re: RATC "one level deep" is not a limitation -- measured, plus a second dangling asset

INDEX read as if the parser stopped at one level. Measurement says there is
nothing deeper: 2859 top-level bundles hold 18002 children at depth 1 and ZERO at
depth 2, with no blob failing to parse.

The children that are themselves RATC -- the .rat layout records -- are leaves.
They carry no child list and reference their siblings BY NAME (the sprite they
place, and via "opt " their focused variant): 3311 such leaves, every one
embedding sibling names, and 10144 of 10148 references resolve within the same
bundle. That is the same by-name convention used one level up (a screen config
naming .prt components) and one level up again (the movie table naming
<lang>.pak+<member>).

The 4 unresolved references are a disc defect, not a parse gap: pmbase.rat in
GP_STAGE_CLEAR.pak's four language builds places pmbase.t32, and that sprite
exists nowhere -- not a pak member, not a child of those bundles. Second such
dangling asset after SUBTITLE_S12B.tbl, so a reimplementation should skip a
missing sprite rather than call it a decode failure.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/re/structures/ui-rat-layout.md

@@ -314,3 +314,27 @@ buttons are static (every keyframe identical), which is precisely why they make
 clean ruler. Validating the animation rule needs an element captured mid-slide.
 
 Evidence: [`captures/arsenal-layout-validation.png`](../captures/arsenal-layout-validation.png).
+
+## RATC nesting, measured
+
+`INDEX` carried the bundle format as 🟡 "one level deep", which reads like a
+parser limitation. It is not — **there is nothing deeper on the disc**:
+
+- **2 859** top-level RATC bundles hold **18 002** children at depth 1 and
+  **0** at depth 2, with **no** blob failing to parse.
+- The children that are themselves RATC (the `.rat` layout records) are **leaf
+  records**: they carry no child list and instead **reference their siblings by
+  name** — the sprite they place and, via `opt `, their focused variant.
+  **3 311** such leaves, every one embedding sibling names, and **10 144 of
+  10 148** references resolve to a sibling of the same bundle.
+
+That is the same by-name convention used one level up, where a screen's config
+names `.prt` components, and one level up again, where the movie table names
+`<lang>.pak+<member>`.
+
+**The 4 unresolved references are a real defect on the disc**, not a parse gap:
+`pmbase.rat` in `GP_STAGE_CLEAR.pak` (four language builds) places `pmbase.t32`,
+and that sprite exists **nowhere** — not as a pak member, not as a child of those
+bundles. It is the second such dangling asset found, after
+[`SUBTITLE_S12B.tbl`](../movie-subtitle-link.md); a reimplementation should skip
+a missing sprite rather than treat it as a decode failure.