Keep a merge a cut made history, and build a batch's walk at the branch (hq ADR 0276 review)

cmd/mesh-controller/missed_merges.go

@@ -66,6 +66,24 @@ func (u unheardMerges) AnnouncedMerges(ctx context.Context, since time.Time) ([]
 	return out, nil
 }
 
+// owedToTheRecord says a merge read as history is still owed to the record (novox/hq ADR 0276): the merges
+// reader knows, when it keeps them (unheardMerges).
+func owedToTheRecord(ctx context.Context, announced merges, m link.SourceMoved, entries []inventory.Entry,
+	read map[string][]inventory.ReadRepository) bool {
+	u, ok := announced.(unheardMerges)
+	if !ok {
+		return false
+	}
+	merged, err := time.Parse(time.RFC3339Nano, m.MergedAt)
+	if err != nil {
+		return false
+	}
+	raw := m
+	raw.MergedAt = ""
+	owed, err := owedLate(ctx, u.inv, m, merged, wouldMove(raw, entries, read))
+	return err == nil && owed
+}
+
 // catchingUpOnMerges reads back the forge's announcements on a timer, until the context ends.
 func catchingUpOnMerges(ctx context.Context, open *stores, announced merges) {
 	f := following{open}
@@ -136,7 +154,7 @@ func catchUpOnMerges(ctx context.Context, now time.Time, announced merges,
 		if now.Sub(a.At) < mergeGrace {
 			continue
 		}
-		if len(wouldMove(a.SourceMoved, entries, read)) == 0 {
+		if len(wouldMove(a.SourceMoved, entries, read)) == 0 && !owedToTheRecord(ctx, announced, a.SourceMoved, entries, read) {
 			continue
 		}
 		if entries, read, err = catalogued(ctx); err != nil {
@@ -144,7 +162,12 @@ func catchUpOnMerges(ctx context.Context, now time.Time, announced merges,
 		}
 		moves := wouldMove(a.SourceMoved, entries, read)
 		if len(moves) == 0 {
-			continue
+			if !owedToTheRecord(ctx, announced, a.SourceMoved, entries, read) {
+				continue
+			}
+			raw := a.SourceMoved
+			raw.MergedAt = ""
+			moves = wouldMove(raw, entries, read)
 		}
 		var names []string
 		for _, e := range moves {