# ZIP Download

## Objective

Let people select several files and download them as one archive.

A multi-select download that packages the chosen files and folders into a single archive.

## 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. Hang the action off the app's existing multi-select and Bulk Actions machinery. Users already know how to tick rows, and a separate selection mode for downloads will diverge from the rest of the list.
2. Re-check every file against the requesting user's permissions at build time, not only at selection time. Reuse the app's Secure File Downloads path for each member rather than reading from storage directly.
3. Show the total size and file count before the download starts, and let the user cancel a build that is still running.
4. Name the archive after what was selected and the date, so a folder of ten downloads is still navigable a week later.
5. Do not offer this as a way to export the entire account. That is a different feature with different expectations, and the app's Personal Data Export already covers 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

- Building the whole archive in memory before sending it will exhaust the process on a large selection and stall every other request on that worker. Stream entries out as they are read so memory stays flat regardless of selection size.
- Two files from different folders can share a filename, and the archive will end up with a silent duplicate or a truncated one. Preserve the folder structure inside the archive, and where a collision still occurs, disambiguate the name rather than dropping the file.
- Without a ceiling on total size and file count someone will select forty thousand files and hold a connection open for an hour. Set explicit limits, state them before the attempt, and explain what to deselect rather than failing at the end.
- An archive that takes minutes to assemble should not be built on the request. Move it to background work, then send the user a link when it is ready, with an expiry on that link and the same permission check on redemption.
- Non-Latin and accented filenames come back as replacement characters in some extraction tools. Write entry names in a Unicode-safe encoding and test with Cyrillic, Japanese, and accented Latin names before calling it done.
- A stream that fails midway produces a downloaded file that looks complete and opens corrupt. Detect the failure, avoid presenting a partial archive as finished, and let the user retry.
- A user who navigates away or loses connection mid-download must not leave a half-written temporary file behind on the server forever.
- An empty selection, or one where every file has since been deleted, must produce a clear message rather than an archive with nothing in it.

## 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

- [ ] Selecting several files and downloading produces one archive containing exactly those files.
- [ ] The archive is streamed and server memory does not scale with selection size.
- [ ] Folder structure is preserved inside the archive and filename collisions are disambiguated.
- [ ] Size and file-count limits are stated before the attempt and enforced.
- [ ] Long builds run in the background and deliver an expiring link that re-checks permissions.
- [ ] Non-Latin filenames extract correctly on common desktop tools.
- [ ] A failed build is reported rather than delivered as a truncated archive.
- [ ] 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.