issue 1840/S3: keep each node's declared packages on the bus, so the pacman verbs can say what a node declares

cmd/mesh-controller/declared_packages_integration_test.go

@@ -0,0 +1,61 @@
+//go:build integration
+
+package main
+
+import (
+	"encoding/json"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// 1840/AC5 (ADR 0507 §5): the source of the declared-packages mirror composes each node and names, for a package two modules
+// declare and one declared absent, the modules that declare it; the same records give the same bytes on a second pass, so
+// the mirror writes nothing; a node with no package has a key that says so.
+func TestTheDeclaredPackagesMirrorNamesWhatEachNodesModulesDeclare(t *testing.T) {
+	open := aMesh(t)
+	ctx := t.Context()
+	register(t, open, catalogue.Manifest{Module: "viewer", Version: "1", Resources: []map[string]any{
+		{"id": "pkg-curl", "type": "package", "package": "curl"},
+		{"id": "pkg-nano", "type": "package", "package": "nano", "absent": true}}})
+	register(t, open, catalogue.Manifest{Module: "fetcher", Version: "1", Resources: []map[string]any{
+		{"id": "pkg-curl", "type": "package", "package": "curl"}}})
+	for _, module := range []string{"viewer", "fetcher"} {
+		if _, err := assign(ctx, open, "anchor", module); err != nil {
+			t.Fatalf("assign anchor %s: %v", module, err)
+		}
+	}
+	source := declaredPackagesMirror(open)
+	first, err := source(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got inventory.DeclaredPackagesMirrored
+	if err := json.Unmarshal(first["anchor"], &got); err != nil {
+		t.Fatalf("anchor has no value: %v", err)
+	}
+	want := []inventory.PackageDeclared{{Package: "curl", Modules: []string{"fetcher", "viewer"}},
+		{Package: "nano", Modules: []string{"viewer"}, Absent: true}}
+	if len(got.Packages) != len(want) {
+		t.Fatalf("anchor declares %+v, want %+v", got.Packages, want)
+	}
+	for i, p := range want {
+		if g := got.Packages[i]; g.Package != p.Package || g.Absent != p.Absent || len(g.Modules) != len(p.Modules) ||
+			(len(p.Modules) > 0 && g.Modules[0] != p.Modules[0]) {
+			t.Errorf("package %d is %+v, want %+v", i, g, p)
+		}
+	}
+	if string(first["laptop"]) != `{"node":"laptop","packages":[]}` {
+		t.Errorf("a node declaring none is %s", first["laptop"])
+	}
+	second, err := source(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for node, value := range first {
+		if string(second[node]) != string(value) {
+			t.Errorf("the value of %s changed between two passes over the same records:\n%s\n%s", node, value, second[node])
+		}
+	}
+}

cmd/mesh-controller/push.go

@@ -281,7 +281,7 @@ func serve(ctx context.Context) (err error) {
 	// The provisioner's plan of each handed module, as its machine was last sent it (design 57 P6), in the module's
 	// assignment.
 	inv.SetProvisioningPlans(inv.SentProvisioningPlans)
-	go mirroringRecords(ctx, inv, bus.Conn, bus)
+	go mirroringRecords(ctx, open, inv, bus.Conn, bus)
 	// And the bucket of the files that travel by digest, judged against what each machine's latest declaration names (ADR 0486 §3).
 	go sweepingDeclarationFiles(ctx, inv, bus.Conn)
 	// And the key of each plan in its build phase, which holds the build seat's checks while a delivery builds (ADR 0483 clause 2).

cmd/mesh-controller/record_mirrors.go

@@ -7,6 +7,7 @@ import (
 	"sort"
 	"time"
 
+	"git.novox.be/novox/mesh-sdk/go/compose"
 	"github.com/nats-io/nats.go"
 	"github.com/nats-io/nats.go/jetstream"
 
