Write each module's composition per node, signed, with its digest and the move's judgement beside it (issue 1945, B1)

Every act that sent a declaration now writes compositions instead, by compare-and-set under the lease, and a
module's compositions are kept for its five newest fingerprints and whatever its want or have names (ADR 0539
clauses 1 to 5 and 14). A module the mesh provides itself, which no want can name, rides in the node's own.

internal/broker/composed_test.go

@@ -0,0 +1,49 @@
+package broker
+
+import (
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1945/AC1: a node's composition bucket keeps five revisions of a key and is named for its node; the bucket of digests
+// likewise; a node name a subject would widen is refused.
+func TestTheCompositionBuckets(t *testing.T) {
+	cfg, err := ComposedConfig("ace")
+	if err != nil || cfg.Bucket != "composed-ace" || cfg.History != 5 {
+		t.Fatalf("ComposedConfig(ace) = %+v, %v", cfg, err)
+	}
+	if d := ComposedDigestsConfig(); d.Bucket != delivery.ControllerComposedBucket || d.History != 5 {
+		t.Errorf("ComposedDigestsConfig = %+v", d)
+	}
+	if _, err := ComposedConfig("a.b"); err == nil {
+		t.Errorf("a dotted node got a bucket")
+	}
+}
+
+// 1945/AC1: a node-engine reads its own compositions and its own wants and nothing of another node's, nor the digests;
+// the controller writes a node's bucket by its own subjects.
+func TestANodeReadsOnlyItsOwnCompositions(t *testing.T) {
+	reads, err := ComposedReads("ace")
+	if err != nil {
+		t.Fatal(err)
+	}
+	all := strings.Join(reads, " ")
+	for _, want := range []string{"KV_composed-ace", "$KV.mesh-delivery-assigner_wants.want.ace.>"} {
+		if !strings.Contains(all, want) {
+			t.Errorf("a node-engine of ace cannot reach %s: %v", want, reads)
+		}
+	}
+	for _, never := range []string{"composed-g14", delivery.ControllerComposedBucket, "$KV.composed-ace", "want.*", "want.>"} {
+		if strings.Contains(all, never) {
+			t.Errorf("a node-engine of ace is granted %s: %v", never, reads)
+		}
+	}
+	if w, err := ComposedWrites("ace"); err != nil || w != "$KV.composed-ace.>" {
+		t.Errorf("ComposedWrites(ace) = %q, %v", w, err)
+	}
+	if _, err := ComposedReads("a*"); err == nil {
+		t.Errorf("a node name with a wildcard was granted")
+	}
+}