docs: SMLib vs truck triage of the sweeps, threads and shell cases

169 rig and ladder cases on both kernels, graded against each case's own answer: where SMLib
fails, grouped by what goes wrong (wrong geometry, a crash, the thread groove's boolean failing
SMLib's check, shell refusals, sweeps with no SMLib path yet).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/kernel-smlib-sweeps-shell.md

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+# SMLib vs truck: sweeps, threads, shell and offset
+
+A triage of the regression rig's sweeps, threads and shell cases, and of the ladder's tiers 03
+(analytic profiles), 04 (spline profiles), 06 (threads) and 09 (shells and offsets): 169 cases,
+each run on both kernels (`solidcraft-cli kernel-cases`, `SOLIDCRAFT_KERNEL` unset and `smlib`)
+on `kernel-smlib` at 4b8953726. Each kernel is graded against the case's own answer
+([kernel-cases.md](kernel-cases.md)), not against the other kernel. This page lists only the
+cases where SMLib does not pass, grouped by what goes wrong, worst first; it is kept by hand as
+fixes land.
+
+| | Cases | truck passes | SMLib passes |
+|---|---|---|---|
+| sweeps | 83 | 55 | 51 |
+| threads | 28 | 10 | 11 |
+| shell | 18 | 5 | 11 |
+| ladder 03, 04, 06, 09 | 40 | 28 | 26 |
+| **all** | **169** | **98** | **99** |
+
+SMLib passes 18 cases truck fails (shells of tapered and rounded bodies, offset faces next to
+freeform faces, bent and hollow lofts, the 36 twisted blades). Truck passes 17 that SMLib does
+not: 11 of them are sweeps SMLib has no path for yet (group G), 6 are below.
+
+A thread off its hole's or shaft's size is refused on this branch (the owner's rule): those
+cases pass on both kernels by refusing, and are not listed.
+
+## A. Wrong geometry (worst)
+
+| Case | truck | SMLib | SMLib's result |
+|---|---|---|---|
+| sweeps/2667-revolve-half-disc-three-quarters | pass | fail | a half disc on the axis turned 270°: SMLib makes a quarter ball turned inside out (V = -226, want 679) |
+| sweeps/3528-revolved-dome-cut-by-a-ball-on-its-seam | pass | fail | the ball's cut is lost where it crosses the revolve's seam: V 48118, want 46425 |
+| sweeps/2847-loft-rectangles-turning-through-half-a-turn | fail | fail | inside out (V = -127, want 2262); truck's is wrong too (V = 126) |
+| sweeps/450-revolve-spherical-shell-sketched-off-the-origin | crash | fail | two shells where one is wanted, which the B-rep record can't close (truck's process dies) |
+
+## B. Crash
+
+| Case | truck | SMLib | SMLib's result |
+|---|---|---|---|
+| ladder/09-shells-and-offsets/011-part-shell | fail | crash | step 21 (solid.fillet) on the SMLib body: curve blend internal error "Two same vertices cannot construct an edge"; the fillet is the blends work's, not this page's |
+
+## C. Threads: the groove's boolean fails SMLib's check
+
+The groove (SMLib's screw sweep) cuts the body, and the result fails SMLib's own check: vertex
+gaps of 1–6e-5 mm against vertex tolerances of 4–20e-6 mm (Test #0/#2 Bad Gap), an edge whose
+geometry fails validation (Test #61), or a trim curve that does not lie on its edge when the
+result is read back (SMLib export: pcurve). Truck's faceted groove fails SMLib's check on the
+same cases with 6 to 752 failed tests.
+
+| Case | truck | SMLib | SMLib's result |
+|---|---|---|---|
+| ladder/06-threads/001-external-m10-full | fail | fail | Bad Gap (1.89e-5 > 8.6e-6) |
+| ladder/06-threads/002-external-m10x1-fine | hang | fail | Test #61 bad edge |
+| ladder/06-threads/003-external-m10-partial-length | pass | fail | Bad Gap (1.91e-5 > 8.9e-6) |
+| ladder/06-threads/004-external-m10-to-shoulder | fail | fail | Bad Gap ×10 |
+| ladder/06-threads/005-internal-m10-through | fail | fail | Bad Gap (3.6e-5 > 1.8e-5) |
+| ladder/06-threads/006-external-m10-into-chamfer | fail | fail | Bad Gap |
+| ladder/06-threads/007-external-m10-at-filleted-shoulder | fail | fail | Bad Gap |
+| ladder/06-threads/010-part-threaded-boss | fail | fail | Bad Gap (2.26e-5 > 2.0e-5) |
+| threads/1250-external-m10x1.5-shaft-full-length | fail | fail | Bad Gap ×9 |
+| threads/1395-long-external-m6-thread-24-turns | fail | fail | Test #61 bad edge |
+| threads/1995-m8x1-thread-in-7mm-hole | fail | fail | Bad Gap (1.5e-5 > 7.5e-6) |
+| threads/2038-cut-threaded-stud-from-bored-block | fail | fail | Test #61 bad edge |
+| threads/2038-internal-then-external-thread-on-one-body | fail | fail | pcurve off its edge |
+| threads/2038-join-two-threaded-bodies | hang | fail | pcurve off its edge |
+| threads/2193-modelled-m33x3.5-thread | fail | fail | Bad Gap |
+| threads/2209-fine-m44x1-thread-on-shaft | fail | fail | Bad Gap ×7 |
