monotonic-pi-extensions/limit-turns.ts

import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";

// ============================================================================
// Configuration
// ============================================================================

const DEFAULT_MAX_TURNS = 25;

function getMaxTurns(): number {
  const env = process.env.PI_MAX_TURNS;
  if (!env) return DEFAULT_MAX_TURNS;
  const parsed = parseInt(env, 10);
  return Number.isFinite(parsed) && parsed > 0 ? parsed : DEFAULT_MAX_TURNS;
}

// ============================================================================
// Pure detection logic (testable)
// ============================================================================

export function checkTurnLimit(
  turnIndex: number,
  maxTurns: number,
): { exceeded: boolean; turnIndex: number; maxTurns: number } {
  return {
    exceeded: turnIndex > maxTurns,
    turnIndex,
    maxTurns,
  };
}

// ============================================================================
// Extension handler
// ============================================================================

export default function (pi: ExtensionAPI) {
  let turnCount = 0;
  const maxTurns = getMaxTurns();

  pi.on("agent_start", async (_event, ctx) => {
    // Reset counter for each new user prompt
    turnCount = 0;
  });

  pi.on("turn_start", async (event, ctx) => {
    turnCount++;

    const { exceeded } = checkTurnLimit(event.turnIndex, maxTurns);
    if (exceeded && ctx.hasUI) {
      ctx.ui.notify(
        `Turn limit exceeded: ${maxTurns} turns reached. Agent aborted.`,
        "error",
      );
      ctx.abort();
    }
  });
}