Write the nest's machine clamp rail under plateDefaults.clampRail
(width, depth, centers) so plates created or resized after a reload
still get the clamps. The key is omitted for nests without a rail, and
a missing, empty or malformed rail loads as none while each plate's
saved zones still load.
On load a plate follows the rail again only when its saved zones are
exactly the rail's for that sheet; other zones are kept as written.
The empty-plate filter now drops an empty sheet whose zones the saved
rail recreates, so the editor's trailing empty sheet is not written
for every clamped nest; empty sheets with other zones are still kept.
Add the additive per-plate clamps array (id, x, y, length, width) to the
nest DTO with writer and reader support. Files without the key load with
zero zones; an individually malformed entry is dropped while the rest of
the nest loads. A plate carrying only clamp definitions now survives the
writer's empty-plate filter; genuinely empty plates remain omitted.
Format documented in docs/nest-file-format.md.
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