pi extension: hide the prompt cursor when the terminal pane loses focus (tmux focus-events), so it's obvious which split pi you're typing into

cursor-focus.ts

// Replace pi's fake reverse-video prompt cursor with the terminal's native
// hardware cursor.
//
// pi already emits CURSOR_MARKER at the correct editor position. Enabling the
// hardware cursor makes pi-tui position the terminal cursor at that marker;
// removing the fake reverse-video block prevents two cursors from overlapping.
// tmux and the terminal then provide their native focus behavior:
//
// - active tmux pane, focused terminal: normal hardware cursor
// - active tmux pane, unfocused terminal: terminal's inactive cursor style
// - inactive tmux pane: no cursor

import { CustomEditor, type ExtensionAPI } from "@earendil-works/pi-coding-agent";
import type { KeybindingsManager } from "@earendil-works/pi-coding-agent";
import type { EditorTheme, TUI } from "@earendil-works/pi-tui";

// pi's fake cursor is reverse video around the grapheme under the cursor (or a
// space at end of input). CURSOR_MARKER precedes this sequence and is preserved.
const FAKE_CURSOR = /\x1b\[7m([\s\S]*?)\x1b\[0m/g;

class NativeCursorEditor extends CustomEditor {
  private readonly hardwareCursorTui: TUI;

  constructor(tui: TUI, theme: EditorTheme, keybindings: KeybindingsManager) {
    super(tui, theme, keybindings);
    this.hardwareCursorTui = tui;
    tui.setShowHardwareCursor(true);
  }

  render(width: number): string[] {
    // On /reload pi fires session_start (which reinstalls this editor and turns
    // the hardware cursor on) and only afterwards runs applyRuntimeSettings(),
    // which resets the hardware cursor to the settings default. That would leave
    // no cursor at all: the fake reverse-video cursor is stripped below while the
    // hardware cursor is off. Re-assert it every render so the native cursor
    // survives a reload. setShowHardwareCursor early-returns when unchanged, so
    // this is idempotent and only triggers a render on the frame it flips back on.
    this.hardwareCursorTui.setShowHardwareCursor(true);
    return super.render(width).map((line) => line.replace(FAKE_CURSOR, "$1"));
  }
}

export default function (pi: ExtensionAPI) {
  pi.on("session_start", (_event, ctx) => {
    if (ctx.mode !== "tui") return;
    ctx.ui.setEditorComponent(
      (tui, theme, keybindings) => new NativeCursorEditor(tui, theme, keybindings),
    );
  });
}

Correction: the extension is still needed for tmux pane focus

Pi's built-in showHardwareCursor setting only makes the terminal cursor visible for IME positioning. By design, Pi continues rendering its fake reverse-video cursor as well.

That means an inactive tmux pane hides the hardware cursor, but the painted fake cursor remains visible. This extension is still required to strip the fake cursor and get native tmux/terminal focus behavior.