Synchronize pair cast metadata

docs/prompt-architecture-improvement-plan.md

@@ -273,7 +273,7 @@ Already isolated:
   caption-part joining, embedded soft/hard row output synchronization, and row
   sanitation before metadata leaves generation. It also copies side-specific
   pair metadata, such as soft partner styling and hardcore clothing/detail
-  state, onto the embedded soft/hard rows.
+  state, plus shared cast descriptors, onto the embedded soft/hard rows.
 - final custom-row assembly now lives in `row_assembly.py` behind
   `CustomRowAssemblyRequest`, covering render context population,
   prompt/caption rendering delegation, row-base indexing, row metadata copying,
@@ -326,8 +326,9 @@ Already isolated:
   Embedded soft/hard rows are synchronized to the final pair prompt, caption,
   and negative outputs during normalization so serialized pair metadata does
   not carry stale standalone row text. Side-specific structured fields are
-  synchronized there too, including soft partner styling and hardcore clothing
-  continuity metadata.
+  synchronized there too, including soft partner styling, hardcore clothing
+  continuity metadata, and shared cast descriptors for same-cast caption and
+  formatter routes.
 
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