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/WorkspaceRow.tsx

@@ -6,7 +6,9 @@
  * session there) and `⋯` (the row menu, `WorkspaceRowMenu.tsx`, also on
  * right-click). Dragging it, or Alt+↑/↓, reorders the list — a viewer
  * preference kept in localStorage (`laneOrderStorage.ts`), never written to
- * the lane row.
+ * the lane row. Only a workspace row's own drag (`LANE_DRAG_TYPE`) is taken —
+ * a file, a tab or a text dragged over is not a reorder. F2 renames too; the
+ * dot's meaning is screen-reader text, and an idle dot is a ring.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -14,6 +16,12 @@ import { useState, type MouseEvent } from "react";
 import { useTranslation } from "react-i18next";
 import { ChevronDown, ChevronRight, MoreHorizontal, Plus } from "lucide-react";
 import type { Lane } from "../../lib/types";
+import { isSubmitEnter } from "../../lib/keys";
+
+/** What a workspace row's drag carries: its index in the list. */
+export const LANE_DRAG_TYPE = "application/x-agenthub-lane";
+const isLaneDrag = (e: { dataTransfer: DataTransfer | null }) =>
+  !!e.dataTransfer?.types?.includes(LANE_DRAG_TYPE);
 
 /** The row's dot: the lane's liveness, plus a running pulse and needs-you. */
 export function workspaceDot(lane: Lane): string {
@@ -21,7 +29,17 @@ export function workspaceDot(lane: Lane): string {
   if (lane.liveness === "dead" || lane.status === "error") return "bg-status-danger";
   if (lane.status === "running") return "bg-status-success animate-pulse-slow";
   if (lane.liveness === "active") return "bg-status-success";
-  return "bg-surface-4";
+  // A ring, not a fill: an idle surface-4 dot vanished on the light themes.
+  return "border border-fg-muted";
+}
+
+/** What the dot means (`row.state.*`), for a screen reader. */
+export function workspaceDotLabel(lane: Lane): string {
+  if (lane.needs_action) return "needsYou";
+  if (lane.liveness === "dead" || lane.status === "error") return "error";
+  if (lane.status === "running") return "running";
+  if (lane.liveness === "active") return "active";
+  return "idle";
 }
 
 export function workspaceName(lane: Lane): string {
@@ -78,19 +96,23 @@ export function WorkspaceRow({
       draggable={!renaming}
       onDragStart={(e) => {
         // Firefox starts no drag at all without a setData call.
-        e.dataTransfer.setData("text/plain", String(index));
+        e.dataTransfer.setData(LANE_DRAG_TYPE, String(index));
         e.dataTransfer.effectAllowed = "move";
       }}
       onDragOver={(e) => {
+        if (!isLaneDrag(e)) return;
         e.preventDefault();
         setDropTarget(true);
       }}
       onDragLeave={() => setDropTarget(false)}
       onDragEnd={() => setDropTarget(false)}
       onDrop={(e) => {
-        e.preventDefault();
         setDropTarget(false);
-        const from = Number(e.dataTransfer.getData("text/plain"));
+        if (!isLaneDrag(e)) return;
+        e.preventDefault();
+        const raw = e.dataTransfer.getData(LANE_DRAG_TYPE);
+        // Number("") is 0: an empty payload must not move the first row.
+        const from = raw === "" ? NaN : Number(raw);
         if (Number.isInteger(from)) onReorder(from, index);
       }}
       onContextMenu={openMenu}
@@ -125,7 +147,7 @@ export function WorkspaceRow({
           // Blur CANCELS — Enter is the only save, so one edit fires one PATCH.
           onBlur={() => onRenameEnd(null)}
           onKeyDown={(e) => {
-            if (e.key === "Enter") onRenameEnd(draft.trim());
+            if (isSubmitEnter(e)) onRenameEnd(draft.trim());
             if (e.key === "Escape") onRenameEnd(null);
           }}
           className="my-1 min-w-0 flex-1 rounded border border-accent bg-surface-1 px-1.5 py-0.5 text-[13px] text-fg-primary"
@@ -135,12 +157,19 @@ export function WorkspaceRow({
           type="button"
           data-testid={`workspace-open-${lane.id}`}
           aria-current={selected ? "true" : undefined}
-          onClick={onSelect}
+          // A double-click's second click renames instead of opening again.
+          onClick={(e) => e.detail < 2 && onSelect()}
           onDoubleClick={() => {
             setDraft(lane.title || "");
             onRenameStart();
           }}
           onKeyDown={(e) => {
+            if (e.key === "F2") {
+              e.preventDefault();
+              setDraft(lane.title || "");
+              onRenameStart();
+              return;
+            }
             if (!e.altKey || (e.key !== "ArrowUp" && e.key !== "ArrowDown")) return;
             e.preventDefault();
             onReorder(index, index + (e.key === "ArrowUp" ? -1 : 1));
@@ -148,7 +177,8 @@ export function WorkspaceRow({
           title={`${lane.cwd}\n${t("row.hint")}`}
           className="flex min-w-0 flex-1 items-center gap-2 py-1.5 text-left"
         >
-          <span className={`h-2 w-2 shrink-0 rounded-full ${workspaceDot(lane)}`} />
+          <span aria-hidden className={`h-2 w-2 shrink-0 rounded-full ${workspaceDot(lane)}`} />
+          <span className="sr-only">{t(`row.state.${workspaceDotLabel(lane)}`)}</span>
           <span className="truncate text-[13px] text-fg-primary">{name}</span>
         </button>
       )}