Remove redundant shelf lookup (double DB hit)

[leodvincci]

Remove redundant shelf lookup (double DB hit)

Type: Performance / Refactor
Priority: P2

Summary

findShelfById() and isFull() each load shelf separately.

Impact

Extra round-trip; worse if shelf becomes remote.

Evidence

bookCommandUseCases.java lines 28 and 33.

if (!shelfAccessPort.findShelfById(shelfAssignmentRequest.shelfId()).isPresent()) {
  throw new IllegalStateException(
      "Shelf not found with id: " + shelfAssignmentRequest.shelfId());
}

if (shelfAccessPort.isFull(shelfAssignmentRequest.shelfId())) {
  throw new IllegalStateException(
      "Shelf with id " + shelfAssignmentRequest.shelfId() + " is full");
}

Proposed Fix

Consolidate into single validation call or reuse loaded shelf data.

Acceptance Criteria

• Only one shelf query per placement.

Expected

Shelf validation performs one lookup per placement (or single remote call).

Actual

Shelf is loaded twice: once for findShelfById(), again for isFull().