right, but i can tell Tycho that
Its not a problem for me that Tycho doesn't do that by default, as long as i can tell
<cacheOffline>true</cacheOffline>
[...]
I think you need to focus on the actual issue you face more than on a proposal of a solution. Your proposals do not fit well in the current design of Tycho.
So let's get back to the root issue: Tycho downloads p2 metadata although they are supposed to be available in cache already. Is that right? If so, then let's just try to improve Tycho on that matter: for example Tycho could just get the HTTP head first and ask for last-modified date before redownloading anything that's already cached. With that you only send a few requests without re-downloading anything.
Or you just make --offline work and then configure your CI to be --offline (use only cache) by default, and just run the job without this --offline from time to time when you know your .target has changed so the cache gets updated.
IMO. your concerns are not much different from the ones of many other projects, that have managed to deal with them. They may be a bit more evolved, but I have the impression that just improving what's already supposed to work in Tycho (p2 metadata cache, offline support) would be enough to cover your cases noticeably better.
