re: the RATC +0x0c interval is authored, not a keyframe extent

Tested the alternative I recorded last iteration. Parsing every bundle's
keyframe times (2985/2985 parse), the derived-summary reading -- (high,low) ==
(min,max) keyframe time -- holds in 6 of 2985 (0.2%).

The apparent 34.2% match on 'high == min' is a coincidence of zeros: the minimum
keyframe time is 0 in 96% of bundles and high is 0 in 34.9%, so the 1022
'matches' are exactly the both-zero cases. Worth noting that last iteration I
declined to treat the high==0 share as support -- it turned out to be the
confound rather than the signal.

The interval is also narrow: (low-high)/(max-min) has a median of 0.019, about
2% of the keyframe span. It lies inside the keyframe range in 88.6%, entirely
after in 174 and entirely before in 68.

A short authored window is not the shape of a playback range or a whole-animation
loop region, so those readings weaken too. What it is stays open.

docs/re/BACKLOG.md

@@ -305,8 +305,10 @@ See [`structures/ui-composable-bundles.md`](structures/ui-composable-bundles.md)
   the only supporting evidence is that the twelve 30.0 bundles cap at `+0x08`=30
   while the 2 843 60.0 ones reach 1 440. ✅ `+0x0c` is **two u16s forming an ordered
   interval** — `high < low` in **2 985/2 985**, both bounded by the animation
-  length; 🟡 which interval, and ❔ whether it is authored or just the keyframe
-  min/max, is untested. `+0x10` still ❔.
+  length; ✅ it is **authored, not the keyframe min/max** — that
+  reading holds in 6 of 2 985 (0.2 %), and the apparent 34 % match on `high` is a
+  coincidence of zeros. The window is narrow, a median 2 % of the keyframe span.
+  🟡 what the window means stays open. `+0x10` still ❔.
   See [`structures/ui-rat-layout.md`](structures/ui-rat-layout.md).
 * 🟡 **What `opt ` links — a record→record reference** (2026-08-24, measured
   disc-wide and asserted). All **1 467** links reachable from a declaration table