I rebuilt Invoice Ninja's database from the SQL Schemity wrote, and the copy accepted a company key "probe-key " right next to an existing "probe-key".
The original refuses that. Its text columns use utf8mb4_unicode_ci, which ignores trailing spaces, so the two keys are duplicates. Our import read no collation from the mysqldump, so the copy fell back to MySQL 8's default, utf8mb4_0900_ai_ci, which counts the space. Same column, same unique key, a different rule.
Nothing failed. I only saw it because the test inserted rows and read them back instead of comparing column names.
Import now keeps every collation mysqldump writes.
commit 44676c3