@@ -29,7 +30,7 @@ import (
 const mirrorEvery = 10 * time.Second
 
 // mirroringRecords keeps the mirrors current for as long as this controller serves: ctx ends when it stops.
-func mirroringRecords(ctx context.Context, inv *inventory.Inventory, conn *nats.Conn, announce recordmirror.Announcer) {
+func mirroringRecords(ctx context.Context, open *stores, inv *inventory.Inventory, conn *nats.Conn, announce recordmirror.Announcer) {
 	api, err := jetstream.New(conn)
 	if err != nil {
 		fmt.Printf("the record mirrors are not kept: %v\n", err)
@@ -44,8 +45,9 @@ func mirroringRecords(ctx context.Context, inv *inventory.Inventory, conn *nats.
 		return e
 	}
 	sources := map[string]func(context.Context) (map[string][]byte, error){
-		recordmirror.DeclaredConfig.Name: inv.DeclaredConfigMirror,
-		recordmirror.Predefined.Name:     inv.PredefinedMirror,
+		recordmirror.DeclaredConfig.Name:   inv.DeclaredConfigMirror,
+		recordmirror.Predefined.Name:       inv.PredefinedMirror,
+		recordmirror.DeclaredPackages.Name: declaredPackagesMirror(open),
 	}
 	writers := map[string]*recordmirror.Writer{}
 	failing := map[string]string{}
@@ -176,3 +178,36 @@ func keepingAssignments(ctx context.Context, inv *inventory.Inventory, announce
 	}
 	events.known = now
 }
+
+// declaredPackagesMirror is the source of the declared-packages mirror (ADR 0507 §5): each node's composition, asked as a
+// question that makes nothing, and the packages it declares with the modules that declare them. A node whose own set does
+// not compose has no key, and any other failure to read is the pass's error, so a key is never purged for a store that
+// could not be read.
+func declaredPackagesMirror(open *stores) func(context.Context) (map[string][]byte, error) {
+	return func(ctx context.Context) (map[string][]byte, error) {
+		in, err := inputFor(ctx, open)
+		if err != nil {
+			return nil, err
+		}
+		// Which module owns each resource is carried only for a node-engine that reads it, so every node is asked as one that does.
+		asked := in.Input
+		asked.Nodes = append([]compose.Node(nil), in.Nodes...)
+		for i := range asked.Nodes {
+			asked.Nodes[i].ReadsModules = true
+		}
+		out := map[string][]byte{}
+		for _, n := range in.sortedNodes() {
+			d, _, err := compose.ComposeIn(asked, n.Name, compose.Foreseeing)
+			if compose.IsUnresolvable(err) {
+				continue
+			}
+			if err != nil {
+				return nil, fmt.Errorf("the packages %s declares cannot be read: %w", n.Name, err)
+			}
+			if out[n.Name], err = inventory.DeclaredPackagesValue(n.Name, d.Resources, d.ModuleOf); err != nil {
+				return nil, err
+			}
+		}
+		return out, nil
+	}
+}

internal/broker/controller_buckets.go

@@ -104,6 +104,9 @@ var (
 	AssignmentsBucket    = BucketName(ControllerSeat, MirrorAssignments)
 	DeclaredConfigBucket = BucketName(ControllerSeat, MirrorDeclaredConfig)
 	PredefinedBucket     = BucketName(ControllerSeat, MirrorPredefined)
+	// DeclaredPackagesBucket holds, keyed by the node, each package the modules assigned to it declare, present or absent,
+	// with the declaring modules: what the pacman module's verbs read to say a package is declared (ADR 0507 §5).
+	DeclaredPackagesBucket = BucketName(ControllerSeat, MirrorDeclaredPackages)
 )
 
 // The mirrors' local names, as a reader names them in `reads` after `mesh-controller.`.
@@ -111,6 +114,8 @@ const (
 	MirrorAssignments    = "assignments"
 	MirrorDeclaredConfig = "declared-config"
 	MirrorPredefined     = "predefined"
+	// MirrorDeclaredPackages is the local name of the packages each node's modules declare (ADR 0507 §5, issue 1840/S3).
+	MirrorDeclaredPackages = "declared-packages"
 )
 
