# Document Watermarking

## Objective

Stamp a draft, confidential, or recipient mark onto documents as they are downloaded.

A server-side watermarking stage applied to generated and stored documents on their way to a reader.

## 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. Apply the mark on the server as the file is generated or served. A watermark drawn in the browser or laid over a preview is gone the moment somebody requests the raw file, which defeats the entire point.
2. Extend the app's existing PDF Export path rather than adding a second document pipeline. The watermark is a stage in the export, not a separate feature with its own renderer and its own fonts.
3. Make the mark legible without obscuring the content: a diagonal or footer mark at reduced opacity, sized against the page rather than a fixed number of points.
4. Support a recipient-identifying mark for documents that need leak tracing, carrying the reader's name or account and the time the copy was served.
5. Keep the clean original and the watermarked copy at separate storage paths with separate access rules, and never let a request for one return the other.

## 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 mark drawn in the viewer is not a watermark. If the client composites it, the reader can request the underlying file directly and get a clean copy.
- A mark heavy enough to be unmissable is usually heavy enough to make small print unreadable. Tune opacity and size so the document is still usable at normal reading zoom.
- One file can hold pages of different sizes and rotations. Position and rotate the mark from each page's own box, or landscape and rotated pages get a mark running off the edge.
- When the mark identifies a recipient, the marked copy becomes personal data in its own right. Decide how long those copies are kept and who besides the recipient may read them back.
- Clean and watermarked copies must not share a cache key or a predictable filename. A shared key will eventually serve the unmarked file to someone entitled only to the marked one.
- Regenerating the same document for the same recipient must produce the same mark, or a leaked copy cannot be traced back to a single download.
- A document whose pages are scanned images needs the mark composited into the image layer. A text layer added over a flat scan may never render at all.
- Exporting an already-watermarked document through the same path must not stamp it twice.

## 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 document served through the export path carries the configured mark.
- [ ] The mark is applied server-side and is present in the raw downloaded file.
- [ ] Pages of differing size and rotation each carry a correctly placed mark.
- [ ] Body text stays readable at normal zoom with the mark applied.
- [ ] Recipient-marked copies record who they were issued to and when.
- [ ] Clean originals are stored apart from marked copies and are unreachable by a reader entitled only to the marked one.
- [ ] 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.