fix(terminal): psmux wheel scrolling, per-platform tmux upgrade advice, Windows-safe server tests

- Server tests on Windows no longer reach the user's real psmux: psmux
  ignores TMUX_TMPDIR (and 3.3.x PSMUX_DATA_DIR), so quit.test.js's Quit and
  the runner's kill-server ended every live lane pane — the pre-commit hook
  included. scripts/test-server.js now takes tmux off the suites' PATH there.
- Wheel scrolling on Windows: psmux never turns mouse tracking on for its
  client, so xterm.js never reported the wheel and a pane could not scroll.
  A Windows attach is told {type:"wheel"} and the browser sends the SGR wheel
  report itself; psmux scrolls or forwards it to the pane's app.
- tmux.upgradeAdvice(): the oldest tmux AgentHub asks for and how each
  platform upgrades (psmux 3.4.0 -> winget upgrade marlocarlo.psmux; tmux 3.7
  -> brew upgrade tmux / build the release on Linux). Used by the doctor,
  GET /api/run/tmux ({available, version, upgrade}), `agenthub doctor`, and a
  sticky toast on the Workspace page. Advice only: nothing installs tmux.

Committed with --no-verify (user's call): the pre-commit hook runs the full
backend suite, which has ~378 pre-existing failures on Windows (S3/Linux-only
tests: sudo, /proc, systemd, members). Every test touching this change passes:
pty-attach, tmux, run, plugin-doctor-tmux, TerminalView, Workspace, and the
client tests related to the changed files; tsc and the header audit are clean.

bin/agenthub.js

@@ -1284,12 +1284,14 @@ async function cmdDoctor() {
   // warning, not a failure: it costs the run console and `lanes shell`, nothing
   // else.
   try {
-    const { available } = await get("/api/run/tmux");
+    const { available, upgrade } = await get("/api/run/tmux");
     console.log(
-      available
+      !available
-        ? `${c.green("✔")}  tmux  available to the server`
+        ? `${c.yellow("!")}  tmux  not on the server's PATH — Start Run and \`agenthub workspace shell\` will fail. ` +
-        : `${c.yellow("!")}  tmux  not on the server's PATH — Start Run and \`agenthub workspace shell\` will fail. ` +
             `Install it (sudo apt install tmux / brew install tmux), then restart the server`
+        : upgrade
+          ? `${c.yellow("!")}  tmux  ${upgrade}`
+          : `${c.green("✔")}  tmux  available to the server`
     );
   } catch {
     console.log(`${c.dim("·")}  tmux  not reported by this server`);

client/src/components/run/TerminalView.tsx

@@ -355,9 +355,20 @@ export const TerminalView = memo(function TerminalView({
       // `false` also blocks tmux's own wheel scrolling. `x10` counts as off here
       // because that protocol reports button presses only, never the wheel — so
       // xterm takes the emulation path for it as well.
-      term.attachCustomWheelEventHandler(() => {
+      // psmux (Windows) never turns tracking on, so xterm never reports the
+      // wheel there; on the server's `{type:"wheel"}` this pane sends the SGR
+      // wheel report itself — psmux scrolls, or hands it to the pane's app.
+      // ponytail: at 1;1, which is all psmux reports to the app anyway.
+      let ownWheel = false;
+      term.attachCustomWheelEventHandler((ev) => {
         const mode = term.modes.mouseTrackingMode;
         const tracked = mode !== "none" && mode !== "x10";
+        if (!tracked && ownWheel) {
+          if (ev.deltaY && wsRef.current?.readyState === WebSocket.OPEN) {
+            wsRef.current.send(`\x1b[<${ev.deltaY < 0 ? 64 : 65};1;1M`);
+          }
+          return false;
+        }
         return tracked || term.buffer.active.type !== "alternate";
       });
 
@@ -530,6 +541,8 @@ export const TerminalView = memo(function TerminalView({
                   requestAnimationFrame(scaleToFit);
                 } else if (msg.type === "lead") {
                   takeLead();
+                } else if (msg.type === "wheel") {
+                  ownWheel = true;
                 } else if (msg.type === "exit") {
                   ended = true;
                   term.write(`\r\n${tRef.current("terminal.ended", { code: msg.code })}\r\n`);

client/src/components/run/__tests__/TerminalView.test.tsx

@@ -231,6 +231,24 @@ describe("TerminalView", () => {
     expect(wheelHandlerMock.mock.calls[0]![0]!(new Event("wheel"))).toBe(false);
   });
 
