find files via load commands within theory text; clarified Thy_Load.with_thy_text, simplified Thy_Load.check_thy;

clarified global get_recent_syntax: session always has its base_syntax, but it might be absent itself;

pass syntax through check_thy;

use Thy_Header.read on explicit text only -- potentially via File.read, not Scan.byte_reader; tuned signatures;

clarified Parse.path vs. Parse.explode -- prefer errors in proper transaction context;

tuned;

clarified bootstrapping of Pure;