Trim and validate scene caveats

internal/modules/chunk/dnd/scenes/chunker.go

@@ -99,13 +99,17 @@ func (c *Chunker) Chunk(ctx context.Context, req contracts.ChunkRequest) (contra
 		return contracts.ChunkResult{}, chunkerErrorf("complete structured output: %w", err)
 	}
 
+	warnings, err := warningsFromCaveats(response.BoundaryCaveats)
+	if err != nil {
+		return contracts.ChunkResult{}, chunkerErrorf("malformed structured output: %w", err)
+	}
 	chunks, err := chunksFromResponse(req.Source, response)
 	if err != nil {
 		return contracts.ChunkResult{}, chunkerErrorf("malformed structured output: %w", err)
 	}
 	return contracts.ChunkResult{
 		Chunks:   chunks,
-		Warnings: warningsFromCaveats(response.BoundaryCaveats),
+		Warnings: warnings,
 	}, nil
 }
 
@@ -259,19 +263,23 @@ func validBoundaryConfidence(value string) bool {
 	}
 }
 
-func warningsFromCaveats(caveats []string) []contracts.Warning {
+func warningsFromCaveats(caveats []string) ([]contracts.Warning, error) {
 	if len(caveats) == 0 {
-		return nil
+		return nil, nil
 	}
 	warnings := make([]contracts.Warning, 0, len(caveats))
-	for _, caveat := range caveats {
+	for i, caveat := range caveats {
+		trimmed := strings.TrimSpace(caveat)
+		if trimmed == "" {
+			return nil, fmt.Errorf("boundary_caveats[%d] must not be empty after trimming", i)
+		}
 		warnings = append(warnings, contracts.Warning{
 			Scope:      Key,
 			ReasonCode: "scene_boundary_caveat",
-			Message:    caveat,
+			Message:    trimmed,
 		})
 	}
-	return warnings
+	return warnings, nil
 }
 
 func cloneUnits(units []source.SourceUnit) []source.SourceUnit {