The guard that refuses machining through bends sewed every bend zone and
nonparallel panel into one solid. Two bends meeting at an open corner relief
share only an edge, so that sew failed with "nonmanifold edge contact" and any
cut on the base was refused. Sew and test each piece on its own instead.
Reference case 75-sm-bracket-holes now passes; its known_failure mark is removed.
Fixes#296
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>