[dajiaohuang]

Summary

• Reject zero, negative, and fractional --batch-size values before table lookup or database access.
• Prevent zero-size arithmetic failure and negative-size non-progressing fill loops.
• Add focused tests for invalid and valid batch sizes without a database.

Validation

• ruby -I lib test/fill_validation_test.rb — 2 runs, 9 assertions, passed (Ruby 3.4.12; task-local gems).
• The full suite was not run because the project suite requires a PostgreSQL database; no database was used for this change.

[ankane]

Thanks @dajiaohuang