# Conditional Form Fields

## Objective

Show only the fields that matter based on what the user already answered.

Form fields that appear, disappear, and become required depending on other answers, with the server agreeing about which branch is live.

## 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. Find the forms with fields that only apply in some cases and define, per field, the exact condition that shows it.
2. Write down one explicit rule for hidden values: cleared, preserved, or ignored. Apply it consistently — silent submission of a value the user can no longer see is the classic bug here.
3. Make 'required' conditional too. A hidden field must never block submission, and a revealed field must be validated.
4. Mirror the same branch logic on the server. The client decides what to show; the server decides what is valid.
5. Do NOT use display:none alone to hide a field. A visually hidden input is still focusable, still submitted, and still read by screen readers — remove it or disable it properly.

## 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

- Editing an existing record must reopen the branch that record was saved with, including nested conditions.
- Revealed fields must be announced to assistive technology without yanking focus away from the control the user just used.
- A chain of conditions must collapse cleanly — hiding a parent must hide and resolve everything under it.
- Layout must not jump when a field appears; reserve space or animate the height.
- A server validation error on a hidden field must reopen the branch containing it rather than showing an error nobody can find.
- Autosave and draft restore must record which branch was active, not just the field values.

## 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

- [ ] Each conditional field has a stated rule for what happens to its value when hidden.
- [ ] Hidden fields are never submitted, never required, and never focusable.
- [ ] The server applies the same branch logic as the client.
- [ ] Editing an existing record restores the correct branch.
- [ ] Newly revealed fields are announced and do not steal focus.
- [ ] Errors on fields inside a collapsed branch reveal that branch.
- [ ] 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.