 // The chain's buckets (novox/hq ADR 0408, issue 1089): builds, rollouts and assignments are one chain kept on the bus
@@ -153,7 +158,7 @@ func ChainBuckets() []string { return []string{BuildsBucket, RolloutsBucket, Ass
 // ControllerMirrors are the local names of the controller's buckets a module may read: the record mirrors and the
 // chain's buckets.
 func ControllerMirrors() []string {
-	return []string{MirrorAssignments, MirrorDeclaredConfig, MirrorPredefined, ChainBuilds, ChainRollouts, ChecksRunning, PlansBuilding}
+	return []string{MirrorAssignments, MirrorDeclaredConfig, MirrorPredefined, ChainBuilds, ChainRollouts, ChecksRunning, PlansBuilding, MirrorDeclaredPackages}
 }
 
 // MirrorsWrittenByAnother are the controller's mirrors whose writer is not the controller, each with its reason: the rule
@@ -222,6 +227,7 @@ func IsControllerBucket(bucket string) bool {
 	return bucket == CallsBucket || bucket == HandActsBucket || bucket == ConditionsBucket ||
 		bucket == ConditionHistoryBucket || bucket == LeaseBucket || bucket == AskedBucket ||
 		bucket == AssignmentsBucket || bucket == DeclaredConfigBucket || bucket == PredefinedBucket ||
+		bucket == DeclaredPackagesBucket ||
 		bucket == MergeWindowBucket || bucket == RolloutSilentBucket || bucket == CheckRunningBucket ||
 		bucket == DeliveryMergesBucket || bucket == BuildsBucket || bucket == RolloutsBucket ||
 		bucket == PlansBuildingBucket || bucket == delivery.HaveBucket
@@ -230,7 +236,7 @@ func IsControllerBucket(bucket string) bool {
 // ControllerBuckets are the controller's own buckets, in the order they are asserted.
 func ControllerBuckets() []string {
 	return []string{LeaseBucket, CallsBucket, HandActsBucket, ConditionsBucket, ConditionHistoryBucket, AskedBucket,
-		AssignmentsBucket, DeclaredConfigBucket, PredefinedBucket, MergeWindowBucket, RolloutSilentBucket, CheckRunningBucket,
+		AssignmentsBucket, DeclaredConfigBucket, PredefinedBucket, DeclaredPackagesBucket, MergeWindowBucket, RolloutSilentBucket, CheckRunningBucket,
 		DeliveryMergesBucket, PlansBuildingBucket, BuildsBucket, RolloutsBucket, delivery.HaveBucket}
 }
 
@@ -446,6 +452,9 @@ func (j *JetStream) EnsureControllerBuckets() error {
 		{PredefinedBucket, "the list of predefined keys the mesh published, the newest trunk build's of the " +
 			"catalogue, one key `list` (novox/hq ADR 0348 §7, design 57 K3): written by the controller alone from " +
 			"its store when a newer list is kept, read through `reads`"},
+		{DeclaredPackagesBucket, "each package the modules assigned to a node declare, present or absent, with the " +
+			"declaring modules, keyed by the node (novox/hq ADR 0507 §5): written by the controller alone when it " +
+			"composes the node, only on a change, read through `reads`"},
 	} {
 		if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
 			Bucket:         m.bucket,

