2d. Connectivity belongs to the assembly, not to the artwork

kerfmaster pin list · Big capabilities

intentclosed d15What we want to build. Never claimed the present, so it cannot be stale — and must never be read as a description of the code.

Content last changed 2026-08-06 — computed from the item itself, not typed.

Contract — Bridges stage

This contract describes a stage we intend to build — it is NOT a description of the code.

takes topologystack-up

makes bridged-part

fails if Connectivity measured on the composite instead of per plate; a weld chord that exists only because two plates happen to overlap.

Contract last changed 2026-08-06 — computed, not typed. Dated separately from the text above, so neither date can speak for the other.

1 open question blocks this pin

Q14 Does a strip roughly 1.6 by 0.20 inches, cut on both sides in 1/8 steel, stay flat or bow?
Jordan — The width of an added weld chord depends on the answer.

⚠ Known defects

This item's subject has a known defect in the code. Source: cadmaster/defects.json → cadmaster/KNOWN_DEFECTS.md, not this page — the text below is generated from the register so the two can never disagree.

D15 — The cloud loses its whole top-left lobe: a subpath is subtracted as if it were a hole, and the two shapes are disjoint so the boolean is a no-op (CLOSED)
mvt_prep.py:~18 builds the cloud as Polygon(cloud[0]).difference(Polygon(cloud[1])). Path 2 of the MVT artwork has TWO subpaths: sub0 is the cloud body (9056.6 pt2) and sub1 is the big top-left lobe (2506.4 pt2). They are DISJOINT, not nested, so they are a UNION -- two pieces of one filled shape -- and the difference of two disjoint polygons is the first one, unchanged. The lobe is dropped and the area is identical before and after: 9056.6 in, 9056.6 out. Every downstream figure (area, weight, centre of mass, tipping) was computed from the truncated cloud.
Cost today: Nothing further is computed from the truncated cloud. What is still outstanding is the customer-facing reissue: revision Q0QB remains WITHDRAWN and no replacement sheet has been published. Option C's cloud goes from the published 8.84 lb to 11.83 lb, and the assembly from 12.21 lb to 15.32 lb.
Verified: 2026-08-06, FIXED and verified at the source. mvt_prep no longer reads an SVG export: the artwork comes out of the customer's modified .ai through mvt_geom, and the cloud is one closed Polygon of 11710.1 pt2 = 333.38 in2 = 11.83 lb. Control through an independent path -- MVT_MODIFIED_MEASURED.md was written by hand from the same file before mvt_geom existed, and all ten of its figures reproduce, worst disagreement 0.15% (total weight, 15.323 vs a hand-rounded 15.30). The general rule is now enforced rather than assumed: a cloud that arrives in more than one piece RAISES, because disjoint pieces are a union, and every boolean goes through mvt_geom.changed(), which states the area it should move and raises when it does not. NOT YET DONE: the published sheets have not been reissued, so revision Q0QB stays withdrawn until the A/B/C rebuild runs.

The rule. Connectivity is a property of the assembly, not of the artwork. A shape is very often held to its neighbour only because the composition happens to overlap them — which is a by-product of the drawing, not a decision anyone made. Split that composition into plates and the hold is deleted, silently, because nothing in the geometry ever said it was load-bearing.

Three checks — none of them built

Recompute connectivity per plate, after every split. Never once on the assembled art. The assembled art is the one configuration that is guaranteed not to be cut.
Measure and report the weld chord of every contact between filled shapes — the actual width of metal where they meet, in inches, on the plate that will be cut.
Flag tangency as distinct from connection. Two shapes that meet at a point are not joined; two shapes that overlap by a hair are joined by a hair. Both render identically on screen.

The example that produced the rule. On the MVT icon the cloud's top lobe met the ring with a weld chord of 0.002 inch. That reads as solid on any screen at any zoom, and it is nothing in steel — it would not survive being lifted off the table. Aristide's own fix took the opposite approach and is the reference: he added metal until the narrowest neck anywhere in the cloud was 1.029 inch.

Related: Island (an island is defined by connectivity, so it is defined per plate too) and item 2b (a bridge is the deliberate version of what this pin measures accidentally).

src — MVT icon, 2026-08-06. Written up in cadmaster/LESSONS_MVT_ASSEMBLY.md (a4b3034). Typed intent: none of it is built.