Centralize D&D chunk prompt material preparation

internal/modules/dnd/shared/extraction_inputs.go

@@ -0,0 +1,30 @@
+package shared
+
+import (
+	"bytes"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
+)
+
+// ChunkPromptMaterial prepares the chunk-scoped source material used by D&D
+// extractors when constructing their prompt inputs.
+func ChunkPromptMaterial(req contracts.TypedExtractionRequest) (contracts.LLMInputMaterial, error) {
+	material := req.SourceInput.Clone()
+	if len(material.Content) == 0 {
+		material = contracts.NewLLMInputMaterial("source", req.Chunk.MediaType, req.Chunk.Content, "", "")
+	}
+	if !bytes.Equal(material.Content, req.Chunk.Content) {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("source input must match chunk %q content", req.Chunk.ID)
+	}
+	if material.Name == "" {
+		material.Name = "source"
+	}
+	if material.MediaType == "" {
+		material.MediaType = req.Chunk.MediaType
+	}
+	if material.SizeBytes == 0 {
+		material.SizeBytes = int64(len(material.Content))
+	}
+	return material, nil
+}