internal/broker/declared_packages_mirror_test.go

@@ -0,0 +1,41 @@
+package broker
+
+import (
+	"slices"
+	"testing"
+)
+
+// Issue 1840/S3 (ADR 0507 §5), 1840/AC5: a module whose manifest reads mesh-controller.declared-packages may name it in
+// `reads`, and reads the bucket and writes none; the controller writes it, so it is no mirror written by another, and it is
+// one of the controller's own buckets, asserted at its start.
+func TestAModuleReadingDeclaredPackagesReadsAndWritesNone(t *testing.T) {
+	if !slices.Contains(ControllerMirrors(), "declared-packages") ||
+		BucketName(ControllerSeat, MirrorDeclaredPackages) != DeclaredPackagesBucket {
+		t.Fatalf("a module cannot name %s in `reads`: %v", DeclaredPackagesBucket, ControllerMirrors())
+	}
+	if _, other := MirrorsWrittenByAnother[MirrorDeclaredPackages]; other {
+		t.Error("the controller writes the declared packages itself")
+	}
+	if !IsControllerBucket(DeclaredPackagesBucket) || !slices.Contains(ControllerBuckets(), DeclaredPackagesBucket) {
+		t.Errorf("%s is not among the controller's buckets", DeclaredPackagesBucket)
+	}
+	perms, err := PermissionsFor(Principal{Kind: KindModule, Node: "one", Module: "pacman", PasswordHash: "x",
+		Reads: []string{"mesh-controller.declared-packages"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	stream := "KV_" + DeclaredPackagesBucket
+	has(t, perms.Publish, "$JS.API.STREAM.INFO."+stream)
+	has(t, perms.Publish, "$JS.API.DIRECT.GET."+stream+".>")
+	has(t, perms.Publish, "$JS.API.CONSUMER.CREATE."+stream+".>")
+	for _, p := range perms.Publish {
+		if SubjectsOverlap(p, "$KV."+DeclaredPackagesBucket+".one") {
+			t.Errorf("the reading module may write %s through %q", DeclaredPackagesBucket, p)
+		}
+	}
+	controller, err := PermissionsFor(Principal{Kind: KindController, PasswordHash: "x"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	has(t, controller.Publish, "$KV."+DeclaredPackagesBucket+".>")
+}

internal/broker/nats.go

@@ -429,6 +429,11 @@ var DegradableGrants = []DegradableGrant{
 		Reason: "refused: the controller then says no plan builds, and no check is held while a delivery builds — a check run " +
 			"wrongly costs a delivery a place, a check held wrongly costs a pull request its turn (ADR 0483 clause 2, issue 1687)",
 	},
+	{
+		Subject: "$KV." + DeclaredPackagesBucket + ".>",
+		Reason: "carried only at genesis: the controller composes its own permissions and pushes them to the bus at its " +
+			"first push, and keeps the packages each node declares only after that, holding the lease (ADR 0507 §5, issue 1840)",
+	},
 	{
 		Subject: "mesh.seat." + ControllerSeat + ".event.sent",
 		Reason: "refused: the controller says a tier sent to a machine only for outsiders, and a send that could not " +

