# Customizable Dashboard Widgets

## Objective

Let people arrange the panels that matter to them.

A widget system with a catalog, add and remove, drag-to-arrange layout, and persisted per-user layouts that survive permission and data changes.

## 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. Define a widget contract — identifier, title, size constraints, required permissions, and configuration schema — and register every widget against it.
2. Give users a catalog to add from, removal, and rearranging, with the layout saved per user.
3. Persist layout per breakpoint, or persist one layout and define deterministic reflow rules for narrow screens. Do not save absolute positions and hope they still make sense on a phone.
4. Revalidate every widget on load against current permissions and data. A widget the user can no longer see must be removed or shown as unavailable, never rendered with someone else's numbers.
5. Put a ceiling on cost: cap concurrent expensive widgets, load them lazily below the fold, and give each one its own error boundary.
6. Do NOT implement metric computation, pre-aggregation, date ranges, or chart accessibility here — those are owned by Analytics Dashboard. Generic list and table preference storage is owned by Persistent View Preferences. Widgets consume those; they do not reimplement them.

## 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 widget removed from the catalog in a later release will still appear in saved layouts — handle the unknown identifier instead of crashing the dashboard.
- A widget whose underlying data source is deleted must degrade to an unavailable tile, not an error page.
- Overlapping or off-grid tiles after a resize must be reflowed deterministically; two users on the same layout must see the same result.
- One slow widget must not block the rest of the dashboard from rendering.
- Always offer a reset to the default layout — it is the only recovery when a saved layout is unusable.
- An empty dashboard needs a real empty state pointing at the catalog, not blank space.
- Layouts saved by one user and cloned to another must be re-validated against the second user's permissions before rendering.

## 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

- [ ] Users can add, remove, and rearrange widgets, and the layout persists across sessions and devices.
- [ ] Widget configuration is revalidated against current permissions and data on every load.
- [ ] No layout produces overlapping or unreachable widgets at any supported width.
- [ ] Expensive widgets are capped, lazily loaded, and individually error-bounded.
- [ ] A reset-to-default action exists and works from a broken layout.
- [ ] Metric computation and chart rendering are deferred to Analytics Dashboard.
- [ ] 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.