v4 crashes with `node --watch` on Node.js v26

[Vunovati]

v4 crashes with Error: this should not happen: undefined under node --watch on Node.js v26

thread-stream@4.0.0 / pino@10.3.1 / Node.js v26.1.0

With --watch enabled, any 2-target transport setup crashes immediately on startup:

node:events:487
      throw er; // Unhandled 'error' event
      ^

Error: this should not happen: undefined
    at Worker.onWorkerMessage (thread-stream/index.js:190:23)
    at Worker.emit (node:events:509:20)
    at MessagePort.<anonymous> (node:internal/worker:358:14)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:843:20)
    at MessagePort.<anonymous> (node:internal/per_context/messageport:23:28)
Emitted 'error' event on ThreadStream instance at:
    at Immediate.<anonymous> (thread-stream/index.js:371:12)

Node.js v26.1.0
Failed running 'index.js'. Waiting for file changes before restarting...

Two targets are required to hit this — pino only spawns a ThreadStream worker when targets.length >= 2.

Minimal repro:

const pino = require('pino')

const logger = pino({
  transport: {
    targets: [
      {
        target: 'pino-opentelemetry-transport',
        options: { resourceAttributes: { 'service.name': 'repro' } },
        level: 'info',
      },
      {
        target: 'pino/file',
        options: { destination: 1 },
        level: 'info',
      },
    ],
  },
})

logger.info('hello world')
setTimeout(() => {}, 60000)

node --watch index.js  # crashes (Node.js v26)

Full repro repo

with Docker: https://github.com/Vunovati/repro-pino-otel

Node.js	--watch	result
v24	yes	✅ works
v26	no	✅ works
v26	yes	❌ crashes

Node.js v26 is not yet in the pino CI matrix — flagging this as a heads-up ahead of that.

Possible cause

Node.js v26 landed nodejs/node#62368 ("watch: track worker entry files in watch mode"), which sends messages through the worker's parentPort without a code field.

I believe this breaks thread-stream's onWorkerMessage where it finds msg.code === undefined index.js#L190.