[scbrown]

Semantic line regions accepted thickness but always drew a one-pixel Bresenham centreline. A four-pixel line with thickness 3 now covers an 18-pixel square-brush band; omitted/thickness 1 keeps the original four pixels. This also fixes nested lines in union/subtract/intersect regions and keeps mask/validation coverage consistent with rendering.

Defines centred odd widths, a deterministic negative-side bias for even widths and an empty width-zero line. Adds odd/even/default/zero/diagonal/compound controls and an end-to-end PNG/mask/z-order/clipping test; strict clipping still reports a warning.

Validation: 2,607 passing tests across 21 native test executables with lsp,wasm, clippy all-targets with warnings denied, formatting and demo-documentation check. Native feature testing is not a browser-WASM claim; hosted CI runs the remaining surfaces.

Demo (sanitized transcript of the same local 8x8 fixture, base 686b366 versus head 4802322):

base: thickness 1: hair_pixels=4; adjacent pixel=skin
base: thickness 3: hair_pixels=4; adjacent pixel=skin
head: thickness 1: hair_pixels=4; adjacent pixel=skin
head: thickness 3: hair_pixels=18; adjacent pixel=hair
head: nested thickness 3: hair_pixels=18; adjacent pixel=hair

Reproduce with cargo test --test line_thickness --features lsp,wasm, or render a region {line:[[2,4],[5,4]],thickness:3} on an 8x8 canvas, then pxl mask fixture.pxl --sprite thick --count --json. The transcript reports actual local candidate behavior; it is not an installed release claim. A replayable terminal capture is retained privately; no public recording host is configured.

Bead: aegis-8t76.1

Overlap preflight: 4f53cda18c2baa0c0354bb5f9a3ecbe5ed12ab4d8e11ba873c2f11161202b945

Current integration refresh c6939d4e9d44145b022195143081284b4da08f8e includes base c665831c after the publishing repair landed. The entire three-path line-thickness proposal replays forward and inverse exactly, with no behavior changes in the refresh. The line-thickness PNG/mask control passes at this candidate; fresh hosted CI remains required. Earlier test-launch attempts stopped before testing because the sandbox lacked toolchain configuration; the successful run uses explicit compiler paths, with HOME guard verification retained privately. No release, tag, publication or product installation is requested.