# Component Deprecation Path

## Objective

Retire old components and props gradually instead of breaking every screen at once.

A defined route from marking a component or prop as obsolete to removing it, with warnings, replacements, and a dated milestone.

## 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. Mark the deprecation in all three places a developer might look: the static type layer, the component's documentation, and a development-time warning at the call site. A note in one place only will be missed by whoever is not reading that place.
2. Never deprecate without naming the replacement. State which component or prop takes over, and where the mapping is not mechanical, describe what the caller has to decide.
3. Where the change is mechanical, supply an automated rewrite so the migration is a single reviewed change rather than months of incidental edits. Where it is not, say so plainly rather than shipping a rewrite that produces plausible but wrong output.
4. Count remaining usages continuously and make the number visible, drawing on the record built by Component Inventory rather than maintaining a second list. Inventory owns the counting; this feature owns the lifecycle state attached to each entry.
5. Do not leave a deprecation open-ended. Attach a removal milestone at the moment of marking, because a deprecation with no end date is a permanent second implementation that everyone still copies from.

## 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 deprecation must appear in the types, the documentation, and a runtime warning together. A deprecated prop that only warns at runtime is invisible to anyone reading the documentation before they write the call.
- A replacement has to be named and a rewrite supplied where the mapping is mechanical. Telling callers a component is deprecated without saying what to use instead guarantees they keep using it.
- Remaining usage must be tracked as a live number rather than counted by hand at removal time, or the removal lands on a screen nobody knew still depended on it.
- A removal milestone must be a real date on a real release, and the deprecation must be reviewed when it arrives. Deprecations that slip indefinitely train everyone to ignore the warnings.
- Deprecation warnings must not fire in production for end users, and must not be so noisy in development that they drown the diagnostics developers actually need.
- Something consumed outside this codebase — an embed, a published package, a template — cannot be removed on the same schedule as an internal component, and needs its own longer window.
- The replacement must be in place and stable before the warning goes out, otherwise callers migrate onto something that is itself about to change.

## 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 deprecated component or prop is marked in the type layer, the documentation, and a development-time warning.
- [ ] Each deprecation names its replacement and provides an automated rewrite where the mapping is mechanical.
- [ ] Remaining usage counts are derived from the component inventory rather than a separate hand-maintained list.
- [ ] Each deprecation carries a removal milestone that is reviewed when it falls due.
- [ ] Deprecation warnings are absent from production builds and deduplicated in development.
- [ ] No component is removed while its usage count is above zero.
- [ ] 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.