It's very common, but (like most things with LLMs) it's not as deterministic as you might imagine. A common technique for agents is to have them create a "handoff" document (usually markdown) that summarizes the previous session-- goals, important files/links, etc. There are dozens of proprietary ways of doing this, and Claude Code automates the process with its /compact command and even does auto-compaction as you reach your context limit. ChatGPT has been doing autocompaction since the beginning as it started out with a comically small context window.