Retry middleware skipped and message sent directly to PoisonQueue when using AddHandler

[s4ndeep4]

Steps to reproduce

docker-compose.yml

version: "3.8"

services:
  nats:
    image: nats:2.10
    ports:
      - "4222:4222"

go

package main

import (
	"errors"
	"time"

	"github.com/ThreeDotsLabs/watermill"
	"github.com/ThreeDotsLabs/watermill/message"
	"github.com/ThreeDotsLabs/watermill/message/router"
	"github.com/ThreeDotsLabs/watermill/message/router/middleware"
	wmnats "github.com/ThreeDotsLabs/watermill-nats/v2/pkg/nats"
)

func main() {
	logger := watermill.NewStdLogger(false, false)

	sub, _ := wmnats.NewSubscriber(
		wmnats.SubscriberConfig{URL: "nats://localhost:4222"},
		logger,
	)

	pub, _ := wmnats.NewPublisher(
		wmnats.PublisherConfig{URL: "nats://localhost:4222"},
		logger,
	)

	r, _ := router.NewRouter(router.Config{}, logger)

	r.AddMiddleware(middleware.Retry{
		MaxRetries:      3,
		InitialInterval: time.Second,
	}.Middleware)

	r.AddMiddleware(middleware.PoisonQueue(pub, "poison.topic"))

	r.AddHandler(
		"test-handler",
		"input.topic",
		sub,
		"output.topic",
		pub,
		func(msg *message.Message) ([]*message.Message, error) {
			return nil, errors.New("simulated error")
		},
	)

	go r.Run(nil)

	_ = pub.Publish("input.topic",
		message.NewMessage(watermill.NewUUID(), []byte("test")),
	)

	select {}
}

Expected behavior

When the handler returns an error and Retry middleware is configured, the handler should be retried according to MaxRetries, and the message should be sent to the poison queue only after retries are exhausted.

Actual behavior

The handler is executed only once and the message is sent directly to the poison queue without retrying.

Possible solution

Clarify in documentation how Retry and PoisonQueue behave when used with AddHandler, or document that AddHandler is intended only for handlers that always publish output messages.