+  it("sends the wheel itself once the server says its tmux never tracks the mouse", () => {
+    // psmux (Windows) never turns mouse tracking on for its client, so xterm
+    // never reports the wheel and the pane could not be scrolled at all.
+    termState.modes.mouseTrackingMode = "none";
+    termState.buffer.active.type = "alternate";
+    render(<TerminalView runId="agenthub-lane-1" wsBaseUrl="ws://localhost:4820" />);
+    const ws = MockWebSocket.instances[MockWebSocket.instances.length - 1]!;
+    ws.onmessage?.({ data: '{"type":"wheel"}' });
+    const wheel = wheelHandlerMock.mock.calls[wheelHandlerMock.mock.calls.length - 1]![0]!;
+    expect(wheel(new WheelEvent("wheel", { deltaY: -100 }))).toBe(false);
+    expect(wheel(new WheelEvent("wheel", { deltaY: 100 }))).toBe(false);
+    expect(ws.sent).toEqual(["\x1b[<64;1;1M", "\x1b[<65;1;1M"]);
+    // Tracked again (a tmux that does report): xterm sends it, never twice.
+    termState.modes.mouseTrackingMode = "any";
+    expect(wheel(new WheelEvent("wheel", { deltaY: -100 }))).toBe(true);
+    expect(ws.sent).toHaveLength(2);
+  });
+
   it("keeps Shift+Tab in the terminal instead of letting focus escape", () => {
     render(<TerminalView runId="agenthub-lane-1" wsBaseUrl="ws://localhost:4820" />);
     const handler = keyHandlerMock.mock.calls[0]![0]! as (e: KeyboardEvent) => boolean;

client/src/i18n/locales/en/lanes.json

@@ -617,5 +617,6 @@
   "fx.readOnlyHome": "Another user's home — view and download only",
   "fx.readOnly": "Read-only",
   "fx.readOnlyHint": "This is another user's home: you can view, copy and download, not change it.",
-  "fx.homeEmpty": "Nothing in your home yet — its hidden files (.bashrc, .claude…) are not shown here. Your workspaces are on the left."
+  "fx.homeEmpty": "Nothing in your home yet — its hidden files (.bashrc, .claude…) are not shown here. Your workspaces are on the left.",
+  "tmuxUpgrade": "Upgrade tmux: {{advice}}"
 }

client/src/i18n/locales/vi/lanes.json

@@ -617,5 +617,6 @@
   "fx.readOnlyHome": "Home của user khác — chỉ xem và tải về",
   "fx.readOnly": "Chỉ đọc",
   "fx.readOnlyHint": "Đây là home của user khác: bạn chỉ xem, sao chép và tải về được, không sửa được.",
-  "fx.homeEmpty": "Home của bạn chưa có thư mục nào — các file ẩn (.bashrc, .claude…) không hiện ở đây. Các workspace nằm ở danh sách bên trái."
+  "fx.homeEmpty": "Home của bạn chưa có thư mục nào — các file ẩn (.bashrc, .claude…) không hiện ở đây. Các workspace nằm ở danh sách bên trái.",
+  "tmuxUpgrade": "Cần nâng cấp tmux: {{advice}}"
 }

client/src/lib/api.ts

@@ -2936,8 +2936,12 @@ export const api = {
     /** GET /api/run/binary - whether the lane tool's CLI was found on PATH (fresh look). */
     binary: (tool: LaneTool = "claude") =>
       request<{ found: boolean; path: string | null }>(`/run/binary?tool=${tool}`),
-    /** GET /api/run/tmux - whether the `tmux` binary was found on PATH. */
+    /** GET /api/run/tmux - whether the `tmux` binary was found on PATH, its
-    tmuxAvailable: () => request<{ available: boolean }>("/run/tmux"),
+     *  version, and this platform's upgrade advice when it is too old. */
+    tmuxAvailable: () =>
+      request<{ available: boolean; version?: string | null; upgrade?: string | null }>(
+        "/run/tmux"
+      ),
     /** GET /api/run/cwds - suggested working directories for the cwd picker. */
     cwds: () => request<{ items: CwdSuggestion[] }>("/run/cwds"),
     /** GET /api/run/files - path-completion suggestions under `cwd`; `dirs`

client/src/pages/Workspace.tsx

@@ -665,6 +665,25 @@ export function Workspace() {
   const { local } = usePermissions();
   const [searchParams, setSearchParams] = useSearchParams();
 
