Add transcript passthrough processing

internal/core/io/files.go

@@ -0,0 +1,29 @@
+package io
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+func ReadRequiredFile(path string, label string) ([]byte, error) {
+	contents, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read %s file %q: %w", label, path, err)
+	}
+	return contents, nil
+}
+
+func ValidateWellFormedJSON(raw []byte) error {
+	if !json.Valid(raw) {
+		return fmt.Errorf("transcript file is not valid JSON")
+	}
+	return nil
+}
+
+func WriteFile(path string, contents []byte) error {
+	if err := os.WriteFile(path, contents, 0o644); err != nil {
+		return fmt.Errorf("failed to write output file %q: %w", path, err)
+	}
+	return nil
+}