feat: v2.6.0 — Chat UI composer (+ menu, project files, activity panel, permission mode, Stop), git on a workspace's extra folders (#70), long paste as a file (#68), S3 server mode (experimental)

Chat UI:
- Each Claude/Codex session keeps its own chat/terminal view; Settings only
  sets how new sessions open.
- Composer + menu: upload, project files and folders (#54, also dragged from
  the Files/Changes tree), context files, recent uploads, skills, plugins.
- Activity side panel (progress, outputs, files read, uploads, memory,
  skills, connectors) with a file preview; edited-file counts per turn.
- Permission-mode chip (Shift+Tab steps, read back from the pane:
  server/lib/pane-mode.js, GET|POST /api/run/:id/permission-mode).
- Stop (Esc) while the main agent works; the status is checked per agent
  (with session_id /api/agents ignores its status filter) and re-read every
  5 s while Stop shows.
- Dropped images shown in the conversation (GET /api/run/drop/:name, the
  requester's own drop dir), full-size viewer.
- A plain-text paste over 5,000 characters is attached as pasted-text.txt,
  so no prompt reaches tmux/argv limits (#68).

Changes panel: every /api/lanes/:id/git* route takes ?source=<lane_sources
id> (sourceFolder; ENOSOURCE otherwise) and a folder picker switches the
whole panel to a workspace's extra folder (#70).

Server mode S3 (one Linux user per account) — experimental, verified with
fake sudo plus a P6 managed-settings spike on a test account:
- member tmux listing runs in the background (cached, 15 s => unknown);
- transcript snapshot copy is async, chunked, temp file + rename;
- Express Layer patch only on Express 4;
- tmux capturePane/sendKey go to the member's own server.

Docs: the multi-user design moved in as docs/plans/server-mode/README.md
(the AgentHub-Server repo is gone); S3-PLAN P6 result; LANES/API/openapi.

client/src/components/run/PaneGrid.tsx

@@ -29,6 +29,7 @@ import {
   ChevronDown,
   Columns2,
   GripVertical,
+  MessageSquare,
   Minimize2,
   Rows2,
   SquareTerminal,
@@ -55,6 +56,7 @@ import {
 } from "../../lib/paneLayout";
 import { AiToolIcon } from "../AiToolIcon";
 import { RunDot, type RunState } from "./ConsoleTabs";
+import { setSessionChat, useSessionChat } from "../../lib/chatUi";
 
 export const PANE_DRAG_TYPE = "application/x-agenthub-pane";
 /** The slot being dragged: `dataTransfer` data cannot be read during dragover. */
@@ -191,9 +193,37 @@ function PaneMenu({
 const ITEM =
   "flex w-full items-center gap-2.5 rounded-md px-2.5 py-1.5 text-left text-sm text-fg-secondary hover:bg-surface-4 hover:text-fg-primary";
 
-/** A pane's split-right / split-down menus: move a hidden run beside
- *  `slot`, or start a new terminal or AI tool there. In a pane header when the view is
- *  split, beside Tools in the tab bar while one pane is shown. */
+/** Chat UI ⇄ terminal for a Claude/Codex pane — this session's own view
+ *  (`lib/chatUi.ts`); a session with no id yet has no chat to show. */
+function ChatToggle({ run }: { run?: RunHandle }) {
+  const { t } = useTranslation("lanes");
+  const chat = useSessionChat(run?.sessionId);
+  if (!run?.sessionId || (run.tool !== "claude" && run.tool !== "codex")) return null;
+  const sessionId = run.sessionId;
+  const label = chat ? t("panes.showTerminal") : t("panes.showChat");
+  return (
+    <button
+      type="button"
+      data-testid={`pane-chat-toggle-${run.slot ?? 0}`}
+      aria-pressed={chat}
+      title={label}
+      aria-label={label}
+      onClick={() => setSessionChat(sessionId, !chat)}
+      className="flex h-6 w-6 items-center justify-center rounded text-fg-muted hover:bg-surface-4 hover:text-fg-primary"
+    >
+      {chat ? (
+        <SquareTerminal className="h-3.5 w-3.5" />
+      ) : (
+        <MessageSquare className="h-3.5 w-3.5" />
+      )}
+    </button>
+  );
+}
+
+/** A pane's chat/terminal toggle and split-right / split-down menus: move a
+ *  hidden run beside `slot`, or start a new terminal or AI tool there. In a
+ *  pane header when the view is split, beside Tools in the tab bar while one
+ *  pane is shown. */
 export function SplitMenus({
   slot,
   shown,
@@ -222,6 +252,7 @@ export function SplitMenus({
   const full = shown.length >= MAX_PANES;
   return (
     <>
+      <ChatToggle run={runs.find((x) => (x.slot ?? 0) === slot)} />
       {(["right", "bottom"] as const).map((edge) => (
         <PaneMenu
           key={edge}
@@ -446,6 +477,8 @@ export function PaneGrid({
             key={slot}
             data-testid={`pane-${slot}`}
             data-focused={r && focused ? "true" : undefined}
+            // A menu opened in this pane stays inside it (`menuRoom`).
+            data-menu-bounds
             className={r ? "absolute flex flex-col" : "hidden"}
             style={r ? pct(r) : undefined}
             onPointerDownCapture={() => r && focus(slot)}