Extract row subject route policy

docs/prompt-architecture-improvement-plan.md

@@ -155,6 +155,10 @@ Already isolated:
 - row subject-context routing for single, couple, configured-cast, group, and
   layout subjects lives in `subject_context.py`; it combines appearance policy,
   cast metadata, and generator subject pools behind one row-facing entry point.
+- row subject route orchestration, character slot/profile precedence,
+  configured-cast POV labels, visible cast descriptor collection, and
+  descriptor prompt cleanup live in `row_subject_route.py`;
+  `prompt_builder.py` keeps a public delegate wrapper.
 - ethnicity/filter choices, advanced filter JSON, ethnicity-list JSON, filter
   parsing, and ethnicity normalization live in `filter_config.py`; character
   routes and builder filters use `prompt_builder.py` delegate wrappers.