Tranche 6 — 15 of 17 raw sites in cron.go. Adds cron_jobs and
cron_executions to schema.sql and a full query set: job CRUD, owner
joins (via project and via service), execution list/insert/finish,
due-job scan for the scheduler, run bookkeeping, and retention trim.
The filtered list query and the sparse UPDATE builder stay raw — both
are genuinely dynamic. Go models keep string IDs; cronJobFrom and
cronExecutionFrom map uuid/null types at the boundary.
TestCronLiveInvariants covers insert/read, both owner joins, the
trigger read, execution lifecycle, retention trim, and delete on live
Postgres.
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Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