internal/broker/testdata/composed.conf

@@ -29,7 +29,7 @@ accounts {
     ]
     users = [
       { user: "controller", password: "$2a$11$cccccccccccccccccccccc", permissions: {
-        publish: { allow: ["$JS.ACK.CONTROL.controller.>", "$JS.ACK.DEAD_LETTER_NOTICES.controller.>", "$JS.ACK.EVENTS.controller-merges.>", "$JS.ACK.EVENTS.controller.>", "$JS.API.>", "$KV.SEAT_MESH_BUILD_MACHINE_cancelled.>", "$KV.SEAT_NODE_BUILD_AGENT_cancelled.>", "$KV.mesh-controller_asked.>", "$KV.mesh-controller_assignments.>", "$KV.mesh-controller_builds.>", "$KV.mesh-controller_calls.>", "$KV.mesh-controller_checks-running.>", "$KV.mesh-controller_condition-history.>", "$KV.mesh-controller_conditions.>", "$KV.mesh-controller_declared-config.>", "$KV.mesh-controller_delivery-merges.>", "$KV.mesh-controller_hand-acts.>", "$KV.mesh-controller_lease.>", "$KV.mesh-controller_merge-window.>", "$KV.mesh-controller_plans-building.>", "$KV.mesh-controller_predefined.>", "$KV.mesh-controller_rollout-silent.>", "$KV.mesh-controller_rollouts.>", "$SRV.INFO", "_INBOX.enrol.>", "mesh.again.>", "mesh.assignment.>", "mesh.events.dead.>", "mesh.mod.*.tool.>", "mesh.node.>", "mesh.seat.mesh-build-machine.accept.>", "mesh.seat.mesh-build-machine.tool.>", "mesh.seat.mesh-controller.event.applied", "mesh.seat.mesh-controller.event.assignment-changed", "mesh.seat.mesh-controller.event.built-before", "mesh.seat.mesh-controller.event.checked", "mesh.seat.mesh-controller.event.condition-changed", "mesh.seat.mesh-controller.event.condition-cleared", "mesh.seat.mesh-controller.event.condition-raised", "mesh.seat.mesh-controller.event.declared-config-changed", "mesh.seat.mesh-controller.event.doctor-heartbeat", "mesh.seat.mesh-controller.event.healer-acted", "mesh.seat.mesh-controller.event.plan-moved", "mesh.seat.mesh-controller.event.predefined-changed", "mesh.seat.mesh-controller.event.refused", "mesh.seat.mesh-controller.event.rolled-back", "mesh.seat.mesh-controller.event.secret-replaced", "mesh.seat.mesh-controller.event.sent", "mesh.seat.mesh-controller.tool.plans", "mesh.seat.mesh-controller.tool.push", "mesh.seat.mesh-controller.tool.upgrade", "mesh.seat.mesh-delivery.tool.close", "mesh.seat.mesh-delivery.tool.groups", "mesh.seat.mesh-delivery.tool.release", "mesh.seat.mesh-delivery.tool.stalled", "mesh.seat.mesh-delivery.tool.stop", "mesh.seat.mesh-delivery.tool.times", "mesh.seat.node-backup.tool.backed-up.*", "mesh.seat.node-backup.tool.now.*", "mesh.seat.node-build-agent.accept.>", "mesh.seat.node-build-agent.check.>", "mesh.seat.node-build-agent.tool.>", "mesh.seat.node-intrusion-prevention.tool.banned.*", "mesh.seat.node-launcher.tool.secret.*", "mesh.seat.node-service-manager.tool.restart.*", "mesh.seat.operator-channel.tool.tell"] }
