I think there's a balance between the tokens
burned up rediscovering things vs tokens being
used keeping docs/decisions/skills/etc.
This mystical balance isn't difficult to measure. You don't have to believe anybody; just read the darn session transcripts. It's going to take at least one (but usually multiple) turns of grepping or other exploration to rediscover a thing. How many tokens does this add to your context? Since 1 token = ~4 characters you can count characters in your text editor.
Is this less, or greater than the number of tokens it would cost to simply add that thing to AGENTS.md?
If you're burning 5000 tokens to rediscover the same thing in every session, and it would take only 500 tokens to just put the thing in your AGENTS.md, it's an easy decision. Do you understand that paying 500 tokens in every session is less than paying 5000 tokens in every session?
If you're burning 5000 tokens to rediscover the same thing in 50% of your sessions, it's probably still worth it, but now you might consider placing it into a skill so that it only gets loaded into the 50% of sessions that need it.
If you're burning 5000 tokens to rediscover the same thing in 1% of your sessions then yeah, definitely skill. (You can add it to your prompts manually too, of course, but that is functionally equivalent to adding it to a skill that is set to manual invocation only...)
So I HEAVILY lean towards the former especially with
how effective I think it is these days.
How is this different from what I already said at the beginning of this conversation, where I recommended beginning with minimal (or no) skills or instructions... and then judiciously adding very lean ones based on actual observations? You claimed that this was a waste of time.