Trim and validate scene caveats

docs/internal/modules.md

@@ -88,7 +88,8 @@ last, exact source-unit IDs, sequential contiguous scenes, and no overlap. It
 assigns chunk IDs such as `scene-000001` and stores scene metadata including
 title, primary mode, participants, summary, boundary note, confidence, boundary
 unit IDs, and unit count. Boundary caveats become warnings with reason code
-`scene_boundary_caveat`.
+`scene_boundary_caveat`. Whitespace-only caveats are treated as malformed
+structured output rather than silently dropped.
 
 Malformed model output fails explicitly rather than falling back to another
 chunker. The chunker exposes prompt and response-schema provenance through

docs/troubleshooting.md

@@ -183,6 +183,7 @@ Symptoms include:
 
 - `dnd scenes chunker`
 - `malformed structured output`
+- `boundary_caveats`
 - `start_unit_id`
 - `end_unit_id`
 - `gap`
@@ -199,6 +200,8 @@ Fix:
 - Inspect retained diagnostics for the run error and resolved pipeline.
 - If the error names malformed structured output, retry with a model that
   follows structured response schemas reliably.
+- If the error names `boundary_caveats`, check for blank or whitespace-only
+  caveat text in the scene response.
 - Scene boundaries must use exact source-unit IDs, cover the full source
   document, be contiguous, and not overlap.