feat(server-s3): a member's tmux follows tmux upgrades — tmux-member + Users → Members' tmux

A member's tmux server keeps the version it started with until their last
pane closes, but the dashboard asked it with TMUX_BIN, the newest tmux: a
3.8 client on a 3.6 server spun it at 100% CPU (three members needed a
manual kill on 2026-10-15).

- /opt/agenthub/libexec/tmux-member (install-system, in sudoers): runs a
  member's tmux call with the binary of THEIR running server
  (/proc/<pid>/exe, found from the socket in /proc/net/unix), else
  TMUX_BIN. It runs as the member and execs only a process they own.
  sudoArgv uses it once installed (linux-accounts readConf), TMUX_BIN
  until then.
- Users → Members' tmux (GET /api/users/tmux): each member server's version
  beside the installed one, sessions, agents working. An admin restarts one
  (POST /api/users/:id/tmux-restart) or every idle outdated one
  (POST /api/users/tmux-restart-idle), with their password again, audited
  per member; a server that will not stop answers 409 ETMUXSTUCK naming
  its pid for root.
- server-s3-system.test.js: `delete` is a provision action since Delete
  user, so the "unknown action" case now uses `purge`.

Operators: run `sudo agenthub server install-system` once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

client/src/pages/Users.tsx

@@ -9,7 +9,9 @@
  * an admin — add a user, and ONE Edit per row (`UserEditDialog`: profile,
  * role, active/disabled, password, owned workspaces, sign out everywhere, sent
  * as one change), and the Claude/Codex account pool every user's sessions run
- * on (`AccountPoolCard`). Every change asks for the admin's OWN password again (the
+ * on (`AccountPoolCard`), and (one Linux user per account) each member's own
+ * tmux server beside the installed version, restartable by an admin
+ * (`MemberTmuxCard`). Every change asks for the admin's OWN password again (the
  * server refuses without it); an analyst only reads. A row shows the display
  * name and email under the username when set.
  * Laid out like the other list pages: icon header, a row of totals
@@ -48,6 +50,7 @@ import { ConfirmModal } from "../components/ConfirmModal";
 import { StatCard } from "../components/StatCard";
 import { ROLE_BADGE, UserEditDialog } from "../components/users/UserEditDialog";
 import { AccountPoolCard } from "../components/users/AccountPoolCard";
+import { MemberTmuxCard } from "../components/users/MemberTmuxCard";
 import { TableRowSkeleton } from "../components/Skeleton";
 
 type Role = AuthUser["role"];
@@ -296,6 +299,7 @@ export function Users() {
       </div>
 
       <AccountPoolCard isAdmin={isAdmin} />
+      <MemberTmuxCard isAdmin={isAdmin} />
 
       <section className="card">
         <div className="flex items-center gap-2 px-5 py-4 border-b border-border">

client/src/pages/__tests__/Users.test.tsx

@@ -40,6 +40,8 @@ const users = vi.hoisted(() => ({
   setPassword: vi.fn(),
   assignWorkspace: vi.fn(),
   get: vi.fn(),
+  // No S3 here: the members' tmux card stays hidden.
+  tmux: vi.fn(async () => ({ available: false, users: [] })),
 }));
 
 vi.mock("../../lib/api", async (importOriginal) => {