+  // The server's tmux is older than this platform needs (psmux < 3.4.0 on
+  // Windows, tmux < 3.7 elsewhere): say how to upgrade it, until it is.
+  // Sticky (an error toast) so the command can be copied. An older server or
+  // no answer says nothing.
+  useEffect(() => {
+    let live = true;
+    (async () => {
+      try {
+        const { upgrade } = await api.run.tmuxAvailable();
+        if (live && upgrade) toast.error(tLanes("tmuxUpgrade", { advice: upgrade }));
+      } catch {
+        /* nothing to say */
+      }
+    })();
+    return () => {
+      live = false;
+    };
+  }, [tLanes]);
+
   // Lane state: the list is the shared store the sidebar reads too; the
   // selection is the URL's `?lane=` (the sidebar sets it, so does a
   // notification click), falling back to the last one shown, then the first.

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

@@ -459,6 +459,23 @@ describe("Workspace page — lane integration", () => {
 });
 
 describe("Workspace layout", () => {
+  it("asks the user to upgrade a tmux older than their platform needs", async () => {
+    const { toast } = await import("../../lib/toast");
+    const shown = vi.spyOn(toast, "error");
+    const run = api.run as unknown as Record<string, unknown>;
+    run.tmuxAvailable = vi.fn().mockResolvedValue({
+      available: true,
+      version: "3.3.2",
+      upgrade: "psmux 3.3.2 is older than 3.4.0 — winget upgrade marlocarlo.psmux",
+    });
+    onTestFinished(() => {
+      delete run.tmuxAvailable;
+      shown.mockRestore();
+    });
+    await renderWorkspace();
+    expect(shown).toHaveBeenCalledWith(expect.stringContaining("winget upgrade marlocarlo.psmux"));
+  });
+
   it("shows no empty banner when there is no workspace (the sidebar's + adds one)", async () => {
     lanesToReturn = [];
     await renderWorkspace();

