# Keyboard Interaction Primitives

## Objective

Give every menu, list, and dialog the same keyboard behaviour instead of ad hoc handlers.

A shared set of keyboard behaviours for activation, dismissal, roving movement, and typeahead, adopted by the app's existing interactive components.

## 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. Inventory every component in the app that already listens for key presses — menus, comboboxes, tab strips, trees, dialogs, table rows, date pickers — and record which keys each one currently handles and how they disagree.
2. Settle on one behaviour per pattern: Enter and Space activate, Escape dismisses the nearest layer, arrow keys move within a group, Home and End jump to the ends, and printable characters start a typeahead that resets after a short idle period.
3. Move focus with a single roving tabstop per group so the whole group is one tab stop from outside, and make the currently focused item the only one reachable by Tab.
4. Route dismissal through a layer stack so Escape closes the topmost thing only — a popover inside a dialog inside a fullscreen view must unwind one layer at a time.
5. Do not reimplement behaviour the browser already provides on native controls. Re-binding arrow keys on a real select, textarea, or link steals behaviour users rely on and usually breaks assistive technology; the announcement side of these interactions belongs to Live Region Manager, not 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

- Native elements come with keyboard behaviour already — links, buttons, selects, radio groups, and text inputs must keep it, so the primitives have to detect a native target and stand aside rather than intercept.
- Input Method Editors compose characters over several key presses, and acting on Enter or Escape mid-composition destroys the word being typed; suppress activation and dismissal while a composition is in progress.
- Platform shortcuts collide with anything the app claims — Command and Control combinations, browser find, and screen reader pass-through modes — so single unmodified keys are safer than combinations, and anything that overlaps a system binding must be dropped.
- Interactive elements nest: a menu item containing a delete button, a table row containing a link. Decide which level owns the key press, stop propagation deliberately, and make sure the inner control is reachable without breaking the outer group's arrow movement.
- Typeahead must not fire while focus is inside a text field, or typing a search term will jump the selection somewhere unexpected.
- A group whose items are virtualized cannot move focus to an element that is not rendered; scroll the target into existence first, then focus it.
- Disabled and hidden items must be skipped by arrow movement rather than focused and silently ignored, which strands the user pressing the same key repeatedly.

## 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 interactive group in the app responds to Enter, Space, Escape, arrows, Home, and End the same way.
- [ ] Each group is a single tab stop from outside, with a roving tabstop inside it.
- [ ] Escape closes only the topmost layer, and nested layers unwind one press at a time.
- [ ] No key handler fires during text composition or while focus sits in a text field, except the field's own behaviour.
- [ ] Native controls retain their browser-provided keyboard behaviour unmodified.
- [ ] Arrow movement skips disabled and hidden items and works in virtualized lists.
- [ ] 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.