**Problem:** Broad exception handlers created fragility where adding a new
DomainError subclass without explicit registration would silently fall through
to the generic exception handler, losing the specific error_code and metadata.
**Solution:**
1. Import DomainError in main.py for explicit handler registration
2. Fix type hints in exception handlers from 'Exception' to specific types
- NotFoundError handler now typed as 'NotFoundError'
- BadRequestError handler now typed as 'BadRequestError'
- ConflictError handler now typed as 'ConflictError'
- DomainError handler now typed as 'DomainError'
- ServiceUnavailableError handler now typed as 'ServiceUnavailableError'
3. Add DomainError as an explicit catch-all handler in the registration chain
- Positioned after specific handlers, before HTTPException
- Any unregistered DomainError subclass now gets correct error_code + metadata
4. Document the exception handler hierarchy with detailed comments
5. Update Backend-Development.md with handler hierarchy documentation
6. Update Architekture.md section 2.2 with exception handler details
7. Fix test expectations in test_main.py to verify ErrorResponse format
**Impact:** Any new DomainError subclass now automatically gets correct HTTP 500
status, error_code, and metadata - even if developer forgets explicit handler.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Lukas
2db635ae19