E01 · F04 · SP-007 — Research for F04

Find, read and record the sources of every story of F04 before its implementation (ADR-0020).

Acceptance criteria

Given each story of F04, when the spike ends, then every formula and behavior it needs has a verified REF-* or a DERIV-*.
Given the sources found, when the spike ends, then the stories cite them, and a research note records what was found and what remains open.

Turning a point about a center, clockwise on screen in the SVG frame (y down): the formula and a source (SVG transforms, rotate(a, cx, cy)); exact values at 0, 90, 180, 270 (cos and sin of 90° are not exact in floating point).
An angle kept from 0 to 359: the remainder of a negative number in ECMAScript (% keeps the sign), stated in TSDoc (ADR-0025).
The straight box of a contour of segments and circular arcs: where an arc reaches its extreme x and y (the axis directions it sweeps); how browsers define getBBox.
The model: what the position stores (the straight box's top-left, or a translation from which it is derived), how it stays without loss when the shape turns back and forth; an ADR (every shape gets an angle and a position, ADR-0003 and ADR-0034).
Editing a turned shape: which point stays fixed when the width changes (Figma's behavior as a functional reference), a point typed in the SVG's coordinates turned back into the shape's box.

One task = one commit, referenced as SP-007.Tn.