Job dependencies (simple): only run if parent job succeeded recently

[csoscd]

Summary

Allow a job to declare a single parent job as a dependency. The job is skipped at execution time if the parent did not succeed within a configurable time window.

Motivation / Use Case

Common for sequential workflows: a "verify backup" job should only run if the preceding "create backup" job succeeded. Currently this requires external scripting or manual scheduling gaps.

Proposed Behaviour

• Each job can optionally specify one parent job and a "must have succeeded within N minutes" window
• At execution start, cron-wrapper.sh checks the parent's last execution result
• If the condition is not met, the job is skipped and recorded as "Skipped (dependency not met)" in the execution history (similar to the singleton-skipped status from issue Singleton guard: show 'skipped (singleton)' as distinct status in execution history #75)
• No change to the cron schedule itself — the dependency check is runtime, not schedule-level
• Circular dependency detection at save time (UI + agent validation)

Affected Component

• cron-wrapper.sh
• Agent
• Web UI

First Implementation Idea

1. Schema — add depends_on_job_id (nullable FK → cronjobs.id) and depends_on_max_age_minutes (int, default 60) to the cronjobs table; new migration file.
2. New agent endpoint — GET /crons/{id}/dependency-check returns {"satisfied": true/false, "reason": "..."} based on querying the most recent successful root execution (retry_attempt = 0, exit_code = 0) of the parent within the configured window.
3. cron-wrapper.sh — after the singleton check and before fetching the command, call the dependency-check endpoint. On satisfied: false, POST /execution/start + /execution/finish with exit code -7 ("Skipped – dependency not met") and exit.
4. CronGetEndpoint — include depends_on_job_id and depends_on_max_age_minutes in the job payload.
5. Web UI — job form gains a "Depends on" dropdown (job selector) and a "within N minutes" input; only shown when a parent is selected. Circular dependency validated on save.