The support grid was one shared support-grid.json, off by default, and a nest
had no machine at all, so a plasma table and a fiber laser could not have
different grids, and nothing could pick machine-specific behavior later
(lead-ins differ between laser and plasma; tabbing depends on the grid).
- Nest.Machine (id + name) persists as top-level `machine` in nest.json;
malformed values load as none.
- MachineConfig.SupportGrid holds each machine's grid; a machine without one
still falls back to the legacy support-grid.json.
- New and BOM import assign the Tools > Nest Defaults machine (first by name
when none is chosen) and give the nest that machine's grid.
- Nest > Machine reassigns a nest and swaps in the new machine's grid;
Nest > Support Grid saves machine defaults to the nest's machine.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>