# OAuth Token Refresh Recovery

## Objective

Keep connections alive when short-lived provider tokens expire.

A refresh lifecycle that renews access tokens safely under concurrency and stops cleanly when renewal is impossible.

## 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. Refresh proactively, shortly before expiry, rather than waiting for a 401. Also handle the 401 path — provider clocks and your clock disagree.
2. Serialize refresh per connection with a lock. Concurrent refreshes race, and with rotating refresh tokens the loser's token is already dead — the whole connection dies with it.
3. Write the new access token and any replacement refresh token in one atomic update. A crash between the two leaves the connection unrecoverable.
4. Classify refresh failures. A network error or 5xx is retryable with backoff; invalid_grant is permanent. Do NOT retry a permanent failure — it burns quota and never succeeds.
5. Notify the user only when a human must reauthorize. A transient refresh failure that self-heals must produce no notification at all.
6. The status surface and the reconnect button are owned by Integration Connection Health; set the state and let that feature render it.

## 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

- Some providers rotate the refresh token on every use and some do not. Handle both; assuming the wrong one silently breaks connections after the first refresh.
- A request that was in flight when the token expired must be retried once with the new token, not dropped.
- Background jobs and web requests may both hit expiry at once. The lock has to span processes, not just threads.
- A refresh token can expire from disuse. A dormant connection needs the same reauthorization path as a revoked one.
- Storing the new token must survive a failed write to the provider-facing side — never delete the old token until the replacement is committed.
- Repeated invalid_grant across many connections at once usually means a provider-side app change, not user error. Detect the pattern and alert operators before mass-emailing users.

## 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

- [ ] Tokens are refreshed before expiry, and expired-token responses are also handled.
- [ ] Concurrent refresh attempts for one connection are serialized and only one call reaches the provider.
- [ ] Access and rotating refresh tokens are persisted atomically.
- [ ] invalid_grant halts retries immediately; transient errors back off and retry.
- [ ] Users are notified only when reauthorization is genuinely required.
- [ ] A crash mid-refresh leaves the connection either on the old token or the new one, never on neither.
- [ ] 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.