The seed handler computed seeded from a pre-flight SELECT then returned
seeded:!alreadySet. Under a genuine concurrent race both requests can
SELECT the empty table, both enter the insert branch, and both return
seeded:true though only one row was actually written. Replace the
SELECT + conditional onDuplicateKeyUpdate with a single INSERT IGNORE
and derive seeded from affectedRows (1 = inserted, 0 = ignored/existing
row preserved, D-03). On MariaDB onDuplicateKeyUpdate(value=value)
reports affectedRows 1 for both insert and no-op, so it cannot
distinguish them; INSERT IGNORE can. timezone is bound via a
parameterized sql template and is already IANA-validated by zod. Adds a
test asserting seeded:false for a directly-pre-inserted row.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