+        publish: { allow: ["$JS.ACK.CONTROL.controller.>", "$JS.ACK.DEAD_LETTER_NOTICES.controller.>", "$JS.ACK.EVENTS.controller-merges.>", "$JS.ACK.EVENTS.controller.>", "$JS.API.>", "$KV.SEAT_MESH_BUILD_MACHINE_cancelled.>", "$KV.SEAT_NODE_BUILD_AGENT_cancelled.>", "$KV.mesh-controller_asked.>", "$KV.mesh-controller_assignments.>", "$KV.mesh-controller_builds.>", "$KV.mesh-controller_calls.>", "$KV.mesh-controller_checks-running.>", "$KV.mesh-controller_condition-history.>", "$KV.mesh-controller_conditions.>", "$KV.mesh-controller_declared-config.>", "$KV.mesh-controller_declared-packages.>", "$KV.mesh-controller_delivery-merges.>", "$KV.mesh-controller_hand-acts.>", "$KV.mesh-controller_lease.>", "$KV.mesh-controller_merge-window.>", "$KV.mesh-controller_plans-building.>", "$KV.mesh-controller_predefined.>", "$KV.mesh-controller_rollout-silent.>", "$KV.mesh-controller_rollouts.>", "$SRV.INFO", "_INBOX.enrol.>", "mesh.again.>", "mesh.assignment.>", "mesh.events.dead.>", "mesh.mod.*.tool.>", "mesh.node.>", "mesh.seat.mesh-build-machine.accept.>", "mesh.seat.mesh-build-machine.tool.>", "mesh.seat.mesh-controller.event.applied", "mesh.seat.mesh-controller.event.assignment-changed", "mesh.seat.mesh-controller.event.built-before", "mesh.seat.mesh-controller.event.checked", "mesh.seat.mesh-controller.event.condition-changed", "mesh.seat.mesh-controller.event.condition-cleared", "mesh.seat.mesh-controller.event.condition-raised", "mesh.seat.mesh-controller.event.declared-config-changed", "mesh.seat.mesh-controller.event.doctor-heartbeat", "mesh.seat.mesh-controller.event.healer-acted", "mesh.seat.mesh-controller.event.plan-moved", "mesh.seat.mesh-controller.event.predefined-changed", "mesh.seat.mesh-controller.event.refused", "mesh.seat.mesh-controller.event.rolled-back", "mesh.seat.mesh-controller.event.secret-replaced", "mesh.seat.mesh-controller.event.sent", "mesh.seat.mesh-controller.tool.plans", "mesh.seat.mesh-controller.tool.push", "mesh.seat.mesh-controller.tool.upgrade", "mesh.seat.mesh-delivery.tool.close", "mesh.seat.mesh-delivery.tool.groups", "mesh.seat.mesh-delivery.tool.release", "mesh.seat.mesh-delivery.tool.stalled", "mesh.seat.mesh-delivery.tool.stop", "mesh.seat.mesh-delivery.tool.times", "mesh.seat.node-backup.tool.backed-up.*", "mesh.seat.node-backup.tool.now.*", "mesh.seat.node-build-agent.accept.>", "mesh.seat.node-build-agent.check.>", "mesh.seat.node-build-agent.tool.>", "mesh.seat.node-intrusion-prevention.tool.banned.*", "mesh.seat.node-launcher.tool.secret.*", "mesh.seat.node-service-manager.tool.restart.*", "mesh.seat.operator-channel.tool.tell"] }
         subscribe: { allow: ["$JS.API.>", "$JS.EVENT.ADVISORY.CONSUMER.DELETED.>", "$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES.>", "$SRV.INFO", "$SRV.INFO.mesh-controller", "$SRV.INFO.mesh-controller.>", "$SRV.PING", "$SRV.PING.mesh-controller", "$SRV.PING.mesh-controller.>", "$SRV.STATS", "$SRV.STATS.mesh-controller", "$SRV.STATS.mesh-controller.>", "_DELIVER.controller", "_DELIVER.controller.>", "_INBOX.controller.>", "mesh.control.>", "mesh.mod.*.event.provisioner.failing", "mesh.mod.*.event.provisioner.recovered", "mesh.mod.*.event.provisioner.retirement", "mesh.mod.gitea.event.pull.merged", "mesh.mod.gitea.event.pull.updated", "mesh.mod.mesh-catalog.event.catching-up", "mesh.mod.mesh-catalog.event.upgraded", "mesh.seat.mesh-build-machine.event.built", "mesh.seat.mesh-controller.tool.>", "mesh.seat.node-build-agent.event.built", "mesh.seat.operator-channel.event.decided.mesh-controller"] }
         allow_responses: { max: 1, ttl: "1m" }
       } }

