Add Queue.HasActiveRun to detect overlapping executions

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Business impact

A job whose execution regularly takes longer than its own cron interval (a slow every-minute job that sometimes takes 90 seconds) will, today, happily pile up overlapping executions of itself: the materializer creates a new due occurrence on schedule regardless of whether the previous one has finished. For a job that isn't safely re-entrant on the target side, this means concurrent duplicate work against the same downstream system exactly when it's already under load -- the worst possible time to pile on more concurrent requests to it.

Problem

pkg/queue.Queue has no way to answer "does this job currently have a run in progress?" HasActiveRun is a placeholder that panics with "TODO(ticket-E5): HasActiveRun not implemented".

Current behavior

Calling HasActiveRun for any job, including one with no runs at all, panics instead of returning a boolean.

Expected behavior

Queue.HasActiveRun(ctx, jobID) returns whether the given job currently has any job_runs row in 'leased' or 'running' status. This is the building block a cron materializer could eventually use to skip creating a new occurrence while the previous one is still in flight.

Steps to reproduce

Call queue.HasActiveRun(ctx, jobID) for a job with no runs at all.
Observe: a panic, "TODO(ticket-E5): HasActiveRun not implemented", instead of (false, nil).

Why this matters

This is a simple existence check (EXISTS (SELECT 1 FROM job_runs WHERE job_id = $1 AND status IN ('leased', 'running'))), but it's the prerequisite for a meaningful "skip if still running" policy -- without it, there's no way to even ask the question.

Suggested approach

Look at how other pkg/queue methods query job_runs by job_id and by status (e.g. ListByJob, ReclaimExpiredLeases's WHERE status IN (...)) for the patterns to combine here.

Acceptance criteria

HasActiveRun returns false for a job with no runs at all
HasActiveRun returns true for a job with at least one run in 'running' or 'leased' status
HasActiveRun returns false for a job whose only runs are 'succeeded', 'failed', or 'dead'
go build ./..., go vet ./..., gofmt -l . stay clean

Verification

TEST_DATABASE_URL="postgresql://chronos:chronos@localhost:5432/chronos?sslmode=disable" go test ./tickets/tests/... -run TestTicket14 -v

Hints (0/2)

Try it without hints first — the reading is the exercise.

Working on this ticket

Work on a branch named for the ticket — that's what you'll submit.

Branch off your fork

$git checkout -b feat/has-active-run

Fix it and commit

Meet every acceptance criterion, and add a test that would have caught this.

Push the branch

$git push -u origin feat/has-active-run

Submit it below

Paste your fork URL and the branch name, with a short write-up of the root cause.

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Questions

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The project

Chronos — Distributed Cron Scheduler

A "cron-as-a-service" job scheduler backed entirely by Postgres -- SKIP LOCKED leasing and advisory-lock leader election, no etcd/ZooKeeper/Consul -- twenty ways the coordination quietly breaks.

Fork on GitHub

Download

Setup

Chronos — Distributed Cron Scheduler

git clone <your-fork>
cd GolangDevTraining/chronos
docker compose up --build   # postgres + two app replicas + adminer, hot-reloading on save

Two replicas run on () and (), both against the same database; Adminer is at . Verify with and .