Remove the five-minute merge catch-up, its signal S5 and its watchdog: the event and its durable consumer keep every merge (issue 973)

cmd/mesh-controller/batches.go

@@ -67,6 +67,10 @@ const mergeWindowFileVar = "MESH_MERGE_WINDOW_FILE"
 // the controller is said to have failed to cut it (ADR 0276 decision 9).
 const batchLateAfter = time.Minute
 
+// mergeGrace is how long before a batch's first merge a merge may have been made and still be told apart from one
+// made before the controller began keeping merges (owedLate).
+const mergeGrace = 10 * time.Minute
+
 // edgeGroupOrder is a delivery group's order made an edge of a walk's tiers (ADR 0276 decision 5): the
 // modules of the member after depend on the modules of the member before, and are gated on them.
 const edgeGroupOrder = "group-order"
@@ -124,8 +128,7 @@ func durationSetting(v any) (time.Duration, bool) {
 // hearMerge puts a merge the forge announced into the batch that answers it, at the moment it was heard,
 // and cuts what is due.
 func (f following) hearMerge(ctx context.Context, m link.SourceMoved, now time.Time) error {
-	// One merge acted on at a time, whoever hands it over: the bus, or the catch-up that reads back
-	// what the bus did not hand over (novox/hq issue 266).
+	// One merge acted on at a time, whoever hands it over (novox/hq issue 266).
 	actingOnMerges.Lock()
 	defer actingOnMerges.Unlock()
 
@@ -244,7 +247,7 @@ func (f following) hearMerge(ctx context.Context, m link.SourceMoved, now time.T
 }
 
 // owedLate says a merge that reads as history is still the record's to answer (review of this change): a cut
-// marks every module it moved seen at that moment, so a merge of that branch the bus lost and the catch-up
+// marks every module it moved seen at that moment, so a merge of that branch handed over late
 // hands over later — made before the cut, heard after it — reads as history and was dropped. One that touches
 // a module the mesh holds, of a branch whose merges the controller keeps, made since it began keeping them,
 // is kept; one made before it began is old news, as before.