Add remote session loading

internal/config/config.go

@@ -10,7 +10,8 @@ type Config struct {
 	CampaignPath string
 	SessionPath  string
 
-	StableInputs ResolvedStableInputs
+	StableInputs  ResolvedStableInputs
+	SessionSource SessionSource
 }
 
 // PipelineConfig contains durable pipeline-level settings.
@@ -262,3 +263,14 @@ type ResolvedInputFile struct {
 	ConfigPath string
 	Source     string
 }
+
+// SessionSource records where session.yml came from before materialization.
+type SessionSource struct {
+	Source    string
+	LocalPath string
+	S3Bucket  string
+	S3Key     string
+	S3Size    int64
+	S3ETag    string
+	SpoolPath string
+}