# Search Match Highlighting

## Objective

Show users why each result matched instead of making them hunt.

Highlighted spans in search results marking the text that matched the query, rendered safely.

## 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. Escape the record text first, then insert highlight markup. Escaping afterwards destroys your own markup, and skipping it gives you stored XSS.
2. Escape the query too before using it to match. A raw user query containing regex metacharacters will either throw or match the wrong thing.
3. Match case-insensitively but render the original casing from the source text — never the casing the user typed.
4. For long fields, truncate around the first match rather than from the start, so the snippet actually contains the highlighted term.
5. Do NOT highlight every occurrence in a long body. Cap the number of highlighted spans per snippet; a page of yellow is unreadable.

## 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

- Overlapping and adjacent matches must merge into one span, not nest into broken markup.
- The query may match in a field that is not displayed. Either show that field's snippet or do not claim a match.
- Highlight markup must be decorative to assistive tech — do not make a screen reader announce a mark on every word.
- Accented and multi-byte characters must not be split mid-character by truncation.
- When the match came from a synonym or stem, the literal query string is absent; highlight the term that actually matched.
- Truncation must show that text was cut, and must not cut in the middle of a highlighted span.

## 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

- [ ] Result text is escaped before highlight markup is inserted.
- [ ] Queries containing regex or HTML characters neither throw nor render as markup.
- [ ] Matching is case-insensitive and the original casing is preserved.
- [ ] Long fields truncate around the match, with an ellipsis indicating the cut.
- [ ] Overlapping matches merge into a single span.
- [ ] Screen readers do not announce the highlighting as separate content.
- [ ] 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.