# Portal Host Registry

## Objective

Give floating interface elements a known, ordered place to render outside the layout flow.

A registry of named mount points for tooltips, menus, dialogs, and notifications, with a defined order and lifecycle.

## 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 small set of named hosts by purpose — one for tooltips, one for menus and popovers, one for dialogs and drawers, one for notifications — and have components ask for a host by name rather than reaching into the document themselves.
2. Guarantee exactly one host per name for the lifetime of the application, and make a second registration under the same name a loud failure rather than a silently duplicated mount point.
3. Make the first server-rendered pass safe: render nothing, or render inline, until the host exists, then attach. Any code that assumes a document node during the first render will break rendering on the server.
4. Mirror theme variables, colour scheme, text direction, and locale onto the hosts, because content mounted outside the application subtree does not inherit anything set on an ancestor inside it.
5. Do not implement focus trapping, stacking order, or dismissal here. Those belong to the Overlay Coordination Layer brief; this registry decides only where a surface is mounted and in what document order.

## 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

- The first render on the server happens before any host node exists. The component must produce valid output in that pass and attach afterwards, without a mismatch warning or a flash on hydration.
- Content rendered into a host sits outside the application's element tree and loses every inherited style variable, direction, and font setting. Without those mirrored onto the host, a dialog renders in the wrong theme on a page that is otherwise correct.
- Duplicate hosts appear when a module is loaded twice, when a development reload re-registers, or when the app is embedded twice on one page. Each duplicate silently swallows some surfaces and the bug looks intermittent.
- Events crossing a portal follow the component tree in the framework but the document tree natively, so outside-click detection written against native listeners will treat a click inside a menu as a click outside it.
- Unmounting a component must remove its portalled content. A dialog whose owner navigated away, leaving its markup behind in the host, is a stuck overlay with no way to close it.
- Hosts must be ordered in the document so notifications sit above dialogs and tooltips above both, since document order is the tiebreaker whenever stacking values are equal.
- When the app is embedded inside someone else's page, a generically named global host can collide with the host page's own. Scope the host identifiers to the application instance.

## 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

- [ ] All portalled content mounts into a named host obtained from the registry.
- [ ] Exactly one host exists per name, and a duplicate registration fails loudly.
- [ ] Server rendering completes without touching a host node and hydrates without mismatch or flash.
- [ ] Theme variables, colour scheme, text direction, and locale apply to portalled content identically to inline content.
- [ ] Unmounting an owning component removes its content from the host, leaving no orphaned markup.
- [ ] Hosts appear in a defined document order that puts notifications above dialogs and tooltips above both.
- [ ] Focus, stacking, and dismissal behaviour is delegated to the overlay coordination layer.
- [ ] 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.