JIT bug: composer install sometimes hangs

Description

composer install sometimes hangs when JIT is on and set to tracing. I created a reproducing repo that shows the problem: https://github.com/ondrejmirtes/composer-hang-repro

Disclaimer: Claude Code helped me create the reproducer. The repo contains two Dockerfiles (with JIT on/off) that shows the difference in behaviour and loop.sh script that runs composer install over and over and shows that it hangs in about 3 % of performed runs.

There are some details in the README but consider them with a grain of salt.

To reproduce the problem in the cloned link repository:

# Build both images (PHP 8.5.6 + Composer 2.9.5)
docker build -t composer-jit-hang  -f Dockerfile.jit  .
docker build -t composer-jit-nojit -f Dockerfile.nojit .

# 1) See the hang with opcache.jit=tracing.
#    loop.sh bootstraps vendor/ on first run (one ~30 s install to bring in
#    Symfony Flex, which has to be loaded as a plugin for the JIT bug to
#    fire), then runs `composer install --dry-run` 200 times. Expect a
#    handful of those runs to be killed at the 15 s deadline — last
#    measurement: 19 hangs in 500 runs.
docker run --rm \
  -v "$PWD":/work \
  composer-jit-hang bash /loop.sh 200

# 2) Same project, same Composer, same PHP, JIT off — zero hangs.
docker run --rm \
  -v "$PWD":/work \
  composer-jit-nojit bash /loop.sh 200

PHP Version

PHP 8.5.6 (cli) (built: May  8 2026 19:23:57) (NTS)
     Copyright (c) The PHP Group
     Built by https://github.com/docker-library/php

Operating System

Debian 13.4

Clone repository composer-hang-repro được liên kết và bắt đầu bằng cách build Dockerfile.jit và Dockerfile.nojit, sau đó chạy loop.sh để so sánh các lần cài đặt Composer lặp lại. Đọc README và kiểm tra hành vi PHP JIT/OPcache liên quan trong cấu hình tracing. Hoàn tất có nghĩa là các hiện tượng treo được minh họa đã được hiểu rõ và không còn xảy ra trong reproducer khi tracing được bật.