fix: v2.5.7 — panes work on psmux, the Windows tmux

psmux (the WinGet `tmux` on Windows) has no `=name` exact-match targets: it
answered "no server running on session '=agenthub-lane-1'" for a live pane,
so every Windows start reported "the session's command exited as soon as it
started" while the session ran on, and the browser could not attach.

- server/lib/tmux.js: `session`/`pane` targets probe the first live session
  once — `=name` failing where the bare name answers means bare names from
  then on; real tmux keeps `=name` / `=name:` (it matches by prefix otherwise)
- pty-attach.js and cc-update-all-helper.js use the same targets

server/__tests__/tmux.test.js

@@ -51,6 +51,36 @@ describe("tmux wrapper", () => {
     assert.deepEqual(calls[0], ["new-session", "-d", "-s", "agenthub-lane-1", "-c", "C:\\repo"]);
   });
 
+  it("names sessions bare on psmux, which has no `=name` targets, and keeps `=` on tmux", () => {
+    // psmux (the WinGet `tmux` on Windows) answers "no server running on
+    // session '=agenthub-lane-1'" for a session that is alive, so every
+    // `=` target read a live pane as gone.
+    const fake = (supportsExact) => {
+      const calls = [];
+      tmux.__setExecImpl(
+        (args) => {
+          calls.push(args);
+          if (args[0] === "list-sessions") return "agenthub-lane-1\n";
+          const t = args[args.indexOf("-t") + 1];
+          if (t && t.startsWith("=") && !supportsExact) throw new Error("no server running");
+          return "";
+        },
+        { exact: null }
+      );
+      return calls;
+    };
+
+    let calls = fake(false);
+    assert.equal(tmux.hasSession("agenthub-lane-1"), true);
+    tmux.enableMouse("agenthub-lane-1");
+    assert.ok(calls.some((c) => c[0] === "set-option" && c[2] === "agenthub-lane-1"));
+    assert.ok(!calls.some((c) => c[0] === "set-option" && c[2].startsWith("=")));
+
+    calls = fake(true);
+    tmux.enableMouse("agenthub-lane-1");
+    assert.ok(calls.some((c) => c[0] === "set-option" && c[2] === "=agenthub-lane-1:"));
+  });
+
   it("newSession builds the correct argv", () => {
     const calls = [];
     tmux.__setExecImpl((args) => {