fix(tmux): scrolling a pane no longer freezes typing

The wheel puts a pane into tmux's copy-mode, which took every typed key as
a scrollback command and painted a yellow [0/0] box in the corner. In
AgentHub's own panes (every other session on the server keeps tmux's
defaults, restored verbatim):

- the copy-mode position box is off (copy-mode-position-format "");
- the first keystroke after a mouse report leaves copy-mode
  (`copy-mode -q`, pty-attach) before it is written, once per scroll;
- copy-mode keys that open a tmux prompt (g, :, /, f, digits…) leave
  copy-mode and reach the program;
- the wheel scrolls 10 lines a notch instead of 5, and the first notch
  already scrolls instead of only entering copy-mode.

server/__tests__/tmux.test.js

@@ -183,9 +183,18 @@ describe("tmux wrapper", () => {
     calls = fake(true);
     tmux.enableMouse("agenthub-lane-1");
     assert.ok(calls.some((c) => c[0] === "set-option" && c[2] === "=agenthub-lane-1:"));
-    // tmux chains the four options into two spawns; psmux above got four.
+    // tmux chains the four options into two spawns, plus the copy-mode
+    // position box (a newer tmux only) in its own; psmux above got five.
     const sets = calls.filter((c) => c[0] === "set-option");
-    assert.equal(sets.length, 2);
+    assert.equal(sets.length, 3);
+    assert.deepEqual(sets[2], [
+      "set-option",
+      "-w",
+      "-t",
+      "=agenthub-lane-1:",
+      "copy-mode-position-format",
+      "",
+    ]);
     assert.deepEqual(sets[0], [
       "set-option",
       "-t",
@@ -235,7 +244,39 @@ describe("tmux wrapper", () => {
       ...["set-option", "-t", "=agenthub-lane-1:", "pane-scrollbars-style"],
       "fg=brightwhite,bg=black,width=1,pad=0",
     ]);
-    assert.equal(calls.length, 3);
+    // No yellow `[0/0]` box in the corner while the wheel's copy-mode is on.
+    assert.deepEqual(calls[3], [
+      ...["set-option", "-w", "-t", "=agenthub-lane-1:", "copy-mode-position-format", ""],
+    ]);
+    // Copy-mode keys that open a prompt ("(goto line)"…) leave copy-mode and
+    // reach the program in OUR sessions only; others keep tmux's default.
+    assert.deepEqual(calls[4].slice(0, 9), [
+      ...["bind-key", "-T", "copy-mode", "g", "if-shell", "-F"],
+      "#{m:agenthub-lane-*,#{session_name}}",
+      "send-keys -X cancel ; send-keys -l -- 'g'",
+      'command-prompt -P -p "(goto line)" { send-keys -X goto-line -- "%%" }',
+    ]);
+    assert.ok(calls[4].includes(":"), "vi's `:` goto-line is re-bound too");
+    // The wheel scrolls 10 lines a notch in OUR panes, 5 (tmux's) elsewhere.
+    assert.deepEqual(calls[5].slice(0, 9), [
+      ...["bind-key", "-T", "root", "WheelUpPane", "if-shell", "-F"],
+      "#{||:#{alternate_on},#{pane_in_mode},#{mouse_any_flag}}",
+      "send-keys -M",
+      'if-shell -F "#{m:agenthub-lane-*,#{session_name}}" { copy-mode -e ; send-keys -X -N 10 scroll-up } { copy-mode -e }',
+    ]);
+    assert.ok(calls[5].includes("select-pane ; send-keys -X -N 10 scroll-down"));
+    assert.ok(calls[5].includes("select-pane ; send-keys -X -N 5 scroll-down"));
+    assert.equal(calls.length, 6);
+  });
+
+  it("newSession still succeeds when tmux refuses the copy-mode bindings", () => {
+    tmux.__setExecImpl((args) => {
+      if (args[0] === "bind-key") throw new Error("unknown flag -F");
+      return "";
+    });
+    assert.doesNotThrow(() =>
+      tmux.newSession({ name: "agenthub-lane-1", cwd: "/tmp/repo", argv: ["claude"] })
+    );
   });
 
   it("newSession still succeeds on a tmux older than 3.7 (no pane-scrollbars)", () => {