D7a: the assigner, the indexer and the builder ask a node's manifest-reads once before the kept call, so a node that answers nothing reads as its fallback at once (issue 1966, ADR 0668 §3; review round 1, finding 1)

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/main.go

@@ -317,6 +317,7 @@ func follow(ctx context.Context, js jetstream.JetStream, nc process.Subscriber,
 	reads := &enginereads.Keeper{Fallback: w.recordReads, Changed: wake, Logf: logger.Printf}
 	if bus != nil {
 		reads.Call = bus.CallKeptOn // a kept call, called again through a transport fault (ADR 0668 §1)
+		reads.Once = bus.CallOn     // its fault keeps the fallback at once while the kept call asks on (ADR 0668 §3)
 	}
 	if kv := kvs[engineReadsBucket]; kv != nil {
 		reads.Put = func(node string, v []byte) error { _, err := kv.Put(ctx, node, v); return err }

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go

@@ -270,6 +270,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	// What each counted node's engine reads (ADR 0618 §2, ADR 0624 §1): asked through the node-engine seat's verb as the
 	// builder's own account, for every node the assignments names, and kept in the state engine-reads once it is bound.
 	reads := newEngineReads(calls.CallKeptOn, gate, logger.Printf)
+	reads.keeper.Once = calls.CallOn // its fault keeps the last statement at once while the kept call asks on (ADR 0668 §3)
 	// The old reference form's window over them (DLV-B9), kept in the state old-form once it is bound; builder_old_form
 	// reads it and drops a retired node by hand.
 	reads.ctx = context.WithoutCancel(ctx)

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/main.go

@@ -493,6 +493,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	// §2): asked through the node-engine seat's verb as the indexer's own account, for every node the assignments names,
 	// kept in the state engine-reads once it is bound; each change weighs the holds again.
 	reads := newEngineReads(calls.CallKeptOn, gate, func() { ix.KickHolds(ctx) }, logger.Printf)
+	reads.keeper.Once = calls.CallOn // its fault keeps the last statement at once while the kept call asks on (ADR 0668 §3)
 	gate.OnPlaced = reads.placed
 	ix.Counted, ix.AskEngines = reads.counted, reads.ask
 	// The holds, new with ADR 0632 (issue 1790's kind), bound when they appear: until then a merge that would hold a