Phase N.1 step 3: prove our inline algorithms match WorldBuilder's
helpers for representative inputs including the 0xA9B1 edge-vertex case.
Four conformance tests pass: Displace, OnRoad, GetNormalZ, ScaleObj.
Our hand-ported algorithms match WB's helpers exactly for these.
Rotation is intentionally NOT conformance-tested. Investigation against
retail's Frame::set_heading (named-retail 0x00535e40) and
Frame::set_vector_heading (0x00535db0) showed our acdream port uses a
shortcut formula `yawDeg = -(450-degrees)%360` that diverges from
retail's atan2 round-trip by ~180°. WorldBuilder's SetHeading ports
the round-trip faithfully and matches retail. Our existing port is
wrong — undetectable visually because per-tree rotation noise masks
the offset. The migration to WB.SceneryHelpers.RotateObj fixes this
bug; adding a conformance test would lock in the wrong behavior.
Bumps IsOnRoad to internal so the OnRoad conformance test can call it.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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