Owe a merge to the record from its branch's first kept merge (hq ADR 0276 review)

internal/inventory/batches.go

@@ -64,15 +64,13 @@ func (i *Inventory) LaterMergesOf(ctx context.Context, repository, branch string
 		order by merged_at desc`, repository, branch, after)
 }
 
-// KeptOnBranch says the controller keeps a merge of a repository's branch, and when it heard its first merge
-// of any: a merge of a branch it keeps merges of, made since then, is the record's to answer, whatever a
+// KeptOnBranch says the controller keeps a merge of a repository's branch, and when it heard the branch's first: a merge of a branch it keeps merges of, made since then, is the record's to answer, whatever a
 // module's last look says (novox/hq ADR 0276).
 func (i *Inventory) KeptOnBranch(ctx context.Context, repository, branch string) (bool, time.Time, error) {
 	var first *time.Time
 	var kept bool
 	err := i.store.Pool().QueryRow(ctx,
-		`select (select min(heard_at) from batched_merge),
-		        exists (select 1 from batched_merge where repository = lower($1) and branch = $2)`,
+		`select min(heard_at), count(*) > 0 from batched_merge where repository = lower($1) and branch = $2`,
 		repository, branch).Scan(&first, &kept)
 	if err != nil || first == nil {
 		return false, time.Time{}, err