app/tui/fullscreen.ts

 // Puts the terminal into its alternate screen buffer for the life of

 // the process, the way a real full-screen app (less, vim, Textual's own

 // apps) does -- so the TUI occupies a stable viewport instead of

 // printing into (and growing) the shell's normal scrollback. Restores

 // the original screen on any exit path so the shell is left clean.

 //

 // Also enables mouse reporting (click + wheel, SGR encoding) so the

 // scroll wheel can drive the same scroll actions as the arrow keys (see

 // useMouseWheel.ts) -- the one real tradeoff this introduces is that a

 // plain click-drag no longer starts the terminal's own text selection,

 // since button presses now go to the app instead. Hold Option (macOS)

 // or Shift (most other terminals) while clicking/dragging to force the

 // terminal to select text natively anyway -- a standard convention, not

 // a workaround specific to this app.

 let active = false;

 // Separate from `active` because enterFullscreen can now be called more

 // than once per process (AssistApp's ctrl+t shell toggle leaves and

 // re-enters it) -- the exit/SIGINT/SIGTERM handlers only need

 // registering the first time, not once per re-entry, or they'd pile up

 // across however many times someone hops in and out of a shell.

 let listenersAttached = false;

 export function enterFullscreen(): void {

  if (active) return;

  active = true;

  process.stdout.write("\x1B[?1049h"); // switch to alternate screen buffer

  process.stdout.write("\x1B[2J\x1B[H"); // clear it, cursor to home

  process.stdout.write("\x1B[?25l"); // hide cursor

  process.stdout.write("\x1B[?1000h"); // enable mouse reporting (click + wheel)

  process.stdout.write("\x1B[?1006h"); // SGR extended mouse encoding

  if (listenersAttached) return;

  listenersAttached = true;

  const restore = () => exitFullscreen();

  process.on("exit", restore);

  process.on("SIGINT", () => {

  restore();

  process.exit(0);

  });

  process.on("SIGTERM", () => {

  restore();

  process.exit(0);

  });

 }

 export function exitFullscreen(): void {

  if (!active) return;

  active = false;

  process.stdout.write("\x1B[?1006l");

  process.stdout.write("\x1B[?1000l");

  process.stdout.write("\x1B[?25h"); // show cursor

  process.stdout.write("\x1B[?1049l"); // restore the normal screen buffer

 }