internal/datadir now owns the DATA_DIR mode as an exported constant,
DirPerm; internal/database consumes it in both places that create the
directory rather than keeping its own copy. datadir is the owner
because guarding and creating DATA_DIR is its whole purpose, and the
dependency runs the right way: datadir imports only the standard
library and the flock package, so database importing datadir adds no
cycle. A comment on DirPerm names it as the single source, chosen over
a source-scanning test because it survives refactoring and builds no
machinery that inspects the tree. The mode value is unchanged.
Model: opus-4-8
sneak