Bounded read (cap+1 byte tells 'at the limit' from 'over'); a file that fails
validation creates no row; a prober fault is our error, not the user's bad
file; a row whose job cannot be submitted is failed, never left queued.
Mutation-checked: cap off-by-one, missing cleanup and deleting the handed-over
file each turn a test red.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
mathiasandClaude Sonnet 5.5