reparser:reparse breaks quietly

We're upgrading from an earlier version of phpBB and trying to integrate the reparser:reparse step into the automated conversion-process. Invoked as

php bin/phpbbcli.php reparser:reparse --ansi

the program runs for a while, but exits abruptly 54% through pm_text. The exit code is 255, but there are no error-messages displayed – despite the prior output being otherwise verbose and colorful.

The error_log in the phpBB directory contains:

[12-Jun-2021 23:27:35 America/New_York] PHP Fatal error:  SQL ERROR [ mysqli ]<br /><br />MySQL server has gone away [2006]<br /><br />An SQL error occurred while fetching this page. Please contact the <a href="mailto:x@x">Board Administrator</a> if this problem persists. in /home/.../phpbb/db/driver/driver.php on line 1023

Note, this is not a "support request", I'm reporting the following bugs with the tool:

1. The error is not output to the stderr – one has to look for it in the log.
2. The error is in (some semblance of) HTML format – perhaps, rendered nicely by browsers, but difficult to read by command-line users.
3. Subsequent attempts to invoke reparser fail due to "REPARSE_LOCK_ERROR" – this one is displayed on a loud red background, no problem. But:
   • No advice is provided on how to clear the lock
   • The code needs a way to check its lock for being stale – perhaps, by recording the hostname/PID in the DB, instead of simply 1.
4. Finally, having the MySQL server "go away" on the same post is, probably, an indication of an actual bug. And, even if a post cannot be converted automatically for whatever reason, the tool ought to:
   • identify the item (table and ID) for manual fixing
   • keep going!