Background Job

Background Job Playbook

HARD-GATE

• Idempotency key and error classification are documented before implementation.
• A failing worker test exists and fails for the right reason before perform/1 is written.
• perform/1 is a thin edge: fetch IDs → pure core → return tagged tuple.
• Failure paths are tested; user approves the worker design.
• mix format --check-formatted, mix credo --strict, and the full mix test suite are green before the PR is opened.

When to use

Adding or hardening Oban (or similar) background workers.

Atomic skills this playbook loads

Flow

flowchart TD
  A[Idempotency + error classes] --> B[Failing perform test]
  B --> C[HITL: approve worker design]
  C --> D[Thin perform/1 + context]
  D --> E[Retry discard unique tests]
  E --> F[Telemetry optional]

Agent Phases

Phase 1 — Design

Document: queue, args (IDs only), idempotency key, transient vs permanent errors.

HARD GATE — Idempotency and error classification:

• Queue, args (IDs only), idempotency key, and error classes are documented.
• Transient vs permanent errors are classified.

If gate fails: Revisit the design doc; do not write perform/1 until the contract is clear.

Phase 2 — RED

Worker test expecting success/cancel/error paths; must fail until implemented.

HARD GATE — Failing worker test:

• A worker test exists for success, cancel, and error paths.
• The test fails for the right reason before perform/1 is written.

If gate fails: Adjust the test so it exercises missing behaviour, not a syntax/config mistake.

Phase 3 — HITL impl

1. Propose perform/1 as edge: fetch → domain → tuple.
2. HUMAN-IN-THE-LOOP: approve.
3. Implement; enqueue from context, not LiveView.

HARD GATE — Thin perform/1:

• perform/1 fetches IDs, delegates to a pure core/domain function, and returns a tagged tuple.
• User approves the worker design before implementation.
• Enqueue happens from context, not LiveView.

If gate fails: Extract logic into a context or pure function; re-HITL the design.

Phase 4 — Failure paths

Cover: not found → cancel; transient → error/retry; duplicate → unique.

HARD GATE — Failure paths tested:

• not_found path returns {:cancel, _} or equivalent.
• Transient errors are retried; permanent errors are discarded.
• Duplicate jobs are handled via unique options or idempotency key.

If gate fails: Add missing tests and handling for each failure class.

Phase 5 — Monitor

Attach telemetry/logging for failures if production-bound.

HARD GATE — User approval and green suite:

• User approves the final worker design.
• mix format --check-formatted, mix credo --strict, and mix test pass.
• Telemetry/logging is attached for production failures.

If gate fails: Fix formatting, Credo, or test failures; re-HITL if the design changed.

Verification checklist

• Idempotency plan
• Tests for success and failure classes
• HITL approval
• No large payloads in args
• Enqueue from context

Error Recovery

Non-idempotent side effects → add guards/unique; re-test double perform.

Output Style

## Background Job Report

**Design:** <queue, args, idempotency key, error classes>
**Test command:** `<mix test command>`
**HARD-GATE results:**
- Idempotency and error classification: PASS / FAIL
- Failing worker test: PASS / FAIL
- Thin perform/1: PASS / FAIL
- Failure paths tested: PASS / FAIL
- User approval and green suite: PASS / FAIL
**Verdict:** APPROVE / REQUEST_CHANGES