Answer
A few things worth trying, roughly in order: (1) reinstall the development-tools package to a fresh location, double-checking that the Build Home and Project Root paths entered during setup are actually correct; (2) make sure the chosen install location uses only plain folder names with no spaces or special characters, since some tooling relies on being able to navigate to these paths as literal URLs; (3) try a full Clean followed by a complete Rebuild of the solution, since some of these errors/warnings are transient and clear up after a clean rebuild; and (4) for whichever specific files the build errors mention as missing, navigate directly to those exact locations and confirm whether the files genuinely exist there — if they're truly missing, they sometimes need to be added back in manually.