# Dropdown Menu Primitive

## Objective

Give every action menu in the app the same keyboard, pointer, and dismissal behaviour.

A reusable menu primitive covering triggering, item navigation, selection, disabled items, and closing.

## 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 every action menu in the app — row overflow menus, account menus, bulk-action menus, toolbar menus — and rebuild them on one primitive so they stop behaving differently from each other.
2. Implement the full keyboard model: arrows move between items, Home and End jump to the ends, typing letters jumps to the matching item, Enter and Space activate, and Escape closes and returns focus to the trigger.
3. Close on outside pointer press, on Escape, and on the trigger being pressed again, and always return focus to the trigger so the user is not dropped at the top of the document.
4. Render items as a single menu semantic with roles that match their behaviour, distinguishing plain actions from checkable and radio-style items, so a screen reader announces state rather than just labels.
5. Anchoring, flipping, and viewport clamping belong to the Popover Positioning Engine, and focus containment while the menu is open belongs to the Focus Containment Primitive. Consume both rather than reimplementing either here.

## 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

- Arrow navigation must wrap at both ends, Home and End must reach the first and last enabled items, typing must match on the item's visible text with a short buffer that resets after a pause, and Escape must close only the innermost open menu.
- Disabled items must remain visible and announced as disabled so the user understands the action exists, but must be skipped by arrow navigation and typeahead and must not activate on click.
- Submenus open on hover with a delay and on right-arrow from the keyboard, and must tolerate the pointer travelling diagonally across a neighbouring item on the way — closing the submenu the instant the pointer leaves the parent item makes it almost unusable.
- Not every menu should close on selection. A checkbox item that toggles a column stays open so the user can toggle several; a navigation item closes immediately. Decide per item type rather than closing unconditionally.
- A menu whose items exceed the available height must scroll internally while keeping keyboard navigation scrolling the focused item into view.
- Items the current user has no permission to invoke must be absent or disabled with a reason, never present and failing on click.
- A destructive item needs visual separation from the ordinary ones, so a mis-aimed arrow key does not land on Delete beside Duplicate.

## 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 action menu in the app is built on the one primitive.
- [ ] Arrows, Home, End, typeahead, Enter, Space, and Escape all work in every menu.
- [ ] Disabled items are announced, skipped by navigation, and cannot be activated.
- [ ] Submenus open by pointer and by keyboard and survive diagonal pointer movement.
- [ ] Menus close on outside press, Escape, and re-trigger, and focus returns to the trigger.
- [ ] Whether an item closes the menu is defined by its type, not applied uniformly.
- [ ] Positioning and focus containment are delegated to the shared primitives.
- [ ] 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.