uk_sys_menu_app_seed_code_del covers (app_code, seed_code, deleted_at) and is
created by 1786700008000 with explicit SQL. The struct tag named the same
index on SeedCode alone, and a named uniqueIndex tag collects only the fields
carrying that name - so AutoMigrate on this model would build a unique index
on seed_code by itself: stricter than the real one, and forbidding two
applications from both having a "dir" node, which the composite key exists to
allow.
Worse than being stricter, it would win. The migration only creates its index
when HasIndex says the name is free, so a schema built by AutoMigrate first
keeps the wrong index and the migration steps over it without a word.
The tag cannot express the real index: deleted_at comes from the ModelTime
embed shared by every table, which no single model can add a tag to. So the
tag goes and the migration is the only thing that creates it.
No database is affected. The initial table migration AutoMigrates a frozen
snapshot of this model that has neither app_code nor seed_code, and nothing
else in the repository AutoMigrates the live one - which is why this stayed
invisible until a test built the schema from the live model and seeded two
applications, and got a unique-constraint failure on a seed code they are
supposed to be able to share.