docs/API.md

@@ -2792,7 +2792,7 @@ The `/api/run/*` namespace starts and manages `claude` subprocesses in tmux-back
 
 ```http
 GET    /api/run                       List all live runs (computed fresh from tmux state)
-GET    /api/run/tmux                  { available: bool } — whether tmux is on PATH
+GET    /api/run/tmux                  { available: bool, version, upgrade } — whether tmux is on PATH, its version, and this platform's upgrade advice when it is older than AgentHub asks for (psmux 3.4.0 on Windows → `winget upgrade marlocarlo.psmux`; tmux 3.7 on macOS → `brew upgrade tmux`, on Linux → build the release), else null; the Workspace shows it as a sticky toast
 GET    /api/run/binary?tool=          { found, path } for the `claude`, `codex` or `agy` binary
 GET    /api/run/cwds                  Suggested cwds (dashboard, home, recent)
 GET    /api/run/history?limit=&laneId=&tool=  Persisted run history; laneId narrows to one lane's runs, tool (with laneId) to one tool's — `shell` = Terminal tabs
@@ -3209,7 +3209,7 @@ Sent when a notification is created.
 
 #### /ws-pty/:runId — PTY frames
 
-A dedicated binary WebSocket stream (not JSON-framed) for tmux-backed PTY transport. Established by the Workspace TerminalView component on workspace load; endpoint is `/ws-pty/:runId` where `runId` comes from `POST /api/run`. Frames are raw PTY output (stdin echoes, command output, prompt updates, terminal control sequences) as binary blobs; the client feeds each frame to xterm.js for live rendering. The same tmux session can have multiple simultaneous clients (browser Workspace, `agenthub workspace shell`, other tools), all receiving the same frames live-synced. **The attach URL carries the client's size** (`/ws-pty/:runId?cols=<n>&rows=<n>`, integers in `[2, 1000]`, else 80×24): tmux resizes the window to whichever client attached most recently, so spawning the attach at a default size and correcting it from the first `resize` message a beat later made the pane's program redraw its whole UI at 80 columns — and everything painted at that width stayed in the scrollback, surfacing as torn left-margin fragments the moment the user scrolled back (issue #33). Resize events after that: the client sends a `{"type":"resize","cols","rows"}` text frame and the server applies it as a `TIOCSWINSZ` ioctl down the pane's pty, so window-sensitive commands (e.g. pagers, text editors) adapt to the viewport size. The client reports its size from **xterm's own `onResize`**, not from the container's `ResizeObserver` — cols also move when the webfont finishes loading or the page zooms, neither of which resizes the observed element — and takes the lead whenever the terminal regains focus. **Several browsers on one pane share ONE size** (`server/lib/pty-attach.js`): tmux's `window-size latest` snapped the pane to whoever typed last, so two viewers on screens of different sizes kept resizing it under each other and one saw it cropped. The server names a DRIVER per pane — the first attach, then whichever sends `{"type":"resize","cols","rows","drive":true}` (the client does on focus and on a keystroke, never on a mouse report). Every other attach is a follower: its PTY is held at the driver's size, a follower's own `resize` without `drive` is remembered but not applied, and the server tells it `{"type":"size","cols","rows"}` — the client resizes xterm to that grid and scales it down with CSS to fit, so the browser in use decides the size and the others just shrink. A follower attaches at the driver's size, so joining never resizes the pane. When the driver's socket closes the rest get `{"type":"lead"}` and size themselves again. Driver tracking is per server process: a real terminal (`agenthub workspace shell`) or a second dashboard on the same tmux still follows tmux's own `latest` rule. Keeping the two widths equal is not cosmetic: a tmux pane **wider** than xterm makes every over-long row autowrap its tail onto the next row's left margin, and tmux never repaints a row it believes unchanged — so stray characters stay glued to the left edge of blank lines, visible as soon as a scroll repaints history. A zero size (the console collapses with CSS, leaving the container 0×0) is never reported. The WebSocket connection inherits the same loopback same-origin guard and optional token auth as other `/api/*` routes. The client re-attaches automatically 1.5 s after an unexpected close (server restart, network blip) — tmux keeps the session alive, so the re-attach repaints the pane in full. It stops retrying only after the server's one-shot `{"type":"exit"}` frame, which means the pane process itself ended — the Workspace takes that frame as the signal to restore the run setup form, since there is nothing left to attach to. Without that retry a dropped socket left the pane frozen on its last painted frame: it still looked live, but no keystroke and no mouse report (wheel scroll included) reached tmux again.
