Let a want held back at an earlier fingerprint follow that fingerprint's new revision (issue 1945, ADR 0545)

The controller now composes a module's kept compositions again when its config
changes, so going back keeps today's config. A want held back at an earlier
fingerprint kept the digest it was first written with, and the node applied
the old revision from the bucket's history: on g14 a rollback of mesh-build-go
put its capacity back to 0. The want now names the new digest, asked through
the record hold as any move of a record module is. A want held at F by the
rules still waits for them, as a new fingerprint does (ADR 0539 §5).
Research 072: milestone 2, the composer reacting to the change of an input.

modules/mesh-delivery-assigner/internal/assign/wants.go

@@ -307,7 +307,22 @@ func Wants(m Module, n Nodes, wants map[string]delivery.Want, lastHealthy map[st
 			}
 			next = delivery.Want{FP: before.FP, Composed: before.Composed, Newest: m.FP, Rule: rule, Words: words}
 			if before.FP == m.FP {
+				// Held at F by the rules: a new revision of F's composition waits for them, as a new fingerprint does (ADR 0539 §5).
 				next = delivery.Want{FP: m.FP, Composed: before.Composed}
+			} else if d, there := m.composition(node, before.FP); there && d.Digest != "" && d.Digest != before.Composed {
+				// Held back at an earlier fingerprint whose kept composition the controller composed again with today's config
+				// (novox/hq ADR 0545): the want follows its new revision, so the node does not run that build with the config of
+				// the moment it was made (on g14 a capacity of 0 after a rollback). Asked as any move of a record module is.
+				at := m
+				at.FP = before.FP
+				running, ran := n.Haves[node][m.Name]
+				need, wait := at.mustAsk(node, before, true, ran, running.FP, running.Composed == "", d)
+				if need != nil {
+					out.Record = append(out.Record, *need)
+				}
+				if !wait {
+					next.Composed = d.Digest
+				}
 			}
 		}
 		if !had || !delivery.SameWant(normal(before), normal(next)) {

modules/mesh-delivery-assigner/internal/assign/wants_test.go

@@ -221,6 +221,25 @@ func TestARevisionAtTheSameFingerprintIsAWantByTheSameRules(t *testing.T) {
 	if w, ok := out.Wants["ace"]; ok && w.Composed == revised {
 		t.Errorf("a revision was written while a rule holds: %+v", w)
 	}
+
+	// A want held back at an earlier fingerprint follows the new revision of that fingerprint's kept composition, which the
+	// controller composed again with today's config (novox/hq ADR 0545: on g14 a capacity of 0 after a rollback), while
+	// the rules still hold F; for a record module whose revision recreates a container, only after the ask.
+	out = Wants(m, n, wantedOld(), nil)
+	if w := out.Wants["g14"]; w.FP != fOld || w.Composed != revised || w.Newest != fNew {
+		t.Errorf("g14, held back at its earlier fingerprint, wants %+v; want it at that fingerprint naming the revised digest", w)
+	}
+	m.Composed = func(node, fp string) (delivery.ComposedDigest, bool) {
+		return delivery.ComposedDigest{Digest: revised, Judgement: delivery.JudgedRecreates, Policy: delivery.PolicyRecord,
+			Against: dig(fOld), Words: "recreates"}, true
+	}
+	out = Wants(m, n, wantedOld(), nil)
+	if w := out.Wants["g14"]; w.Composed == revised {
+		t.Errorf("a recorded module's revision that recreates a container was written with no ask: %+v", w)
+	}
+	if !slices.ContainsFunc(out.Record, func(r RecordNeed) bool { return r.Node == "g14" && r.Digest == revised }) {
+		t.Errorf("the revision was not asked: %+v", out.Record)
+	}
 }
 
 // 1906/D2: a set-back names the composition of the fingerprint it sets back to, and when that is gone the want stays and says so.