A late merge is named however its modules read since the cut; a walk builds the commits it carries (hq ADR 0276 review)

cmd/mesh-controller/plan_retry.go

@@ -197,11 +197,11 @@ func retryRefusal(p inventory.Plan, plans []inventory.Plan) error {
 	return oneWalkAtATime(p, plans)
 }
 
-// oneWalkAtATime refuses a retry while another walk that started is open (novox/hq ADR 0276): a walk retried
-// beside it would be two walks at once.
+// oneWalkAtATime refuses a retry while another walk is open, started or waiting for its word (novox/hq ADR
+// 0276): a walk retried beside it would be two walks at once.
 func oneWalkAtATime(p inventory.Plan, plans []inventory.Plan) error {
 	for _, q := range plans {
-		if q.ID != p.ID && q.Open() && q.Release == nil && !q.Waiting() {
+		if q.ID != p.ID && q.Open() && q.Release == nil {
 			return fmt.Errorf("%s is open (%s): one walk at a time — retry %s once it ended", q.ID, q.Named(), p.ID)
 		}
 	}
@@ -276,6 +276,18 @@ func retryPlan(ctx context.Context, open *stores, id string) (string, error) {
 		return "", err
 	}
 	plans = append(plans, recent...)
+	// **A failed walk whose earlier merges are walked alone is not retried** (novox/hq ADR 0276): the search for
+	// the merge that brought the failure answers them now, and a retried walk would name them twice.
+	if p.Delivery != nil && len(p.Delivery.Merges) > 0 {
+		kept, err := inv.MergesOf(ctx, p.ID)
+		if err != nil {
+			return "", err
+		}
+		if len(kept) < len(p.Delivery.Merges) {
+			return "", fmt.Errorf("%s's earlier merges are walked alone, to find which one brought its failure: "+
+				"those walks answer them; a newer merge, or `rebuild <module>`, builds again", p.ID)
+		}
+	}
 	if err := retryRefusal(p, plans); err != nil {
 		return "", err
 	}