# Upload Malware Scanning

## Objective

Quarantine uploaded files until they are known safe.

A quarantine lifecycle for uploads: every new file is unreachable until scanned, with defined handling for scanner failures and infected results.

## 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. Give every upload an explicit scan state — pending, clean, infected, or error — and default it to pending the moment the bytes land.
2. Make pending and infected files unreachable from every access path in the app, including admin views, previews, thumbnails, and any signed URL. A quarantine with one exception is not a quarantine.
3. Scan asynchronously and update the state; do not block the upload request on the scanner.
4. Decide and document what an infected file does: delete immediately, or retain for a fixed period for investigation. Both are defensible; an undefined policy is not.
5. Tell the user their file was rejected in plain language. Do NOT surface the signature name, the scanner's raw output, or any internal file path — that hands an attacker a feedback loop for tuning their payload.
6. Signed-URL issuance and download authorization are owned by Secure File Downloads. Extend that feature to consult scan state rather than building a parallel delivery path here.

## 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 scanner timeout or outage must fail closed — the file stays pending and inaccessible, and the backlog is retried and alerted on.
- Files larger than the scanner's limit need an explicit decision, not a silent pass.
- Archives can hide payloads several layers deep, and zip bombs expand catastrophically. Cap recursion depth and expansion ratio.
- A file already marked clean can become infected as signatures update. Support re-scanning existing storage.
- False positives need a human review path, or you will permanently delete a customer's legitimate file.
- A URL signed while a file was clean must stop working the moment it is marked infected.
- Uploads that never complete scanning must not accumulate as permanent pending clutter — expire them.

## 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

- [ ] Every uploaded file has a scan state and starts as pending.
- [ ] Pending and infected files return no bytes from any route, signed or otherwise.
- [ ] Scanner outages and timeouts leave files inaccessible rather than passing them through.
- [ ] The infected-file retention or deletion policy is written down and implemented.
- [ ] User-facing rejection messages contain no signature names or internal paths.
- [ ] A previously clean file can be re-scanned and revoked.
- [ ] 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.