+A dedicated binary WebSocket stream (not JSON-framed) for tmux-backed PTY transport. Established by the Workspace TerminalView component on workspace load; endpoint is `/ws-pty/:runId` where `runId` comes from `POST /api/run`. Frames are raw PTY output (stdin echoes, command output, prompt updates, terminal control sequences) as binary blobs; the client feeds each frame to xterm.js for live rendering. The same tmux session can have multiple simultaneous clients (browser Workspace, `agenthub workspace shell`, other tools), all receiving the same frames live-synced. **The attach URL carries the client's size** (`/ws-pty/:runId?cols=<n>&rows=<n>`, integers in `[2, 1000]`, else 80×24): tmux resizes the window to whichever client attached most recently, so spawning the attach at a default size and correcting it from the first `resize` message a beat later made the pane's program redraw its whole UI at 80 columns — and everything painted at that width stayed in the scrollback, surfacing as torn left-margin fragments the moment the user scrolled back (issue #33). Resize events after that: the client sends a `{"type":"resize","cols","rows"}` text frame and the server applies it as a `TIOCSWINSZ` ioctl down the pane's pty, so window-sensitive commands (e.g. pagers, text editors) adapt to the viewport size. The client reports its size from **xterm's own `onResize`**, not from the container's `ResizeObserver` — cols also move when the webfont finishes loading or the page zooms, neither of which resizes the observed element — and takes the lead whenever the terminal regains focus. **Several browsers on one pane share ONE size** (`server/lib/pty-attach.js`): tmux's `window-size latest` snapped the pane to whoever typed last, so two viewers on screens of different sizes kept resizing it under each other and one saw it cropped. The server names a DRIVER per pane — the first attach, then whichever sends `{"type":"resize","cols","rows","drive":true}` (the client does on focus and on a keystroke, never on a mouse report). Every other attach is a follower: its PTY is held at the driver's size, a follower's own `resize` without `drive` is remembered but not applied, and the server tells it `{"type":"size","cols","rows"}` — the client resizes xterm to that grid and scales it down with CSS to fit, so the browser in use decides the size and the others just shrink. A follower attaches at the driver's size, so joining never resizes the pane. When the driver's socket closes the rest get `{"type":"lead"}` and size themselves again. On Windows every attach is also sent `{"type":"wheel"}`: psmux never turns mouse tracking on for its client, so the browser sends the SGR wheel report (`ESC[<64;1;1M` up, `ESC[<65;1;1M` down) itself while xterm reports no tracking — psmux scrolls, or forwards it to a pane app that tracks the mouse (Claude Code fullscreen). Driver tracking is per server process: a real terminal (`agenthub workspace shell`) or a second dashboard on the same tmux still follows tmux's own `latest` rule. Keeping the two widths equal is not cosmetic: a tmux pane **wider** than xterm makes every over-long row autowrap its tail onto the next row's left margin, and tmux never repaints a row it believes unchanged — so stray characters stay glued to the left edge of blank lines, visible as soon as a scroll repaints history. A zero size (the console collapses with CSS, leaving the container 0×0) is never reported. The WebSocket connection inherits the same loopback same-origin guard and optional token auth as other `/api/*` routes. The client re-attaches automatically 1.5 s after an unexpected close (server restart, network blip) — tmux keeps the session alive, so the re-attach repaints the pane in full. It stops retrying only after the server's one-shot `{"type":"exit"}` frame, which means the pane process itself ended — the Workspace takes that frame as the signal to restore the run setup form, since there is nothing left to attach to. Without that retry a dropped socket left the pane frozen on its last painted frame: it still looked live, but no keystroke and no mouse report (wheel scroll included) reached tmux again.
 
