## Context

Currently, the frontend displays raw UUIDs for user references:
- Task list shows `assigneeId` (e.g., "a1b2c3d4-e5f6...") or "Unassigned"
- Task detail shows `assigneeId` and `createdById` 
- Shift detail shows `memberId` for each signup

The backend already stores `DisplayName` in the `Member` entity but the API DTOs don't expose it. The `ShiftService` already demonstrates the pattern of joining with Members (lines 82-87), which we can replicate for Tasks.

## Goals / Non-Goals

**Goals:**
- Add member name fields to backend DTOs
- Update TaskService to query and include member names
- Update ShiftService to include member name in ShiftSignupDto
- Update frontend TypeScript interfaces
- Replace UUID displays with names in task/shift UIs

**Non-Goals:**
- No database schema changes
- No changes to authentication or authorization
- No changes to how tasks/shifts are created or updated
- No caching layer for member names

## Decisions

### 1. Add names to existing DTOs vs create new DTOs
**Decision:** Add optional fields to existing DTOs

**Rationale:**
- Keeps API surface simple
- Backward compatible - existing clients ignore new fields
- No breaking changes to existing integrations

**Alternative considered:** Create new DTO versions (e.g., `TaskDetailDtoV2`)
- Rejected: Unnecessary complexity for a simple additive change

### 2. Fetch member names via JOIN vs separate query
**Decision:** Use JOIN in TaskService methods

**Rationale:**
- More efficient - single query per endpoint
- Pattern already exists in ShiftService
- Avoids N+1 query problem

**Alternative considered:** Query members separately and build lookup dictionary
- Rejected: Adds complexity and extra database round-trips

### 3. Handle missing members (orphaned IDs)
**Decision:** Return null for name when member not found

**Rationale:**
- Data integrity issue should surface visibly
- Frontend can display fallback like "Unknown" or keep showing ID
- Logging can track data inconsistencies

### 4. Frontend handling of null names
**Decision:** Frontend shows fallback text when name is null

**Implementation:**
```typescript
// Task list
task.assigneeName || 'Unassigned'

// Task detail
task.assigneeName || 'Unassigned'
task.createdByName || 'Unknown'

// Shift signups
signup.memberName || 'Unknown Member'
```

## Risks / Trade-offs

| Risk | Mitigation |
|------|-----------|
| JOIN adds query complexity | Keep JOINs simple, only on indexed columns (Member.Id) |
| Larger API response payloads | Minimal impact - names are small strings |
| Member names become stale | Acceptable - names rarely change; eventual consistency |
| Database performance degradation | Monitor query execution plans; add caching if needed |
| Partial data on member deletion | Show "Unknown" fallback; log orphaned references |

## Migration Plan

1. **Backend DTO changes** - Add new optional fields
2. **Backend service changes** - Update queries to include names
3. **Frontend type updates** - Add name fields to interfaces
4. **Frontend UI updates** - Replace ID displays with names

**Rollback:**
- DTO changes are backward compatible
- Frontend can revert to showing IDs by changing display logic
- No database changes required

## Open Questions

- Should we include `externalUserId` in the signup display? (Currently available in ShiftSignupDto)
- Do we need to include member email for any display purposes?
- Should we add name fields to shift list items (showing creator name)?
