# Custom Fields

## Objective

Let each workspace add the extra fields their process needs.

User-defined fields with stable IDs, typed validation, server-enforced visibility, and defined behaviour on type change and deletion.

## 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 field a stable internal ID that never changes, and treat the label as display-only. Renaming a field must not touch a single stored value — key data by ID, never by label.
2. Support a small, deliberate set of types: text, number, date, single-select, multi-select, checkbox, and user reference. Each type validates on the server; a client-side date picker is not validation.
3. Enforce per-field visibility and editability by role on the server, and apply the same rules to list views, exports, filters, and API responses — not just the record form.
4. Handle type changes explicitly: check every existing value against the new type first, show the user how many would fail, and refuse or quarantine rather than silently blanking them.
5. Do not let custom fields become an unbounded schema. Cap the field count per record type and reject deeply nested or free-form JSON values — an untyped bag of data cannot be validated, filtered, or exported reliably.

## 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

- Making a field required after records exist must not block editing every old record. Enforce it on new saves and report the backlog.
- Deleting a field needs a defined fate for its data: soft-delete and retain, or purge with an explicit warning and count.
- Removing an option from a select while records still use it must either keep it as a read-only legacy value or force reassignment.
- Exports and imports must round-trip custom fields by ID, so a re-import does not create duplicate fields with the same label.
- Filtering and sorting on custom fields needs indexing thought through; an unindexed value column turns every list query slow as the workspace grows.
- A user-reference field must handle the referenced user being deactivated or removed from the workspace.

## 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

- [ ] Values are stored against stable field IDs, and renaming a field loses no data.
- [ ] Every field type is validated on the server, not only in the form.
- [ ] Field-level visibility and edit permissions apply to forms, lists, filters, exports, and API responses.
- [ ] A type change reports how many existing values would fail before anything is written.
- [ ] Field deletion and select-option removal have documented, non-destructive-by-default behaviour.
- [ ] There is a cap on fields per record type and free-form nested values are rejected.
- [ ] 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.