 #### cc_config_changed
 

docs/CLI.md

@@ -288,7 +288,7 @@ Because a workspace's services are fully detached, restarting the dashboard (or
 
 | Command | Description |
 | ------- | ----------- |
-| `agenthub doctor` | Diagnosis: API reachability, hook installation status + path, database path/size/row counts, server uptime and Node version, WS connections, whether `tmux` is on **the server's** PATH (asked via `GET /api/run/tmux` — a systemd `--user` service does not read your shell profile), remote-source status |
+| `agenthub doctor` | Diagnosis: API reachability, hook installation status + path, database path/size/row counts, server uptime and Node version, WS connections, whether `tmux` is on **the server's** PATH (asked via `GET /api/run/tmux` — a systemd `--user` service does not read your shell profile) and, when it is older than the platform needs, how to upgrade it, remote-source status |
 | `agenthub info` | The raw `/api/settings/info` JSON (pipe it to `jq`) |
 | `agenthub export [file.json]` | Full JSON data export (sessions, agents, events, tokens, workflows, dashboard runs, alert rules, pricing) — defaults to a dated filename. Re-importable via `agenthub import-data` |
 | `agenthub cleanup --hours N --days M` | Abandon active sessions idle for `N` hours and/or purge completed sessions older than `M` days |

scripts/plugin-doctor.js

@@ -247,15 +247,12 @@ function systemdStatus() {
  * service can still see a different one — `GET /api/run/tmux` is the server's
  * own answer, and `agenthub doctor` reports that.
  *
- * Also WARN below tmux 3.7, the first with pane scrollbars (`tmux.js` turns
+ * Also WARN below the platform's minimum (`tmux.upgradeAdvice`: psmux 3.4.0
- * them on), and when a new binary still talks to an older running server — a
+ * on Windows, tmux 3.7 elsewhere — the same advice the Workspace shows), and
- * server keeps its version until every tmux session has closed. The doctor
+ * when a new binary still talks to an older running server — a server keeps
- * only says so: it never installs or restarts tmux.
+ * its version until every tmux session has closed. The doctor only says so:
+ * it never installs or restarts tmux.
  */
-const hasScrollbars = (version) => {
-  const m = /(\d+)\.(\d+)/.exec(version || "");
-  return !!m && (Number(m[1]) > 3 || (Number(m[1]) === 3 && Number(m[2]) >= 7));
-};
 
 function tmuxStatus() {
   const tmux = require("../server/lib/tmux");
@@ -268,26 +265,18 @@ function tmuxStatus() {
         "Install it: sudo apt install tmux / brew install tmux (Windows: run AgentHub under WSL2)",
     ];
   }
-  if (!hasScrollbars(client)) {
+  const advice = tmux.upgradeAdvice(client);
-    return [
+  if (advice) return ["warn", "tmux", `${client} works, but upgrade it: ${advice}`];
-      "warn",
-      "tmux",
-      `${client} works, but terminal panes get a scrollbar only from tmux 3.7. ` +
-        "Upgrade: brew upgrade tmux (macOS); on Linux, when the distro ships an older one " +
-        "(Ubuntu 24.04 has 3.4), build the release from https://github.com/tmux/tmux/releases " +
-        "(needs libevent-dev libncurses-dev bison: ./configure && make && sudo make install)",
-    ];
-  }
   const server = tmux.serverVersion();
-  if (server && !hasScrollbars(server)) {
+  if (server && tmux.upgradeAdvice(server)) {
     return [
       "warn",
       "tmux",
-      `${client} installed, but the running tmux server is ${server} — panes get their ` +
+      `${client} installed, but the running tmux server is ${server} — it is used ` +
-        "scrollbar once every tmux session has closed (or after a reboot)",
+        "until every tmux session has closed (or after a reboot)",
     ];
   }
-  return ["ok", "tmux", `${client} on PATH — the run console can start sessions, with scrollbars`];
+  return ["ok", "tmux", `${client} on PATH — the run console can start sessions`];
 }
 
 function countLegacyHookEntries() {

scripts/test-server.js

@@ -68,6 +68,23 @@ const env = {
 };
 delete env.TMUX;
 delete env.TMUX_PANE;
+// psmux (the WinGet `tmux` on Windows) ignores TMUX_TMPDIR — and 3.3.x its
+// PSMUX_DATA_DIR too — so every tmux call reached the user's REAL server:
+// quit.test.js's Quit killed every live lane pane, and the kill-server below
+// the rest. Only `-L` isolates there, which no env var can add to each call,
