docs: update the REGN line - POF0 fixups in, two payload guesses out

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

docs/re/BACKLOG.md

@@ -243,10 +243,15 @@ search cannot find a *schedule*.
   none name-resolved. `REGN`'s header is now decoded: a per-map **uniform spatial
   grid** (bbox, cell size, 5³ or 10³ cells), self-checked 11/11. Its four data
   sections are unread — the 49 KB object is the cheapest way in.
-  ✅ **Section 3 is now decoded too**: one 8-byte `(count, offset)` record per
-  cell followed by 32-byte payload records, with the payload starting at
-  `align16(index end)` — **11 of 11**, and every occupied cell holds exactly one
-  record. See [`structures/regn-map-grid.md`](structures/regn-map-grid.md).
+  ✅ **Section 3 decoded**: one 8-byte `(count, offset)` record per cell followed
+  by 32-byte payload records, payload at `align16(index end)` — **11 of 11**, one
+  record per occupied cell. ✅ **And the container is a serialised object graph**:
+  every object carries a **`POF0` pointer-fixup table** at exactly
+  `header[0x04] + 16` (11 of 11), which is why the internal offsets are absolute
+  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 ❔.
+  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
   named ones — `7e66225f` (283 objects) carries `RenderFrameModel`,