re: REGN sections 0/1/2 have strides, and section 2 is a plane list

The three sections recorded as undecoded are fixed-stride arrays and counts[0..2]
are their record counts: 12, 96 and 48 bytes. Section 1's remainder is exactly 0
in 11/11 objects and section 2's exactly 96 in 11/11, which is what makes these
strides rather than a coincidence of division.

Section 0 is a point list: 13467 of 13467 records lie inside their object's own
header bounding box.

Section 2 is a plane list, 12 f32: four zeros, a unit normal (|n|=1 in
133573/133573), a signed distance, a point inside the bbox (133573/133573), and
a trailing 1.0 (133573/133573). The decisive check is algebraic -- n.p + d must
vanish for a real plane, and over all 133573 records the relative residual has a
median of 2.29e-08 and a maximum of 2.15e-07. That is float round-off, not a fit.

So a REGN object carries a point list and a plane list beside its uniform grid,
which fits collision or region-boundary geometry and sits next to MCOL.

Still open: section 1 (96 B, 60631 records), what queries the planes, the zeros
at [0..3], and the constant 96-byte tail.

docs/re/BACKLOG.md

@@ -349,6 +349,12 @@ search cannot find a *schedule*.
   file offsets. 🔴 **Two payload readings refuted** by generalising from the one
   object they were fitted to (a "bounding-sphere radius" float, and "leaf arrays
   of `count × 4` bytes"). The payload is float-dominated and otherwise ❔.
+  ✅ **2026-08-26: the other three sections have strides** — 12 / 96 / 48 bytes,
+  with `counts[0..2]` as their record counts (section 1's remainder is exactly 0
+  and section 2's exactly 96, in 11/11). **Section 0 is a point list**
+  (13 467/13 467 inside the bbox) and **section 2 is a plane list** — unit normal,
+  signed distance, and a point, with `n·p + d = 0` to float round-off in
+  **133 573/133 573**. Section 1 (96 B) still ❔.
   See [`structures/regn-map-grid.md`](structures/regn-map-grid.md).
 * 🔴 **`hidden/DefTables.pak` is NOT it** (checked 2026-08-24). The three
   unnamed schemas are more **model/render** tables in the same vocabulary as the