NestPipelineResult.Unplaced lists each requirement's unplaced copies with a
typed NestUnplacedReason, counted from the returned placements: no stock fits
at the sampled rotations, reserved in a cutout of an unplaced frame, stock
exhausted, plate limit, no position found, or proposal not keepable. Desktop
Auto Nest, Console --autonest and MCP autonest_plate/autonest_job report them;
the API returns NestResponse.Unplaced, persisted from response schema 5.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>