Uncatchable exception on idle in transcation timeout

Hello!

If you trigger a connection termination due to idle in transaction timeout postgres throws an error that is not catchable from the callsite.

Minimal repro:

const postgres = require("postgres");

const sql = postgres({
  host: process.env.PGHOST || "localhost",
  port: process.env.PGPORT ? Number(process.env.PGPORT) : 5432,
  database: process.env.PGDATABASE || "postgres_connection_issue",
  user: process.env.PGUSER,
});

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

async function main() {
  console.log("\n--- minimal idle timeout repro ---");
  try {
    await sql.begin(async (tx) => {
      await tx`SET idle_in_transaction_session_timeout = 50`;
      await sleep(200);
    });
  } catch (err) {
    // The driver throws a normal connection-closed error after the server kills
    // the backend for idling in a transaction. We log that and keep going.
    console.error("caught error:", err?.message || err);
  }
}

process.on("uncaughtException", (err) => {
  console.error("uncaught exception:", err);
});

main();

The stack trace is

    at Immediate.nextWrite ([..]/node_modules/postgres/cjs/src/connection.js:250:22)
    at process.processImmediate (node:internal/timers:483:21)

This seems to be a race condition between nextWrite and the socket being closed.

This becomes a problem because the exception cannot be caught without using process.on, ideally this exception would not be raised.

Start with the minimal reproduction in the issue and inspect connection.js around nextWrite at line 250, focusing on the interaction with the socket closing after the idle-in-transaction timeout. Confirm the uncaught exception and verify that the same scenario completes with the connection-closed error handled at the callsite rather than reaching process.on("uncaughtException").