The positioning engine is pure collision geometry over `$adom` — a runtime
artifact, not soma-specific. Moves it out of `soma/layers/floating/engine/` into
a new `arts/floating` art (`$floating`), exactly parallel to `$motion`: both soma
(the JS positioning path) and eidos (the CSS-anchor path, future) build on it,
so the shared pure core belongs in arts, not buried in one consumer.
Moved to `$floating` (git renames, history preserved): geometry, rects, clipping,
overflow, supports, compute, auto-update, flag, types, the 7 middleware, and the
two parity test suites. `placement.ts` and the contract types `Measurable` /
`Middleware` / `MiddlewareData` move too — `$floating` is now self-contained
(depends only on `$adom`, never back on soma). New `arts/floating/index.ts` barrel
is the public surface. Alias `$floating` added to vite.config.ts + svelte.config.js.
Stays in `soma/layers/floating/` (reactive composition): use-floating.svelte.ts
(runes), floating.svelte.ts (providers/context), shell.ts, safe-polygon.ts,
utils.ts, the reactive types, index.ts. These now import `$floating`; soma's
types.ts/index.ts + soma/types/index.ts re-export the placement/contract types.
Two latent type gaps the typed `$floating` surface exposed (the soma loose-factory
shim had hidden them) are fixed: `DetectOverflowOptions` now declares `boundary`
(the middleware genuinely accept it; compute's read phase extracts it), and a
`size` test's `apply` returns void.
`@floating-ui` is UNTOUCHED — P4 deliberately NOT executed: the dep stays installed,
the fui imports + the `USE_OWN_ENGINE` flag (still OFF) remain in the wrappers, the
runtime still positions via floating-ui. Verified: 350 synthetic + 137 real-DOM
parity cases green from the new location, soma overlay providers green, check clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
