fix: v2.5.8 — the browser terminal attaches on Windows

node-pty on Windows looks the file it starts up on PATH exactly as given and
never adds `.exe`, so `tmux attach-session` started as a bare `tmux` failed
with "File not found" on every attach: the browser's terminal socket opened,
closed, and reconnected every 1.5 s.

- pty-attach.js: attachBinary names tmux by its full file name on Windows
  (ai-tools.which("tmux"), else tmux.exe)
- websocket.js: an attach that throws is logged as `[WS] attach <run> failed`,
  the one place that says why the terminal keeps reconnecting

server/__tests__/pty-attach.test.js

@@ -169,3 +169,17 @@ describe("pty-attach", () => {
     assert.equal(killed, true);
   });
 });
+
+describe("attachBinary on Windows", () => {
+  it("names tmux with its extension — node-pty there never adds `.exe`", () => {
+    // A bare `tmux` made node-pty answer "File not found" on every attach, so
+    // the browser's terminal opened, closed and reconnected every 1.5 s.
+    const saved = process.env.PATH;
+    process.env.PATH = "";
+    try {
+      assert.equal(ptyAttach.attachBinary("win32"), "tmux.exe");
+    } finally {
+      process.env.PATH = saved;
+    }
+  });
+});