feat: add CLI falsifiers and exit tables to ten mesh examples

[TMHSDigital]

Summary

Phase 8, retrofit batch 2. Nine mesh/GN examples plus a swatch-grid repair. Each flag feeds degenerate input into an existing assertion. Default smoke path is unchanged. README exit tables document every nonzero code the script already returned; no codes were renumbered.

--same-axis / --flat-source / #141 shape. Not skip-flags, path selectors, or second witnesses.

Parent of this branch is main @ cfc869f (v0.58.0), after squash-merge of #141.

Example	Flag	What it changes	Lands at
bmesh-gear	--no-extrude	skip extrude_face_region; closed-form counts still expect two rings	3
collision-hull-proxy	--shrink-hull	hull verts *= 0.5; containment plane test still runs	3
degenerate-bevel-weld	--both-safe	degen box uses SAFE_OFFSET; zero-area closed form still expected	4
gn-instance-grid	--one-cell	Mesh Grid 1×1; corner instance still expected at GRID_HALF	4
gn-sdf-remesh	--no-sdf	no NODES modifier; eval verts still must differ from base	3
mesh-hygiene-audit	--inject-ngon	existing inject_defect(..., "ngon")	3
triangulate-tangents	--zero-uv	every UV (0,0); polar closed form still checked	4
uv-layer-grid	--precreate-on-hazard	UV layer on the silent-no-op probe	3
wave-displace	--flat	skip foreach_set; z-span gate still runs	4
swatch-grid	--same-base	gray (0.5,0.5,0.5) on every swatch; distinct-count still 6	3

No substitutions. All nine took a genuine falsifier.

swatch-grid --no-verify check

Live-run-proven (rg -n "no-verify" tests/ .github/ scripts/ examples/swatch-grid/ plus catalog.json):

• Hits: only examples/swatch-grid/ (the flag itself, now gone; README notes the removal).
• tests/, .github/, scripts/, tests/smoke/catalog.json: no matches.
• Harness does not invoke --no-verify. Removing it does not break smoke.

--no-verify skipped the pixel check and passed vacuously. It was not renamed. It was deleted. Pixel verification still always runs when --output is passed.

A flag that only broke verify_png would exit 0 on the check-only smoke path, so --same-base targets check_distinct_swatches on the default (no-render) path. That is the existing color-identity contract, not a new witness.

catalog.json was not modified. Falsifiers are not on the default smoke path.

Live-run table

Binaries (each --version from that exe):

Tag	Path	Reports
4.5.11	.scratch/blender-4.5.11-windows-x64/blender.exe	Blender 4.5.11 LTS 4db51e9d1e1e
5.1.2	.scratch/blender-5.1.2-windows-x64/blender.exe	Blender 5.1.2 ec6e62d40fa9
5.2.1	.scratch/blender-5.2.1-windows-x64/blender.exe	Blender 5.2.1 LTS 9e2066aef7ef

Check-only (no --output). Observed exit codes were identical on all three binaries.

Example	Flag	4.5.11 def	4.5.11 flag	5.1.2 def	5.1.2 flag	5.2.1 def	5.2.1 flag
bmesh-gear	--no-extrude	0	3	0	3	0	3
collision-hull-proxy	--shrink-hull	0	3	0	3	0	3
degenerate-bevel-weld	--both-safe	0	4	0	4	0	4
gn-instance-grid	--one-cell	0	4	0	4	0	4
gn-sdf-remesh	--no-sdf	0	3	0	3	0	3
mesh-hygiene-audit	--inject-ngon	0	3	0	3	0	3
triangulate-tangents	--zero-uv	0	4	0	4	0	4
uv-layer-grid	--precreate-on-hazard	0	3	0	3	0	3
wave-displace	--flat	0	4	0	4	0	4
swatch-grid	--same-base	0	3	0	3	0	3

Live-run-proven: the 60 headless invocations (10 × 2 × 3). No falsifier exited 0. No default exited nonzero.

5.1 evidence in this PR body is local, from .scratch/blender-5.1.2-windows-x64/blender.exe. CI 5.1 is the needs-5.1 smoke job on this PR, not this table.

Inspection-only: README table wording vs sys.exit / return N in each script; rg over harness paths for --no-verify; remaining-count arithmetic (Phase 6's 41 − 6 from #141 − 10 here = 25 examples with no extra CLI flag). Did not restyle bake-normal-high-to-low or the six from #141. Did not touch pathology/sidecar five, catalog.json, VERSION, CHANGELOG.md, release.yml, blender-smoke.yml, pages.yml, gallery assets.

Test plan

• Default = 0 and falsifier = documented code on 4.5.11, 5.1.2, 5.2.1 (local, table above)
• PR smoke 4.5 + 5.2 (default path; no falsifier flags)
• PR smoke 5.1 via needs-5.1
• Validate + drift-check
• Do not merge from this session

Remaining no-falsifier pool

25 of 55 example dirs have no extra CLI flag (--output / --engine / --samples / --width excluded). Out of scope for this PR.