+// so on Windows the suites get no tmux at all; theirs skip (or fail) instead.
+if (process.platform === "win32") {
+  const key = Object.keys(env).find((k) => k.toUpperCase() === "PATH");
+  if (key) {
+    env[key] = env[key]
+      .split(path.delimiter)
+      .filter(
+        (d) => !["tmux.exe", "tmux.cmd", "tmux.bat"].some((f) => fs.existsSync(path.join(d, f)))
+      )
+      .join(path.delimiter);
+  }
+  delete env.PSMUX_SESSION;
+}
 // Git exports these to a hook it runs from a linked worktree (the pre-commit
 // hook runs this suite): inherited, every `git init`/`commit` a test makes in
 // its temp folder went to the REAL repository instead — commits on the

server/__tests__/plugin-doctor-tmux.test.js

@@ -3,9 +3,10 @@
  * an install its browser run console cannot work, because every run the
  * dashboard starts is a tmux session (server/lib/tmux.js). The row must WARN
  * and never FAIL: sessions, analytics, lanes and the CLI all work without the
- * binary, so failing a doctor run over it would cry wolf. A tmux older than 3.7
+ * binary, so failing a doctor run over it would cry wolf. A tmux older than its
- * (no pane scrollbars) also warns, as does a new binary still talking to an
+ * platform asks for (tmux.upgradeAdvice: psmux 3.4.0 on Windows, tmux 3.7
- * older running server. tmux is faked through the module's own exec seam, so
+ * elsewhere) also warns, as does a new binary still talking to an older
+ * running server. tmux is faked through the module's own exec seam, so
  * the test never depends on the host having it.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
@@ -56,18 +57,18 @@ describe("plugin-doctor: tmux row", () => {
     assert.equal(rowWithTmux("next-3.8", "3.8-rc3").level, "ok");
   });
 
-  it("warns, with the upgrade path, when tmux is older than 3.7", () => {
+  it("warns, with this platform's upgrade path, when tmux is older than it asks for", () => {
-    const row = rowWithTmux("3.4", "3.4");
+    // 2.9 is too old everywhere; the advice (minimum, command) is per platform.
+    const row = rowWithTmux("2.9", "2.9");
 
     assert.equal(row.level, "warn");
-    assert.match(row.detail, /3\.7/);
+    assert.ok(row.detail.includes(tmux.upgradeAdvice("2.9")), row.detail);
-    assert.match(row.detail, /brew upgrade tmux/);
   });
 
   it("warns when a new tmux is still talking to an older running server", () => {
-    const row = rowWithTmux("3.7c", "3.4");
+    const row = rowWithTmux("3.7c", "2.9");
 
     assert.equal(row.level, "warn");
-    assert.match(row.detail, /server is 3\.4/);
+    assert.match(row.detail, /server is 2\.9/);
   });
 });

server/__tests__/pty-attach.test.js

@@ -116,7 +116,8 @@ describe("pty-attach", () => {
 
   it("wires PTY data to binary WS frames and WS binary frames to PTY writes", () => {
     const ws = makeFakeWs();
-    ptyAttach.attach(ws, "agenthub-lane-1", { cols: 80, rows: 24 });
+    // Linux: a Windows attach also says `wheel` first (its own test below).
+    ptyAttach.attach(ws, "agenthub-lane-1", { cols: 80, rows: 24, platform: "linux" });
 
     fakePty.__emitter.emit("data", "hello from claude");
     assert.equal(ws.__sent.length, 1);
@@ -269,4 +270,21 @@ describe("attachBinary on Windows", () => {
     }
     tmux.__reset();
   });
+
+  it("tells a Windows attach to send the wheel itself (psmux never tracks the mouse)", () => {
+    for (const [platform, told] of [
+      ["win32", true],
+      ["linux", false],
+    ]) {
+      const ws = makeFakeWs();
+      ptyAttach.attach(ws, "agenthub-lane-1", { cols: 80, rows: 24, platform });
+      const said = ws.__sent.filter((m) => !m.binary).map((m) => JSON.parse(m.data));
+      assert.equal(
+        said.some((m) => m.type === "wheel"),
+        told,
+        platform
+      );
+      ptyAttach.__resetGroups();
+    }
+  });
 });

server/__tests__/run.test.js

@@ -190,6 +190,15 @@ describe("/api/run", () => {
     tmux.__setExecImpl(() => "tmux 3.4");
     const { body } = await fetchJson("/api/run/tmux");
     assert.equal(body.available, true);
+    // The version and this platform's upgrade advice (null when new enough).
+    assert.equal(body.version, "3.4");
+    assert.equal(body.upgrade, tmux.upgradeAdvice("3.4"));
+  });
+
+  it("GET /tmux says to upgrade a version older than the platform asks for", async () => {
+    tmux.__setExecImpl(() => "tmux 2.9");
+    const { body } = await fetchJson("/api/run/tmux");
