Error handlers that take args: Args crash with a missing 'next' argument #1598

Reproducible in:

The slack_bolt version

slack_bolt==1.30.0
slack_sdk==3.45.0

Python runtime version

Python 3.12.5

OS info

macOS 27.0

Steps to reproduce:

Register a global error handler that takes args: Args.

from slack_bolt import App, Args

app = App(token="xoxb-...", signing_secret="secret")

@app.error
def on_error(error, args: Args):
    args.logger.error(error)

@app.event("app_mention")
def boom(say):
    raise RuntimeError("original error")

1. Trigger the app_mention event.

Expected result:

on_error runs and logs original error.

Actual result:

The error handler itself crashes before it runs:

TypeError: Args.__init__() missing 1 required positional argument: 'next'

The original RuntimeError is lost. In slack_bolt/kwargs_injection/utils.py (build_required_kwargs) and async_utils.py, next is removed from the available arguments for error handlers, but Args(**all_available_args) is then built from that reduced dict, and Args requires next. The same code also uses arg_names.pop() on the listener's own list, so the list shrinks on every call.

I have a fix with sync and async tests in #1592. It also adds an error field to Args so error handlers can read the exception through args.

Requirements

I have read the Contributing guidelines and Code of Conduct.