# Staff Shift Schedule

## Objective

Show who is working when for the week, with coverage gaps visible at a glance.

A weekly grid of staff shifts with draft and published states and coverage warnings.

## 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. Build the minimum coherent version first: a week grid, shifts you can create and move, a draft state, and a publish action. Leave shift swapping, time-off requests, and labour-cost forecasting out until the grid is in daily use.
2. Keep an editable draft separate from what staff currently see, and change nothing for them until the week is published. A schedule that shifts under people as the manager thinks aloud is worse than a printed sheet.
3. Show coverage as a strip along the grid, comparing the people scheduled in each hour against a required level, so a gap is visible without reading every row.
4. Reuse the app's Recurring Schedule Builder for repeating shift patterns rather than adding a second recurrence engine, and reuse the existing notification channels for change notices instead of introducing a new one.
5. Do not store a shift as a day plus two clock times. Store real start and end instants with a zone, or overnight shifts and clock-change weeks will be wrong in ways nobody notices until someone is not there.

## 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

- Two shifts overlapping for the same person must be flagged at the moment of the edit, with both shifts named. Discovering the clash on the day means one of them goes uncovered.
- Hours below the required coverage level must be marked clearly on the grid, and the required level should be settable per day part rather than as a single number for the whole week.
- An overnight shift belongs to the day it started on and must be drawn as one continuous block spanning midnight, not as two fragments on separate days.
- Published shifts stay exactly as staff last saw them while a draft of the same week is edited, including through a partial or abandoned editing session.
- On publish, notify only the people whose own shifts actually changed, and tell them what changed. A broadcast to the whole team on every publish gets muted, including the week it mattered.
- A week that crosses a daylight-saving change contains a day of twenty-three or twenty-five hours. The grid must render it and shift durations must be computed from instants.
- Deleting or deactivating a staff member must not silently erase their published shifts; surface the resulting coverage gap instead.
- The grid must remain usable on a phone for someone checking their own shifts, even if editing stays a desktop task.

## 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

- [ ] A weekly grid shows every staff member's shifts with draft and published states kept separate.
- [ ] Overlapping shifts for one person are flagged during editing.
- [ ] Coverage below the required level is visible on the grid without opening each shift.
- [ ] Overnight shifts render as one continuous block on their starting day.
- [ ] Publishing notifies only the staff whose own shifts changed, and says what changed.
- [ ] Shift times are stored as instants with a zone and survive daylight-saving weeks.
- [ ] Repeating shift patterns use the app's existing recurrence builder.
- [ ] 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.