feat: add depsgraph-evaluated export example with smoke gate (#21)

examples/depsgraph-export/ proves modifiers actually ship in exports and demonstrates the depsgraph evaluated_get -> to_mesh -> to_mesh_clear lifetime contract: builds a cube + SUBSURF, measures the evaluated mesh, exports via wm.obj_export, and asserts exported vcount == evaluated (modifier-applied) count > base. Cheap CI check (no render): base 8 -> evaluated/exported 98 on both Blender 4.5.10 LTS and 5.1.1. blender-smoke.yml runs the shipped file check-only on both builds. examples/ stays out of validate-counts (12/6/2/17 unchanged); roadmap decoupled in #19 so no renumber. (Scratch candidate headless-export was NOT promoted -- it duplicates the existing tmpl_gltf smoke coverage.)

Signed-off-by: fOuttaMyPaint <TMhospitalitystrategies@gmail.com>

Author: TMHSDigital

.github/workflows/blender-smoke.yml

@@ -146,3 +146,12 @@ jobs:
           # yields geometry (eval vcount > 0 and != base); exits non-zero on failure.
           xvfb-run -a "$BLENDER" --background \
             --python examples/gn-sdf-remesh/gn_sdf_remesh.py --
+
+      - name: Shipped example - depsgraph-evaluated export
+        run: |
+          set -euo pipefail
+          # Frame-independent check only (no render): asserts wm.obj_export ships the
+          # depsgraph-evaluated (modifier-applied) geometry -- exported vcount == evaluated
+          # > base. Exits non-zero on failure.
+          xvfb-run -a "$BLENDER" --background \
+            --python examples/depsgraph-export/depsgraph_export.py --

examples/depsgraph-export/README.md

@@ -0,0 +1,26 @@
+# Depsgraph-Evaluated Export
+
+A runnable example that proves **modifiers actually ship in exports** and demonstrates the
+[`depsgraph-and-evaluated-data`](../../skills/depsgraph-and-evaluated-data/SKILL.md) lifetime
+contract. It builds a cube with a SUBSURF modifier, measures the evaluated mesh via
+`evaluated_get().to_mesh()` (paired with `to_mesh_clear()`), exports through `wm.obj_export`,
+and asserts the exported vertex count equals the **evaluated** (modifier-applied) count and is
+strictly greater than the base mesh.
+
+**What it witnesses:** the `evaluated_get` → `to_mesh` → `to_mesh_clear` contract, and that
+`wm.obj_export` writes the depsgraph-evaluated geometry (so modifiers are baked into the
+export) rather than the unmodified base mesh.
+
+## Run
+
+```bash
+# Cheap correctness check (writes an OBJ to a temp path, asserts the counts) — the CI check:
+blender --background --python depsgraph_export.py --
+
+# Write the exported OBJ to a specific path:
+blender --background --python depsgraph_export.py -- --output remeshed.obj
+```
+
+It exits non-zero on failure (modifier not applied, or exported count ≠ evaluated count). The
+`blender-smoke` workflow runs this check on Blender 4.5 LTS and 5.1: base 8 → evaluated/exported
+98 vertices with a 2-level SUBSURF.

examples/depsgraph-export/depsgraph_export.py

@@ -0,0 +1,54 @@
+"""Candidate B: depsgraph-evaluated export (SCRATCH).
+
+Witnesses the depsgraph lifetime contract AND that modifiers actually ship in exports. Builds
+a cube with a SUBSURF modifier, measures the evaluated mesh via evaluated_get().to_mesh()
+(paired with to_mesh_clear()), exports through wm.obj_export, and asserts the exported vertex
+count equals the EVALUATED (modifier-applied) count and is strictly greater than the base.
+"""
+import bpy, bmesh, sys, os, argparse
+
+def main():
+    argv = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else []
+    p = argparse.ArgumentParser()
+    p.add_argument("--output", default=None, help="optional: write the exported OBJ here (else a temp path)")
+    args = p.parse_args(argv)
+
+    bpy.ops.wm.read_factory_settings(use_empty=True)
+    me = bpy.data.meshes.new("Cube"); bm = bmesh.new(); bmesh.ops.create_cube(bm, size=2.0); bm.to_mesh(me); bm.free()
+    obj = bpy.data.objects.new("Cube", me); bpy.context.collection.objects.link(obj)
+    obj.modifiers.new("ss", 'SUBSURF').levels = 2
+    base = len(obj.data.vertices)
+
+    # depsgraph lifetime contract: evaluate, read, then release with to_mesh_clear
+    dg = bpy.context.evaluated_depsgraph_get()
+    ev = obj.evaluated_get(dg)
+    em = ev.to_mesh()
+    eval_vcount = len(em.vertices)
+    ev.to_mesh_clear()  # must be paired; releases the temporary mesh
+
+    import tempfile
+    out = args.output or os.path.join(tempfile.gettempdir(), "depsgraph_export.obj")
+    os.makedirs(os.path.dirname(os.path.abspath(out)) or ".", exist_ok=True)
+    # obj_export writes the evaluated (modifier-applied) geometry by default
+    bpy.ops.wm.obj_export(filepath=out, export_selected_objects=False)
+    if not (os.path.exists(out) and os.path.getsize(out) > 0):
+        print("ERROR: no OBJ written", file=sys.stderr); return 4
+    exported = 0
+    with open(out) as f:
+        for line in f:
+            if line.startswith("v "): exported += 1
+
+    print(f"base_vcount={base} eval_vcount={eval_vcount} exported_vcount={exported}")
+    if not (eval_vcount > base):
+        print("ERROR: evaluated mesh did not apply the modifier", file=sys.stderr); return 3
+    if exported != eval_vcount:
+        print(f"ERROR: export ({exported}) != evaluated ({eval_vcount}); modifier did not ship",
+              file=sys.stderr); return 5
+    print("depsgraph-export OK")
+    return 0
+
+if __name__ == "__main__":
+    try:
+        sys.exit(main())
+    except Exception as e:
+        import traceback; traceback.print_exc(); print(f"FATAL: {e}", file=sys.stderr); sys.exit(1)