A definition is identified by role.type and named role.type.lang
(package.lang for packages). Code blocks declare it via role= on the
info string; real files by their filename. Blocks and files without a
matching role.type are ignored. file= still overrides the auto-name.
Relative asset and $variants paths now resolve against the markdown
file's directory (baseDir) rather than the virtual name. Same role.type
with different ids groups under one name; duplicate type#id still
errors. Migrate fixtures and example games to role=.