Yeah, the context window is a blunt instrument, everything competes for attention. I get better luck with shorter, more opinionated skills that front-load the key constraints vs. comprehensive docs that get diluted. Also explicitly invoking them (use the X skill) seems to help vs hoping they get picked up automatically

Yes, unfortunately the most reliable way is to inject them into the user prompt at a fresh session. My guess is that biasing towards checking for the tools availability too much affects performance, which might explain why it is quite rarer that I see it just choose to use a skill without previous prompting.