PHP8.1 tests failing because blackfire doesn't work on PHP 8.1

[rfay]

Preliminary checklist

• I am using the latest stable version of DDEV
• I am using the latest stable version of this add-on

Expected Behavior

See https://github.com/ddev/ddev-platformsh/actions/runs/18980071572/job/54212340665

DDEV HEAD tests are failing on drupal9 and wordpress-composer. Both of those templates use PHP8.1, and current blackfire seems to be broken on them.

Actual Behavior

It seems that blackfire just stopped working with Debian Bookworm on PHP 8.1. This showed up on DDEV's tests of ddev-platformsh, which has a drupal9 test using the old platformsh template, which uses PHP 8.1

rfay@x-web:/var/www/html$ php --version
PHP 8.1.33 (cli) (built: Jul  3 2025 16:25:40) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.33, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.33, Copyright (c), by Zend Technologies
rfay@x-web:/var/www/html$ phpenmod blackfire
rfay@x-web:/var/www/html$ php --version
PHP Warning:  PHP Startup: Unable to load dynamic library 'blackfire.so' (tried: /usr/lib/php/20210902/blackfire.so (/usr/lib/php/20210902/blackfire.so: cannot open shared object file: No such file or directory), /usr/lib/php/20210902/blackfire.so.so (/usr/lib/php/20210902/blackfire.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0

Warning: PHP Startup: Unable to load dynamic library 'blackfire.so' (tried: /usr/lib/php/20210902/blackfire.so (/usr/lib/php/20210902/blackfire.so: cannot open shared object file: No such file or directory), /usr/lib/php/20210902/blackfire.so.so (/usr/lib/php/20210902/blackfire.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
PHP 8.1.33 (cli) (built: Jul  3 2025 16:25:40) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.33, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.33, Copyright (c), by Zend Technologies
rfay@x-web:/var/www/html$ dpkg -l blackfire
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-===================================================================
ii  blackfire      2:2.29.2     arm64        Blackfire agent and tools. It replaces the blackfire-agent package.

It worked fine with blackfire v1.92.42 and PHP8.1 (in DDEV v1.24.8)

It no longer works with DDEV HEAD which gets blackfire 2.29.2

I don't see anything about dropping PHP 8.1 support in any of the places, but maybe I don't know where to look.

Posted this in Blackfire Discord, https://discord.com/channels/1121795479785721957/1433898308753031260

Steps To Reproduce

ddev config --php-version=8.1
ddev php --version
ddev blackfire on
ddev php --version

Anything else?

No response