Thanks for the post. It is a complicated discussion but always looking to improve this area.

First to confirm... There should already be caching for deep search for all files except the .ino code? 

Deep search honours conditional #include statements. For example #ifdef TEST #include <foo.h> #endif

This means that #defines and compiler statements can affect which libraries are discovered. 

Deep search also discovers libraries included in other libraries. This means that if underlying library sources are updated without updating the project code, the previous search results become invalid.

The current level of cache should already avoid a lot of re-work during 2nd build, but we are looking at how we can take it up a level. Another alternative we are considering is to offer a higher level of cache along the lines you have suggested ++ alongside a manual menu item or button that will re-scan when a user knows external changes have been made.

There are also other items on our list for this, hopefully the next few months will see some more improvements.

If you believe the cache is not caching then please build and provide the information requested in yellow above.

Thanks