Centralize D&D extraction request preparation

internal/modules/dnd/shared/extraction_inputs.go

@@ -2,14 +2,30 @@ package shared
 
 import (
 	"bytes"
+	"context"
 	"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) {
+// PrepareChunkExtraction validates common D&D extraction prerequisites and
+// prepares owned chunk-scoped source material for prompt inputs.
+func PrepareChunkExtraction(ctx context.Context, req contracts.TypedExtractionRequest) (contracts.LLMInputMaterial, error) {
+	if ctx == nil {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("context must not be nil")
+	}
+	if err := ctx.Err(); err != nil {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("context error before extraction: %w", err)
+	}
+	if req.Source == nil {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("source must not be nil")
+	}
+	if req.Chunk == nil {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("chunk must not be nil")
+	}
+	if len(req.Chunk.Units) == 0 {
+		return contracts.LLMInputMaterial{}, fmt.Errorf("chunk %q units must not be empty", req.Chunk.ID)
+	}
 	material := req.SourceInput.Clone()
 	if len(material.Content) == 0 {
 		material = contracts.NewLLMInputMaterial("source", req.Chunk.MediaType, req.Chunk.Content, "", "")