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  (POST /api/users/:id/tmux-restart) or every idle outdated one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>

server/lib/member-tmux.js

@@ -0,0 +1,103 @@
+/**
+ * @file member-tmux.js
+ * @description Server mode, one Linux user per account (S3): each member's
+ * own tmux server as the Users page shows it — the version it runs next to
+ * the installed one (`TMUX_BIN`), how many sessions it holds and whether an
+ * agent of theirs is working — and an admin's restart of it. A tmux server
+ * keeps the version it started with until its last session closes, so after
+ * a tmux upgrade an old server lingers; `tmux-member` (install-system) keeps
+ * every call on it matched to its own binary, and this is how an admin moves
+ * a member onto the new version on purpose. A restart ends every pane of
+ * theirs (their Claude sessions resume from the workspace).
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const { execFileSync } = require("node:child_process");
+
+const { db } = require("../db");
+const linux = require("./linux-accounts");
+const tmux = require("./tmux");
+
+const err = (code, message) => Object.assign(new Error(message), { code });
+
+// The installed tmux's version (`3.8`), re-read at most once a minute.
+let installed = { at: 0, bin: null, version: null };
+function installedVersion() {
+  const bin = linux.serverConf()?.tmuxInstalled || null;
+  if (installed.bin === bin && Date.now() - installed.at < 60_000) return installed.version;
+  let version = null;
+  if (bin) {
+    try {
+      version =
+        String(execFileSync(bin, ["-V"], { encoding: "utf8", timeout: 3000, stdio: "pipe" }))
+          .trim()
+          .replace(/^tmux\s+/, "") || null;
+    } catch {
+      /* missing or broken: unknown */
+    }
+  }
+  installed = { at: Date.now(), bin, version };
+  return version;
+}
+
+/** How many of `userId`'s workspaces have an agent working right now. */
+function busyCount(userId) {
+  return db
+    .prepare("SELECT COUNT(*) AS n FROM lanes WHERE owner_id = ? AND status = 'running'")
+    .get(userId).n;
+}
+
+/** One user's row; null for an account with no Linux side. */
+function rowFor(user, installedV) {
+  const acct = linux.accountFor(user.username);
+  if (!acct) return null;
+  const info = tmux.memberServerInfo(acct);
+  return {
+    id: user.id,
+    username: user.username,
+    ...info,
+    busy: busyCount(user.id),
+    outdated: !!(info.running && info.version && installedV && info.version !== installedV),
+  };
+}
+
+/** `{available, installed, matched, users: [...]}` for the Users page. */
+function overview(users) {
+  if (!linux.s3Enabled()) return { available: false, users: [] };
+  const conf = linux.serverConf();
+  const v = installedVersion();
+  return {
+    available: true,
+    installed: v,
+    // Whether calls on an older server already use its own binary.
+    matched: conf?.bins?.tmux !== conf?.tmuxInstalled,
+    users: users.map((u) => rowFor(u, v)).filter(Boolean),
+  };
+}
+
+/**
+ * Restart `user`'s tmux server. `{restarted: false}` when none ran; throws
+ * ETMUXSTUCK (with the pid) when it would not stop — root has to kill it.
+ */
+function restart(user) {
+  const acct = linux.accountFor(user.username);
+  if (!acct) throw err("ENOS3", "this account has no Linux user (S3 is not installed)");
+  const before = tmux.memberServerInfo(acct);
+  if (!before.running) return { restarted: false, before };
+  try {
+    tmux.killMemberServer(acct);
+  } catch {
+    /* judged by what is left below */
+  }
+  const after = tmux.memberServerInfo(acct);
+  if (after.running) {
+    const pid = before.pid || after.pid;
+    throw err(
+      "ETMUXSTUCK",
+      `${user.username}'s tmux server did not stop — run \`sudo kill -9 ${pid || "<pid>"}\` on the server`
+    );
+  }
+  return { restarted: true, before };
+}
+
+module.exports = { overview, restart, installedVersion };