Implement integer source units and chunk payloads

internal/modules/chunk/generic/chunker.go

@@ -68,11 +68,19 @@ func (c *Chunker) Chunk(ctx context.Context, req contracts.ChunkRequest) (contra
 			end = len(req.Source.Units)
 		}
 		units := cloneUnits(req.Source.Units[start:end])
+		content, err := chunkContent(units)
+		if err != nil {
+			return contracts.ChunkResult{}, err
+		}
 		chunks = append(chunks, contracts.SourceChunk{
-			ID:       fmt.Sprintf("chunk-%06d", len(chunks)+1),
-			SourceID: req.Source.ID,
-			Index:    len(chunks),
-			Units:    units,
+			ID:          fmt.Sprintf("chunk-%06d", len(chunks)+1),
+			SourceID:    req.Source.ID,
+			Index:       len(chunks),
+			StartUnitID: units[0].ID,
+			EndUnitID:   units[len(units)-1].ID,
+			Content:     content,
+			MediaType:   "application/json",
+			Units:       units,
 			Metadata: map[string]any{
 				"start_unit_id": units[0].ID,
 				"end_unit_id":   units[len(units)-1].ID,
@@ -87,6 +95,18 @@ func (c *Chunker) Chunk(ctx context.Context, req contracts.ChunkRequest) (contra
 	return contracts.ChunkResult{Chunks: chunks}, nil
 }
 
+func chunkContent(units []source.SourceUnit) ([]byte, error) {
+	content, err := json.Marshal(struct {
+		Units []source.SourceUnit `json:"units"`
+	}{
+		Units: units,
+	})
+	if err != nil {
+		return nil, chunkerErrorf("encode chunk content: %w", err)
+	}
+	return content, nil
+}
+
 func ModuleSpec() pipeline.ModuleSpec {
 	return pipeline.ModuleSpec{
 		Key:      Key,