diff --git a/sdk/buildstep/passing.go b/sdk/buildstep/passing.go
index 8747d747..e3530ce8 100644
--- a/sdk/buildstep/passing.go
+++ b/sdk/buildstep/passing.go
@@ -54,6 +54,12 @@ func PassingCause(words string) bool {
 	return false
 }
 
+// DropKey is the key of an ask's drop in a build seat's pauses state: "dropped.<id>" (the part build-step).
+func DropKey(askID string) string { return "dropped." + askID }
+
+// DroppedPrefix opens every key DropKey makes.
+const DroppedPrefix = "dropped."
+
 // Drop is the value of the key dropped.<ask id> of a build seat's pauses state: an ask its caller no longer waits for.
 type Drop struct {
 	V   int       `json:"v,omitempty"`