# Audio Chapter Markers

## Objective

Break a long recording into named chapters listeners can see and jump between.

Named, timestamped chapters on long audio or video, shown in a list and on the scrubber, each addressable by its own link.

## 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. Store chapters as an ordered list of start times and titles attached to the existing media record, and render them both as a list beside the player and as markers on the scrubber.
2. Let an author add, rename, reorder by moving start times, and delete chapters in the player itself, with the current playback position offered as the default start time for a new chapter.
3. If chapters are generated automatically, treat the generated set as a first draft. The author's edits must win and must survive the next generation run.
4. Make each chapter linkable through the app's existing shareable deep link mechanism, so opening the link starts playback at that chapter rather than at the beginning.
5. Do not build a separate chapter editing screen away from the player. Editing a boundary without hearing what is at that boundary produces chapters that start one sentence late.

## 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

- Authors must be able to override both generated titles and generated boundaries. Automatic segmentation reliably names a chapter after the first thing said in it, which is often the end of the previous topic.
- Chapters only a few seconds long turn the scrubber into a picket fence. Enforce a minimum duration, and either merge or refuse to display markers that would collide at the current scrubber width.
- Re-encoding or trimming the media invalidates absolute marker positions. Detect that the source duration changed, and either remap the markers or flag them as needing review rather than silently seeking to the wrong place.
- Each chapter needs a deep link that starts playback at that point, and that link must still land somewhere sensible if the chapter has since been deleted.
- A recording with a single chapter should render as an ordinary recording with no chapter list, not as a list with one entry and an empty scrubber.
- Chapter titles travel further than the player: they land in the episode description and in any feed the audio is syndicated to, where the app cannot edit them afterwards. Limit their length so they do not overflow the scrubber, and screen them before the recording is published.
- A chapter start time beyond the end of the media, or two chapters starting at the same second, must be rejected at save time with a clear message.
- The chapter list must be keyboard navigable and announce the current chapter, and marker positions must not be the only indication of where a chapter begins.

## 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

- [ ] Chapters appear as a list beside the player and as markers on the scrubber.
- [ ] Authors can add, rename, and delete chapters from the player, with the current position as the default start.
- [ ] Author edits survive a regeneration of automatic chapters.
- [ ] Each chapter has a deep link that starts playback at its start time.
- [ ] Chapters below the minimum duration are prevented, and overlapping or out-of-range start times are rejected on save.
- [ ] A single-chapter recording renders without chapter chrome.
- [ ] The chapter list is keyboard navigable and announces the active chapter.
- [ ] 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.