Make delivery asset outcomes disjoint

delivery.go

@@ -49,17 +49,24 @@ type DeliveryRequest struct {
 }
 
 // DeliveryResult reports hosted content and the state reached by this
-// invocation. A partial result may accompany an error.
+// invocation. A partial result may accompany an error. The asset slices are
+// current observations: an asset appears in at most one slice, and early
+// failures may leave some declared assets unreported.
 type DeliveryResult struct {
 	Version         string
 	CandidateCommit string
 	ReleaseURL      string
 	State           DeliveryState
-	Matching        []DeliveryAsset
-	Uploaded        []DeliveryAsset
-	Pending         []DeliveryAsset
-	Conflicting     []DeliveryAsset
-	Uncertain       []DeliveryAsset
+	// Matching lists existing attachments with the declared content.
+	Matching []DeliveryAsset
+	// Uploaded lists assets whose uploads were confirmed during this invocation.
+	Uploaded []DeliveryAsset
+	// Pending lists assets known to be missing.
+	Pending []DeliveryAsset
+	// Conflicting lists assets with detected content conflicts.
+	Conflicting []DeliveryAsset
+	// Uncertain lists assets whose remote state could not be resolved.
+	Uncertain []DeliveryAsset
 }
 
 // Deliver verifies the selected local tag and hosted source, then creates or