New Half-Life 2 development lore drop!
It’s a wild ride to read. It’s about a very niche bug that softlocks the game but somehow the bug can travel back in time and even affect the original retail version of Half-Life 2.
TLDR: the bug
The softlock happens because an NPC is standing in the way of a door. This didn’t happen in the original because it was compiled using the old-school Intel x87 floating point handling and not the (relatively) more modern SSE behaviour, which does cause the softlock. The bug managed to time travel to the retail build because modern compilers use SSE instead of x87.
This is actually an incredible coincidence; I love reading these stories but it’s usually in the context of a speedrunner exploiting them rather than a poor dev asking “how did this ever work!?”