem>
       <MenuItem onSelect={() => onAction("new-here")}>{t("menu.newHere")}</MenuItem>
-      <MenuItem onSelect={() => void run(() => navigator.clipboard.writeText(lane.cwd))}>
+      <MenuItem
+        onSelect={() => {
+          onClose();
+          void copyText(lane.cwd);
+        }}
+      >
         {t("menu.copyPath")}
       </MenuItem>
       <MenuSeparator />
@@ -71,11 +111,6 @@ export function WorkspaceRowMenu({
       <MenuItem danger onSelect={() => onAction("remove")}>
         {t("menu.remove")}
       </MenuItem>
-      {error && (
-        <p role="alert" className="px-2 py-1 text-[11px] text-status-danger">
-          {error}
-        </p>
-      )}
     </ContextMenu>
   );
 }