Prevent STEP import segfault and validate required input sections

[Copilot]

Loading some STEP-based inputs can crash during adaptation (Segmentation fault) after layer import/label resolution. One failure path occurred when classification built a closed-domain vacuum from a nesting graph with no roots and dereferenced roots[0].

• Rootless graph handling in classification

  • Treat empty-root topologies as open problems in ShapesClassification::isOpenProblem().
  • This avoids routing invalid topologies into closed-domain vacuum construction.

• Defensive closed-domain construction

  • Add explicit guards in buildClosedVacuumDomain():
    • throw if no root exists
    • throw if the root is not classified as a conductor
  • Replaces unsafe indexing with deterministic runtime errors for malformed/ambiguous geometry classifications.

• Input schema validation for clearer failures

  • Add explicit validation that input JSON must include top-level array sections:
    • materials
    • layers
  • If missing, fail fast with a helpful error message.
  • When model is present instead of required top-level sections, include a specific hint in the error message.

• Regression coverage

  • Add adapter test for a rootless classification input to ensure it is classified as open and proceeds through vacuum-domain build without crashing.
  • Add adapter tests for missing layers and missing materials to validate the new input-schema error path.

auto roots = nestedGraph.roots();
if (open.size() == 1) return true;
if (roots.empty()) return true;   // new: rootless => open case
if (roots.size() > 1) return true;

[lmdiazangulo]

@copilot this seems reasonable but in this case it seems that the user put "model" rather than "layers". We should include a check that the input file includes the minimal components needed: "materials" and "layers" and show a helpful error message if it is not the case. Create a new commit in this PR to address that.

[lmdiazangulo]

@copilot Also update the documentation. It seems outdated.

[Copilot]

@copilot this seems reasonable but in this case it seems that the user put "model" rather than "layers". We should include a check that the input file includes the minimal components needed: "material...

Implemented in commit 439593e. I added explicit validation that input JSON must contain top-level array sections materials and layers, with a helpful error message (including a specific hint when model is present). I also added regression tests for missing layers and missing materials.

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[Copilot]

@copilot Also update the documentation. It seems outdated.

Updated in commit cafdb71. I refreshed docs/tulip_data_format.md so the input format now documents top-level required materials and layers (and removes the outdated <model> wrapper wording). Screenshot: no UI changes (documentation-only update).