fix(examples): make the examples follow the rules they teach, and lint it

[TMHSDigital]

Closes #400.

Problem

Agents copy these scripts (bmesh-gear is the documented anatomy), but nothing checked them against the repo's own rules, and they broke them.

Change

• Scripted AST rewrite: 127 loops in 100 files.
  • for p in X.polygons: p.use_smooth = E becomes X.polygons.foreach_set("use_smooth", …). That is a constant fill when E doesn't use p, and a comprehension otherwise.
  • for v in X.vertices: v.co.z += D becomes foreach_get → shift co[2::3] → foreach_set.
  • Inline comments are carried over. No collision with existing _co names in the same function (checked).
• 7 by hand:
  • constant material_index fills: boolean-exact-volume, depsgraph-export, gn-sdf-remesh, soccer seams;
  • uniform co scale and offset: prop-origin-transform ×2, collision-hull --shrink-hull;
  • moka-pot --lean-pot.
• 8 marked # foreach-exempt: <why>. These have genuinely per-element logic: car-mirror ring bands, collision-hull bonnet height, the lightmap post arc fit, mesh-hygiene n-gon marking, the soccer pentagon test, triangulate-tangents build-order bands, and the bowling-ball surface test.
• 7 active_object reads (compositor-glare, gn-sdf-remesh ×3, grease-pencil-rosette ×2, turntable) get if X is None: raise RuntimeError(...).
• New tests/check_example_rules.py in Validate. It flags:
  • an unmarked per-element write in a loop over .polygons/.vertices. Those names exist only on Mesh, since BMesh uses faces/verts, so bmesh code never triggers it;
  • an active_object assignment not directly followed by if X is None.
• docs/new-example-prompt.md documents the lint and the marker.
• Out of scope: the bmesh-lifetime half of showcase: hay-bale leaks a bmesh via 'finally: pass'; always-free-bmesh rule disagrees with builder/ownership-transfer code #401 (builder classes that own a BMesh). It stays tracked there.

Evidence

Equivalence, live run. Binary reports 5.2.1 LTS. Each pair runs main's script and this branch's:

Script / args	exit (old/new)	stdout identical
bmesh-gear	0/0	yes
anvil · anvil --lift-z	0/0 · 16/16	yes · yes
moka-pot --lean-pot · --lift-z	19/19 · 16/16	yes · yes
prop-origin-transform	0/0	yes
collision-hull-proxy · --shrink-hull	0/0 · 3/3	yes · yes
soccer-ball-goldberg · --invert-bind	0/0 · 13/13	yes · yes

"Identical" excludes timing and temp-path lines. CI smoke runs every happy path and catalog falsifier on 5.2 and 4.5.

Checker: passes on 140 scripts. On main it reports 15 violations after the scripted pass, which are the hand-fixed and marked sites above.

check_helper_drift, check_exit_code_readme, check_render_gates, check_engine_id and check_witnesses pass. The gallery is unchanged: it links sources rather than inlining them.

🤖 Generated with Claude Code

[TMHSDigital]

CI evidence before merge: all checks pass ( 13 pass ). Blender Smoke on PR head: Blender 5.2.2 LTS / Blender 4.5.14 LTS. Summaries (happy path; falsifiers) per leg: 141 passed, 3 skipped, 0 failed;136 passed, 7 skipped, 0 failed;143 passed, 1 skipped, 0 failed;143 passed, 0 skipped, 0 failed;