|Thanks for confirming my suspicions.
Obviously I got the compiler mixed up , so here is the way I view the whole mess.
To get from idea to running code I see these basic blocks
Operating system - with environment configuration
Development application (IDE )
Main file .*ino
"System " includes - example <stdio.h>
IDE "libraries" - example <LiquidCrystal.h>
Local includes - example "MyClass.h"
Compiler / linker (preprocessor)
I think I need to take a look how the compiler handles / finds the path to each include.
I can see if local includes are in SAME directory as the x.ino file it works fine.
But the "system" or "library" includes path are different and that why if fails.
But I want to write code and not troubleshoot the IDE.
Maybe I should use a different IDE.