Give cached bodies fresh originalIDs per call site

[revarbat]

Two identical shapes at two call sites came back sharing one originalID, so a UI keying off it treated them as one thing — selecting either picked both.

translate([60,60,0]) cylinder(h=20,r=4,$fn=32);
translate([85,60,0]) cylinder(h=20,r=4,$fn=32);

without ManifoldCache → ids [1], [2]   distinct
with    ManifoldCache → ids [3], [3]   same        ← the bug
after this change     → ids [3], [4]   distinct

A cache hit handed back the geometry and the IDs of whichever call site first produced it. Those IDs are provenance — which node made this — not content, so they cannot be cached along with the shape.

Reported against two identical cylinders. It affects any array of identical parts, which in CAD is most of them.

Per run, not per body

Each distinct run gets a fresh ID on a hit. That distinction matters: Manifold's own AsOriginal() collapses a multi-run body into a single ID —

union of two cubes: runOriginalID [1, 2]  →  as_original()  →  [5]

— which would have made a cached subtree of several parts selectable only as a whole. Each new ID inherits the old one's node and colour, so parts keep pointing at the AST nodes that actually produced them. A cached two-part module used twice yields four distinct IDs, and that is asserted.

Cost

Measured on 200 identical spheres, where every one after the first is a cache hit:

cold   170 ms
warm   128 ms

The re-stamp rebuilds each cached body from its mesh, and the cache still pays for itself comfortably.

Verification

Two new tests: distinct IDs across call sites (with the node mapping intact for both), and one-ID-per-part for a reused multi-part subtree.

The first hung on its first version — GetMeshGL() returns by value, and taking begin() and end() from two separate calls walks between unrelated buffers. Held in locals now.

803 C++ tests pass. Against a local build, BelfrySCAD's 653 tests and its GUI verifiers pass, and the two cylinders now report original_ids=[1] and [2] in the live renderer.

🤖 Generated with Claude Code