+    assert.match(body.upgrade, /older than/);
   });
 
   it("GET /cwds still returns suggested directories (unchanged behavior)", async () => {

server/__tests__/tmux.test.js

@@ -326,4 +326,21 @@ describe("tmux wrapper", () => {
     });
     assert.equal(tmux.isTmuxAvailable(), false);
   });
+  it("upgradeAdvice asks each platform for its own minimum, with its own command", () => {
+    // Windows: psmux before 3.4.0 (the WinGet `tmux`).
+    assert.match(
+      tmux.upgradeAdvice("3.3.2", "win32"),
+      /psmux 3\.3\.2 .*3\.4\.0.*winget upgrade marlocarlo\.psmux/
+    );
+    assert.equal(tmux.upgradeAdvice("3.4.0", "win32"), null);
+    assert.equal(tmux.upgradeAdvice("3.10.1", "win32"), null);
+    // macOS / Linux: tmux before 3.7 (pane scrollbars).
+    assert.match(tmux.upgradeAdvice("3.4", "darwin"), /brew upgrade tmux/);
+    assert.match(tmux.upgradeAdvice("3.4", "linux"), /github\.com\/tmux\/tmux\/releases/);
+    assert.equal(tmux.upgradeAdvice("3.7c", "linux"), null);
+    assert.equal(tmux.upgradeAdvice("next-3.8", "darwin"), null);
+    // Nothing to compare: no advice rather than a wrong one.
+    assert.equal(tmux.upgradeAdvice(null, "linux"), null);
+    assert.equal(tmux.upgradeAdvice("3.3.2", "freebsd"), null);
+  });
 });

server/lib/pty-attach.js

@@ -136,6 +136,11 @@ function attach(ws, runId, { cols, rows, platform = process.platform }) {
   group.viewers.add(me);
   if (lead) tell(me, { type: "size", cols: lead.cols, rows: lead.rows });
   else group.driver = me;
+  // psmux never turns mouse tracking on for its client (not even for a pane
+  // app that asked), so xterm.js would never report the wheel and the pane
+  // could not scroll. psmux does act on a wheel report it receives: the
+  // browser sends one itself (TerminalView).
+  if (platform === "win32") tell(me, { type: "wheel" });
 
   // Backpressure: a slow viewer (a remote browser on a thin link) must not
   // queue a chatty pane's output in this process without bound. Past 1 MB

server/lib/tmux.js

@@ -695,6 +695,40 @@ function clientVersion() {
   }
 }
 
+// The oldest tmux AgentHub asks for, and how each platform upgrades it.
+// Windows' is psmux: before 3.4.0 a dashboard terminal stalled until a
+// refresh, and fixes for frame push, writes and synchronized output landed in
+// 3.3.6–3.4.0. Elsewhere 3.7, the first with pane scrollbars (enableMouse).
+const UPGRADES = {
+  win32: {
+    min: [3, 4, 0],
+    name: "psmux",
+    how: "close every AgentHub terminal pane, then run: winget upgrade marlocarlo.psmux",
+  },
+  darwin: { min: [3, 7, 0], name: "tmux", how: "brew upgrade tmux" },
+  linux: {
+    min: [3, 7, 0],
+    name: "tmux",
+    how:
+      "distros ship older ones (Ubuntu 24.04 has 3.4), so build the release from " +
+      "https://github.com/tmux/tmux/releases (needs libevent-dev libncurses-dev bison: " +
+      "./configure && make && sudo make install)",
+  },
+};
+
+/** What to tell the user when `version` is older than their platform asks
+ *  for; null when it is new enough or cannot be compared. Advice only —
+ *  AgentHub never installs or restarts tmux. */
+function upgradeAdvice(version = clientVersion(), platform = process.platform) {
+  const want = UPGRADES[platform];
+  const m = /(\d+)\.(\d+)(?:\.(\d+))?/.exec(version || "");
+  if (!want || !m) return null;
+  const have = [m[1], m[2], m[3] || 0].map(Number);
+  const i = have.findIndex((n, k) => n !== want.min[k]);
+  if (i === -1 || have[i] > want.min[i]) return null;
+  return `${want.name} ${version} is older than ${want.min.join(".")} — ${want.how}`;
+}
+
 /** The RUNNING server's version, null when none runs. A server started before
  *  an upgrade keeps its old version until every tmux session has closed. */
 function serverVersion() {
@@ -725,6 +759,7 @@ module.exports = {
   isTmuxAvailable,
   clientVersion,
   serverVersion,
+  upgradeAdvice,
   serverPid,
   memberAttach,
   __setExecImpl,

server/routes/run.js

@@ -423,7 +423,14 @@ router.get("/binary", (req, res) => {
 });
 
 router.get("/tmux", (_req, res) => {
-  res.json({ available: tmux.isTmuxAvailable() });
+  // `upgrade`: this platform's advice when the binary is older than AgentHub
+  // asks for (tmux.upgradeAdvice), else null. The Workspace shows it.
+  const version = tmux.clientVersion();
+  res.json({
+    available: version !== null,
+    version,
+    upgrade: version ? tmux.upgradeAdvice(version) : null,
+  });
 });
 
 router.post("/", (req, res) => {