GCC Build Failure: A Debugging Mystery Caused by sbuild Refactoring

Official Debian GCC builds started failing mysteriously after an sbuild refactoring. A team embarked on a six-stage investigation, ultimately uncovering a conflict between the new sbuild init system and a D language unit test. The test accidentally terminated its own process group, halting the build. The root cause was the use of -2 as a special PID value in the D language unit test, leading to SIGTERM signals being sent to the wrong process group. Switching back to the old init system or modifying the test code resolved the issue.