# Maintenance Mode

## Objective

Pause the app on purpose instead of serving a generic 500.

An operator-controlled outage window that shows a real maintenance page, lets staff through, and tells API clients the truth.

## 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. Make the mode a runtime flag an operator can flip without a deploy, and store it somewhere that stays reachable when the database is the thing being maintained.
2. Allowlist bypass for authenticated staff and for the health check endpoint, so the people fixing the problem can still use the app and the load balancer does not remove every instance.
3. Return 503 with a Retry-After header for API and crawler requests, and render the maintenance page for browsers. A 200 on a maintenance page tells search engines your content is now an apology.
4. Support a read-only variant where GETs continue to work and writes are refused with a clear message, since most maintenance only needs writes stopped.
5. Do NOT let background jobs, webhook receivers, and scheduled tasks keep mutating data while the UI is blocked. Pause or queue them explicitly, or the maintenance did nothing.

## 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

- The maintenance page must render without hitting the database or any service that might be down — static assets, inline styles, no dynamic content.
- Let the operator set an expected end time and a short message; a page with no information generates more support load than the outage.
- In-flight requests when the flag flips should be allowed to finish rather than cut off mid-write.
- Webhook senders that get a 503 will retry; make sure the retry window is compatible with Retry-After or you will lose events.
- Turning maintenance off must take effect immediately across every instance, not on the next cache expiry or restart.
- Staff bypass must be identity-based, not a shared query-string token that leaks into logs and chat.

## 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

- [ ] An operator can enable and disable maintenance without deploying.
- [ ] Browsers get a maintenance page; API and crawler requests get 503 with Retry-After.
- [ ] Staff and health checks bypass the block.
- [ ] The page renders with the database unavailable.
- [ ] Background jobs and webhook processing are paused or queued during the window.
- [ ] Read-only mode is available and blocks writes with a clear message.
- [ ] 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.