Copilot CLI + RTK, put at ~/.copilot/extensions/rtk-rewrite/extension.mjs

extension.mjs

import { spawn } from "node:child_process";
import { approveAll } from "@github/copilot-sdk";
import { joinSession } from "@github/copilot-sdk/extension";

// Pipes bash onPreToolUse events through rtk hook copilot, which rewrites
// commands to their rtk-equivalent for token savings (e.g. git status → rtk git status).
// Safe no-op if rtk is not installed or returns no rewrite.
//
// Input shape: app.js calls extensions via FCs() which produces { toolName, toolArgs }
// per individual tool call. toolArgs may be a JSON string (OpenAI wire format) or
// already-parsed object depending on CLI version — handle both defensively.
function runRtk(input) {
  let toolInput;

  if (input.toolName) {
    if (input.toolName !== "bash") return Promise.resolve({});
    toolInput = typeof input.toolArgs === "string"
      ? JSON.parse(input.toolArgs)
      : input.toolArgs;
  } else if (input.toolCalls) {
    const call = input.toolCalls.find(c => c.name === "bash");
    if (!call) return Promise.resolve({});
    try { toolInput = JSON.parse(call.args); } catch { return Promise.resolve({}); }
  } else {
    return Promise.resolve({});
  }

  return new Promise((resolve) => {
    const proc = spawn("rtk", ["hook", "copilot"], { timeout: 5000 });
    let stdout = "";
    proc.stdout.on("data", (d) => (stdout += d));
    proc.on("close", () => {
      try {
        const hook = JSON.parse(stdout)?.hookSpecificOutput;
        if (hook?.updatedInput) {
          // Merge back fields rtk drops (e.g. description) — CLI validates all required fields
          resolve({ permissionDecision: "allow", modifiedArgs: { ...toolInput, ...hook.updatedInput } });
        } else {
          resolve({});
        }
      } catch { resolve({}); }
    });
    proc.on("error", () => resolve({}));
    proc.stdin.write(JSON.stringify({ tool_name: "bash", tool_input: toolInput }));
    proc.stdin.end();
  });
}

await joinSession({
  onPermissionRequest: approveAll,
  hooks: {
    onPreToolUse: async (input) => runRtk(input),
  },
});