+| threads/2209-m44x1.5-thread-on-flange-hub | fail | fail | Bad Gap (6.2e-5 > 2.05e-5) |
+| threads/2406-modelled-m8-thread-in-6.8mm-pilot-hole | fail | fail | Bad Gap |
+| threads/2526-three-modelled-threads-in-one-body | fail | fail | pcurve off its edge |
+| threads/2822-modelled-thread-in-filleted-cube | fail | fail | pcurve off its edge |
+| threads/3311-two-tapped-holes-both-modelled-threaded | fail | fail | pcurve off its edge |
+| threads/3914-sketch-on-top-face-of-threaded-rounded-block | fail | fail | pcurve off its edge (0.86 mm) |
+| threads/3952-modelled-thread-in-blind-hole-of-revolved-ring | fail | fail | pcurve off its edge |
+| threads/4149-internal-thread-below-counterbore-filleted-rim | fail | fail | Bad Gap |
+| threads/602-fillet-hex-head-beside-modelled-thread | fail | fail | Bad Gap |
+
+## D. Coils and other sweeps in booleans
+
+| Case | truck | SMLib | SMLib's result |
+|---|---|---|---|
+| sweeps/793-coil-cut-by-a-box-above-a-plane | hang | fail | pcurve off its edge |
+| sweeps/793-coil-split-by-a-plane-across-its-axis | fail | fail | pcurve off its edge |
+| sweeps/2552-thread-groove-cut-by-a-square-coil-in-a-bore | hang | fail | the boolean's result is not a closed solid |
+| sweeps/96-loft-cut-box-sections-pad-first | fail | fail | the boolean's result is not a closed solid |
+| sweeps/96-loft-cut-box-sections-top-first | fail | fail | the boolean's result is not a closed solid |
+| sweeps/844-join-two-overlapping-swept-arc-walls | fail | fail | boolean status 1006 |
+| sweeps/3006-second-sweep-from-a-plane-along-a-closed-path | fail | fail | read back: a face no shell uses |
+
+## E. Shell and offset refused
+
+| Case | truck | SMLib | SMLib's result |
+|---|---|---|---|
+| ladder/09-shells-and-offsets/006-shell-rounds-r1-thinner-than-t2 | pass | fail | shell status 1001 (rounds of r1 inside a 2 mm wall) |
+| shell/1494-shell-box-with-cylinder-on-edge-line | fail | fail | shell status 1001 |
+| shell/1525-shell-box-with-rounds-chamfer-and-fillet | fail | fail | shell status 1001 |
+| shell/2939-offset-face-sphere | pass | fail | check: edge/surface gap 5.015e-6 > 5e-6 |
+| shell/3468-offset-face-boss-wall-next-to-fillet | fail | fail | check: an edge tolerance of 2.0 mm |
+| shell/2531-shell-point-pick-after-parameter-edit | fail | fail | V 17952, want 22112 (truck 17376): the shell's face pick after the edit, on both kernels |
+| sweeps/2820-pipe-hollow-with-a-wall-along-a-bend | pass | fail | sweep status 1001 |
+
+## F. Same answer on both kernels (engine or case)
+
+| Case | truck | SMLib | Both kernels |
+|---|---|---|---|
+| sweeps/3345-sweep-profile-mid-line-round-a-rounded-rectangle | fail | fail | the same bbox (±46 × ±36, want ±32 × ±22): the profile's placement, not the kernel |
+| sweeps/2516-revolve-about-a-named-construction-axis | fail | fail | unknown sketch line `Axis1` |
+| sweeps/3191-revolve-cut-leaves-a-cone | fail | fail | the profile crosses the revolve axis |
+| sweeps/4056-surface-loft-rails-…-stern-to-bow | fail | fail | a guide rail misses section 2 |
+| sweeps/2570-loft-circle-to-a-non-star-shaped-comb | fail | fail | SMLib: an arc turns more than once; truck: a loop runs clockwise |
+| shell/4009-closed-shell-internal-void | fail | fail | `solid.shell` needs 1…1000 faces (a closed shell has none) |
+| ladder/06-threads/008-multi-start-thread | unsupported | unsupported | no start count yet |
+| ladder/06-threads/009-thread-runout-length | unsupported | unsupported | no runout length yet |
+
+## G. No SMLib path yet ("not supported yet", never truck's in its place)
+
+| What | Cases |
+|---|---|
+| sweep with a twist or an end scale | sweeps/1269-sweep-twisted-square-ninety-degrees, 2005-closed-sweep-twisted-new-body, 2005-closed-sweep-twisted-cut-inside-a-torus, 2891-twisted-sweep-cut-through-a-tube, 771-sweep-end-scale-cone-frustum |
+| sweep along a path with corners | ladder/04/003-pipe-along-bezier, ladder/04/004-sweep-square-along-bezier, sweeps/96-sweep-rectangle-round-a-mitred-corner, 561-extrude-the-end-face-of-a-sweep, 3505-extrude-the-flat-wall-of-a-sweep-with-a-corner |
+| loft through sections with holes | sweeps/1184-loft-ring-sections-keep-the-hole, 2435-loft-rectangular-ring-sections, 3111-loft-rectangular-ring-to-circular-ring |
+| guide rails | sweeps/201-loft-one-guide-rail-cone-frustum, 771-sweep-one-guide-rail-cone-frustum, 771-sweep-two-guide-rails-cone-frustum |
+| sweep along a path of points | sweeps/2862-three-pipes-meeting-at-one-point |
+| draft extrusion with a straight foot | shell/391-deboss-text-on-flange-of-filleted-shelled-body |