docs(audiobook): record the rejected scene-cast experiment

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TODO.md

@@ -345,8 +345,9 @@ Still open (each needs a real decision or new evidence, not more prompt tuning):
   until the book itself ties it to a name.
 - [ ] Look-alike main characters in one scene (Marcian/Zerwas/Lancorian) remain the biggest real error
   class (~1/5 of spoken words). Tried and rejected: reasoning mode (25× slower, no gain), larger/smaller
-  windows, tag-based overrides, reasoning adjudication of disputes (made disputed lines worse). Untried:
-  an explicit scene-cast constraint (characters present in the scene) built from the text.
+  windows, tag-based overrides, reasoning adjudication of disputes (made disputed lines worse), an explicit
+  scene-cast hint (names mentioned in the passage: +0.3 points, noise). What remains is mostly model
+  capacity plus reference noise; the useful lever left is human review guided by the agreed/disputed flags.
 
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architecture/audiobook-attribution.md

@@ -132,7 +132,8 @@ lines) but compared against a biased baseline; on the real pipeline it made the
 so the adjudication step (and the `candidates` request field) was removed. The only reliable signal is
 agreement itself: agreed lines are right 82 % of the time, contested first answers 67 %.
 Sampling matters: windows of ~1 200 characters were clearly worse (−4 points) and ~5 000 about equal to
-the default, so the default stays.
+the default, so the default stays. A scene-cast hint (which known characters are named in the passage or
+just before it) gave +0.3 points — noise — and was not adopted.
 
 Request additions: `attribute_only` `[ids]` — the other spans are context; unrequested lines are never
 reported missing.