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/lib/pty-attach.js

@@ -12,6 +12,8 @@
  * the driver's size and told so (`{type:"size", cols, rows}`) so its xterm
  * renders the same grid, scaled to fit, instead of each browser resizing tmux
  * under the others. A driver that leaves sends `{type:"lead"}` to the rest.
+ * A keystroke that follows a mouse report first takes the pane out of tmux's
+ * copy-mode (the wheel's scrollback), so typing never lands in it.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -73,7 +75,16 @@ function attachBinary(platform = process.platform) {
 // the paste in that issue's measurements.
 const PASTE_HOLD_MS = 700;
 
-// runId -> { driver, viewers: Set<{ ws, pty, cols, rows }> }
+// Input that is not typing: a mouse report (SGR `ESC[<b;x;yM`, X10 `ESC[M` +
+// three bytes) or a focus in/out. A wheel report is what puts a pane into
+// tmux's copy-mode, where every typed key is taken as a scrollback command —
+// the pane looked frozen. So once a mouse report has passed, the next real
+// keystroke first leaves copy-mode (`tmux.leaveCopyMode`), then is written.
+const NOT_TYPING_RE = /\x1b\[<\d+;\d+;\d+[Mm]|\x1b\[M[\s\S]{3}|\x1b\[[IO]/g;
+
+// runId -> { driver, viewers: Set<{ ws, pty, cols, rows }>, scrolled }
+// (`scrolled`: a mouse report reached the pane since the last keystroke — per
+// pane, since one browser may scroll and another type)
 const groups = new Map();
 
 const tell = (v, msg) => {
@@ -211,6 +222,16 @@ function attach(ws, runId, { cols, rows, platform = process.platform }) {
       /* the attach exited while its input was held — nothing to write to */
     }
   };
+  // Keystrokes after a scroll leave copy-mode first; see NOT_TYPING_RE.
+  function input(text) {
+    if (text.replace(NOT_TYPING_RE, "") === "") {
+      if (text.includes("\x1b[M") || text.includes("\x1b[<")) group.scrolled = true;
+    } else if (group.scrolled) {
+      group.scrolled = false;
+      tmux.leaveCopyMode(runId);
+    }
+    write(text);
+  }
   function write(text) {
     if (me.exited) return; // the attach is gone: nothing reads this pipe
     const wait = holdUntil - Date.now();
@@ -248,7 +269,7 @@ function attach(ws, runId, { cols, rows, platform = process.platform }) {
     const binary = typeof isBinary === "boolean" ? isBinary : !!(isBinary && isBinary.binary);
     const text = data.toString("utf8");
     if (binary) {
-      write(text);
+      input(text);
       return;
     }
     // The browser's WebSocket API sends a JS string as a text frame, and
@@ -262,7 +283,7 @@ function attach(ws, runId, { cols, rows, platform = process.platform }) {
       try {
         msg = JSON.parse(text);
       } catch {
-        write(text);
+        input(text);
         return;
       }
       if (msg && msg.type === "resize" && Number.isFinite(msg.cols) && Number.isFinite(msg.rows)) {
@@ -274,7 +295,7 @@ function attach(ws, runId, { cols, rows, platform = process.platform }) {
         return;
       }
     }
-    write(text);
+    input(text);
   });
 
   ws.on("close", () => {