# Local UI State Conventions

## Objective

Settle where each kind of interface state lives before it ends up everywhere.

A written rule for which state belongs to a component, to the URL, to storage, or to the account.

## 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. Classify the app's existing interface state into four homes and write the rule down: ephemeral and component-local, shareable and therefore in the URL, device-specific and therefore in storage, or account-level and therefore on the server.
2. Put anything a user would expect to survive being sent as a link into the URL — the active tab, the open record, filters, sort, the search term — and read it from there rather than mirroring it into a second copy that can drift.
3. Keep the rest as close to the component that owns it as it will go. A menu's open state, a hovered row, a tooltip, and a half-typed inline edit have no business above the element they belong to.
4. Promote a piece of state only when a second consumer genuinely needs it, and record why. Lifting state in anticipation of a future need is how a global store fills with things one component reads.
5. Persistence of sort, columns, filters, and layout across sessions belongs to the app's existing view preferences feature; this entry decides where transient state lives while a screen is open. Do not build a second persistence path 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

- State declared far above its only consumer re-renders everything in between for no reason, and makes the component impossible to reuse or test on its own. Move it down until it sits with the thing that owns it.
- Promotion should be the exception and needs a stated reason. Once a value is global, every component may read it, and the cost of removing it later is proportional to how many did.
- A route change, a workspace switch, or a change of signed-in user must clear the state that belonged to the old context — an open menu, a filter, a draft comment, a selected row. Carrying a previous workspace's selection into a new one is a data leak, not a convenience.
- Ephemeral state must not be persisted. A restored scroll position, a reopened dropdown, or a resurrected half-typed search on the next visit is confusing rather than helpful.
- Two tabs open on the same account share device storage, so anything written there must tolerate the other tab writing it too, or the tabs will overwrite each other.
- Anything held in the URL becomes part of a link the user may paste into a chat, so it must not carry record contents, tokens, or personal data.
- Drafts are the genuine exception to the persistence rule, and they need an explicit owner, a scope, and a point at which they expire — not a blanket permission to persist everything.

## 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 category of interface state has a documented home: component, URL, device storage, or account.
- [ ] Shareable state is read from the URL, with no duplicate copy held elsewhere.
- [ ] Component-local state sits at the element that owns it, not above it.
- [ ] Each promoted piece of state has a second consumer and a recorded reason.
- [ ] Route, workspace, and identity changes reset the state belonging to the previous context.
- [ ] No ephemeral state survives a reload, apart from drafts, which have a defined scope and expiry.
- [ ] Cross-session persistence of view settings is delegated to the existing view preferences feature.
- [ ] 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.