[lightningpixel]

Closes #296

Summary

Adds two read-only operations to the mesh_ops registry so the agent can diagnose a mesh before acting on it — "Is this mesh printable?" now returns an accurate diagnostic without modifying anything.

• inspect_mesh — watertight, manifold, consistent winding, holes (count, open edges, largest hole), non-manifold edges, degenerate faces, self-intersecting faces, disconnected parts, bounds/dimensions, surface area, volume (only when closed), UVs/normals, and a printable verdict with a list of issues.
• suggest_fixes — derives registry op calls from the report (repair with flags matching the detected problems and a max_hole_size sized to the largest hole, decimate above 500k faces). Problems no op can fix yet (winding, self-intersections, stray parts) are returned as notes instead of invented fixes.

Changes

• api/services/mesh_ops/inspection.py — new module; both ops registered in builtin.py under the analysis category (non-destructive).
• MeshOpResult.file_path is now optional: analysis ops produce no file. /optimize/op/{id} returns the bare report for them; the workflow processor rejects them explicitly.
• Agent: new inspect_mesh and suggest_fixes tools, and a prompt rule to inspect rather than guess.
• MCP server: modly_inspect_mesh and modly_suggest_fixes.

Design notes

• Topology is computed on a position-merged copy of the geometry (scene transforms applied), so UV seams don't read as holes — a naive trimesh load reports textured closed meshes as non-watertight.
• Self-intersections use pymeshlab (already a repair dependency), in memory. They can be skipped with check_self_intersections: false; printable is then null instead of a claim.
• Normals are read from the file (glTF NORMAL attribute, OBJ vn, PLY nx), since trimesh always computes them on demand.

Testing

• npm run test:py — 240 tests pass (4 skipped). 15 new inspection tests on real exported meshes (closed/open box, UV seams, multi-node scene, overlapping parts, normals per format, input never modified), plus router and agent tests.
• Diagnostic → suggested repair → re-inspection gives a printable mesh.
• Cross-checked against MeshLab's topological measures on Khronos sample models (Duck, Avocado, DamagedHelmet, BoxTextured): boundary edges, components, holes and non-manifold edges match exactly.
• Timing: ~2 s for 327k faces, ~8 s for 1.3M faces with self-intersections.

Follow-ups

• The agent can see that repair is needed but has no tool to run it (only decimate/smooth) — a generic "run registry op" tool belongs to a later Epic A ticket.
• Not yet run on real TripoSR / Hunyuan outputs.