# Background Job Progress

## Objective

Show people what a long import, export, or report is actually doing.

Durable progress for long-running work, with distinct states, live updates, and a real failure path.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Persist job state server-side: status, progress, counts, started and finished times, and the requesting user.
2. Model the states explicitly — queued, running, stalled, cancelled, failed, completed — and give each its own copy. A single spinner cannot express any of that.
3. Push updates to the client where you can, and fall back to polling with a widening interval. Progress must survive a refresh, a closed tab, and a different device.
4. Let the user cancel a running job, and make cancellation actually stop the work rather than just hiding the row.
5. Do NOT show a percentage you cannot compute. An honest 'processed 4,120 of 50,000 rows' beats a fabricated bar that sits at 90 percent.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- A job with no heartbeat for a defined period is stalled, not running. Say so and offer retry.
- Launching the same job twice must be blocked while one is in flight, with a clear reason.
- A job that completes after the user lost access to the source data must not deliver its output.
- Retry must be safe to press twice. Partial work already committed should not be duplicated.
- Error details must be actionable for the user — which row, which field — without exposing stack traces or internal identifiers.
- Completed job artefacts need a retention policy and expiring download links.
- A queue backlog must be visible as queued, not as a running job stuck at zero percent.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Job state is persisted and reloads correctly after a refresh or on another device.
- [ ] Queued, running, stalled, cancelled, failed, and completed are distinguishable in the UI.
- [ ] Progress reflects real measured work, or shows counts instead of a fake percentage.
- [ ] Duplicate submissions of the same job are prevented while one is in flight.
- [ ] Cancellation stops the work, not just the display.
- [ ] Failures offer retry and user-readable error detail with no stack traces.
- [ ] Generated files expire on a defined schedule.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.