Keep the builds every want names and each composition's provisioner plans; find the replaced controller in the build records (issue 1945)

With no plan left to name a build or a send to keep the plans, a want names what a collection must keep, and the
composition is where the provisioner's plans are composed for the assignments mirror (ADR 0539 clauses 1 and 5);
the assignments no longer name a node's build, so the controller replaced is the newest earlier build of it.

cmd/mesh-controller/composed_start_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/inventory"
 )
 
 // fakeBuckets is the bus's buckets by name, for deleting.
@@ -70,3 +71,23 @@ func TestTheReplacedControllerIsComposedFromItsOwnManifest(t *testing.T) {
 		t.Errorf("composing the replaced controller changed the Input's catalogue")
 	}
 }
+
+// 1945/AC6 (unit half): the controller replaced is the newest earlier build of the controller that worked and names a
+// fingerprint of the new form, not the one registered now.
+func TestTheReplacedControllerIsItsNewestEarlierBuild(t *testing.T) {
+	now, before, older := sdkdelivery.SourcePrefix2+strings.Repeat("6", 64), sdkdelivery.SourcePrefix2+strings.Repeat("5", 64),
+		sdkdelivery.SourcePrefix2+strings.Repeat("4", 64)
+	m := []byte(`{"module":"mesh-controller","version":"5"}`)
+	builds := []inventory.Build{
+		{ID: "c6", SourceFingerprint: now, Manifest: m},
+		{ID: "c5-failed", SourceFingerprint: before, Failed: "no", Manifest: m},
+		{ID: "c5", SourceFingerprint: before, Manifest: m},
+		{ID: "c4", SourceFingerprint: older, Manifest: m},
+	}
+	if b, ok := replacedBuild(builds, now); !ok || b.ID != "c5" {
+		t.Errorf("the replaced build is %+v (%v), want c5", b, ok)
+	}
+	if _, ok := replacedBuild(builds[:1], now); ok {
+		t.Errorf("a controller with no earlier build replaced one")
+	}
+}