entity_wires() cloned the entire wire set — every point, fill, and snap
buffer of every entity — on each call, although the set is already
memoized behind an Arc and none of the 18 call sites mutates it. On
large mesh imports (#358: 42M faces, ~210 MB of wire content per 1M
triangles) that is a multi-GB allocation + memcpy on every pick, snap,
selection, or plot pass.
Return the Arc instead. Call sites iterate as before; the two
window-plot paths that build a culled owned subset now clone only the
wires inside the plot window, and the print pipeline moves the Arc into
its async task.
Measured (tests/mem_probe_meshent.rs, 1M-triangle MESH, release):
resident after entity_wires() drops 758 -> 547 MB (866 -> 646 B/face).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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