[dbritto-dev]

What this changes

Adds offsetPath(points, by, limit = 4) to the kit: a floor polyline moved sideways by by, point for point.

• A positive by moves a path that runs along +x toward +y.
• Interior corners are mitred so both adjacent legs stay exactly by away; a mitre never reaches past limit × by from its corner (like SVG's stroke-miterlimit).
• Repeated points take the direction of their nearest real segment, so they move with their neighbours; a single point, or a path of one repeated point, stays put.

It is in kit/iso-kit.ts and kit/iso-kit.mjs (the transpiled output, unchanged elsewhere), listed in references/kit.md under "Solids" next to insetPlan, and covered by scripts/offset-path.test.mjs: straight paths both ways, square corners inside and outside, the exact by distance from both segments along a curve, the mitre limit on a hairpin, repeated points, and the TypeScript twin.

Why

Two-edged things follow one centreline: both rails of a track, the edges of a belt, a lane, a road, a pair of parallel cables. The kit can fillet, resample, cut and walk a path, but not offset one, so a figure had to compute normals and corner joins itself. A railway-junction figure needed it for its bed, both rails and its sleepers.

Checks

• Every example rebuilds, and git status --short shows only the changes I meant. The pages that inline the kit (dial indicator, desk computer, arcade cabinet, ripple tank, push button, both themes) gain the function and nothing else.
• No comments in code.
• Kit changes are opt-in: one new export, no existing function changes.
• I built and looked at both themes (demo below).
• Audit: node examples/raptor-engine/build.mjs --light --audit ends audit passed on this branch (80 tubes, 267 solids, 478 items, 1,119 depth states). This PR changes no pipe, cable or round part.
• node scripts/lines.mjs prints line ends: 0 on all ten pages this PR changes: dial indicator, desk computer, arcade cabinet, ripple tank and push button, light and dark.
• Shaders: the ripple tank is the only shader page that changes (it inlines the kit; no shader source changed). Its reduced-motion stills are pixel-identical to main (0 differing pixels), light and dark, with WebGL and with --no-webgl.
• 3D: a full node examples/turning-dial/build.mjs --light --audit on this branch reports the same 4 problems as main, where the full report is every line 0 except crowding: 4 (cable.green end × hand.f3.p1 at 165°, cable.blue end × hand.f3.p1 at 200°, cable.red end × hand.f1.p1 at 210°, cable.green end × hand.piston.rod at 285°), so they come from the turning-dial example, not this PR. scripts/turn-check.mjs examples/turning-dial/build.mjs --fidelity passes, and the turning-dial pages rebuild byte-identical to main.
• Every number in the docs is true.
• A line under Unreleased in CHANGELOG.md.

node --test scripts/*.test.mjs: 296 of 296 pass.

This and the sideOutline PR (#136) each add a CHANGELOG.md line in the same spot, so whichever merges second needs a one-line rebase.

Screenshots

A demo plate (not committed): the bed edges (±8), both rails (±4) and the sleepers all come from one S-curve centreline through offsetPath.

Light	Dark

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🤖 Generated with Claude Code

https://claude.ai/code/session_01S5z2gCvevbrGU3fXgpGDmP

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