Release v19.59.7

Changed

• On startup the SQL storage upgrades existing per-event-source constraint tables to a unique index. On SQL Server the value column is bounded to 200 characters first; the change is skipped, never truncating data, when a table holds longer values or values stored before constraint values were hashed, and a warning names the table and links to #4866. A table that already contains duplicate values keeps every row, keeps a non-unique index and logs a warning once per process; remove the duplicates and restart to get the unique index. (part of #3744)

Fixed

• Unique constraints on SQL storage are now settled by the database: two concurrent appends claiming the same value no longer both succeed. Per-event-source constraint tables get a unique index on the value on PostgreSQL, SQL Server and SQLite, and a collision is reported as a constraint violation instead of leaving two holders. (#3744)
• On SQL storage, moving a claim to a value another event source already holds is rejected and keeps the original claim, instead of losing it. (part of #3744)