Lately, I've been pondering this question in general and I'm worried the answer might be "Never" for some kinds of work - at least if we don't change how LLMs are currently developed and improved. At a high-level, the problem is they don't 'learn on the job' like a human and writing their memory & learning in .md files works for some things but fails for others.
While the 'rising tide' of baseline LLM knowledge continues to grow, they are still FTIs (Factory Trained Intelligences), meaning they mostly learn from data which can be assembled/tagged or synthesized in mass bulk - plus specific abilities in certain domains which the factory has prioritized for more costly special training. For some broad categories of important work, I suspect there's a significant unfilled gap in our LLM instances being able to effectively crystallize knowledge acquired on-task. Without that, context files will remain helpful crutches not true substitutes.