internal/broker/writers.go

@@ -236,6 +236,9 @@ var WritersTable = []WriterRow{
 	{State: "the predefined-keys mirror", Writer: "controller (lease holder), from its store, only on a change",
 		KeptIn: "key-value " + PredefinedBucket, Others: "read through `reads` as mesh-controller." + MirrorPredefined,
 		Subjects: kvOf(PredefinedBucket), Writes: isController},
+	{State: "the declared-packages mirror", Writer: "controller (lease holder), from the composition of each node, only on a change",
+		KeptIn: "key-value " + DeclaredPackagesBucket, Others: "read through `reads` as mesh-controller." + MirrorDeclaredPackages,
+		Subjects: kvOf(DeclaredPackagesBucket), Writes: isController},
 	// What a machine's provisioner client placed of a module's files (novox/hq ADR 0349 §4, design 57 P6): its own
 	// machine's word alone, which a walk's end and a gate wait for (ADR 0362, ADR 0349 §15). Kept newest per module
 	// in the stream ProvAppliedStream, and by the client in the provisioner server's `applied` bucket.

internal/broker/writers_test.go

@@ -49,6 +49,7 @@ var designRows = []string{
 	"a declaration's large files",
 	"the declared-config mirror",
 	"the predefined-keys mirror",
+	"the declared-packages mirror",
 	// The provisioner client's word on what it placed (novox/hq ADR 0349 §4, design 57 P6).
 	"a module's files placed on a machine",
 }

internal/inventory/declared_packages_test.go

@@ -0,0 +1,83 @@
+package inventory
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"slices"
+	"testing"
+)
+
+// aNodesPackages is the resources of a node whose modules declare packages: one package two modules declare present, one
+// declared absent, and a resource that is no package.
+func aNodesPackages() ([]map[string]any, map[string]string) {
+	return []map[string]any{
+			{"id": "web.pkg-curl", "type": "package", "package": "curl"},
+			{"id": "backup.pkg-curl", "type": "package", "package": "curl"},
+			{"id": "web.pkg-nano", "type": "package", "package": "nano", "absent": true},
+			{"id": "web.conf", "type": "file", "path": "/etc/web.conf"},
+		},
+		map[string]string{"web.pkg-curl": "web", "backup.pkg-curl": "backup", "web.pkg-nano": "web", "web.conf": "web"}
+}
+
+// 1840/AC5: the declared-packages mirror's value for a node names each package with the modules that declare it and whether
+// they declare it absent, and the same declaration is the same bytes however its resources are ordered, so a pass over an
+// unchanged node writes nothing.
+func TestTheDeclaredPackagesValueNamesEachPackageWithItsModules(t *testing.T) {
+	resources, owner := aNodesPackages()
+	got, err := DeclaredPackagesValue("one", resources, owner)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := `{"node":"one","packages":[{"package":"curl","modules":["backup","web"],"absent":false},` +
+		`{"package":"nano","modules":["web"],"absent":true}]}`
+	if string(got) != want {
+		t.Errorf("the value is\n%s\nwant\n%s", got, want)
+	}
+	reversed := slices.Clone(resources)
+	slices.Reverse(reversed)
+	again, err := DeclaredPackagesValue("one", reversed, owner)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, again) {
+		t.Errorf("the same declaration in another order is other bytes:\n%s\n%s", got, again)
+	}
+	if got := jsonFields(reflect.TypeOf(DeclaredPackagesMirrored{})); !slices.Equal(got, []string{"node", "packages"}) {
+		t.Errorf("the value carries %v", got)
+	}
+}
+
+// A node declaring no package has a value that says so, an empty list and not null.
+func TestANodeDeclaringNoPackageHasAnEmptyList(t *testing.T) {
+	got, err := DeclaredPackagesValue("one", nil, nil)
+	if err != nil || string(got) != `{"node":"one","packages":[]}` {
+		t.Errorf("the value is %s (%v)", got, err)
+	}
+}
+
+// 1840/S3: a node's value stays under the 64 KiB a mirror's key holds at far more packages than a node declares: 600
+// packages, each declared by four modules, is a few times what the largest node declares today.
+func TestTheDeclaredPackagesValueOfABigNodeFitsAKey(t *testing.T) {
+	var resources []map[string]any
+	owner := map[string]string{}
+	for p := 0; p < 600; p++ {
+		for m := 0; m < 4; m++ {
+			id := fmt.Sprintf("module-%d.pkg-%d", m, p)
+			resources = append(resources, map[string]any{"id": id, "type": "package", "package": fmt.Sprintf("package-%d", p)})
+			owner[id] = fmt.Sprintf("module-%d", m)
+		}
+	}
+	got, err := DeclaredPackagesValue("one", resources, owner)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var v DeclaredPackagesMirrored
+	if err := json.Unmarshal(got, &v); err != nil || len(v.Packages) != 600 {
+		t.Fatalf("the value holds %d packages (%v)", len(v.Packages), err)
+	}
+	if len(got) >= 64<<10 {
+		t.Errorf("the value is %d bytes, over the 64 KiB a key holds", len(got))
+	}
+}

internal/inventory/mirrors.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"sort"
 	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
@@ -191,3 +192,65 @@ func DeclaredOf(settings map[string]catalogue.SettingDeclaration) (map[string]De
 	}
 	return declaredMirrored(raw)
 }
+
+// PackageDeclared is one package a node's modules declare, as the declared-packages mirror holds it (ADR 0507 §5): its
+// name, the modules that declare it that way, sorted, and whether they declare it absent. A package some modules declare
+// present and others absent is two entries; the composition refuses that pair, so it is seen only while it is refused.
+type PackageDeclared struct {
+	Package string   `json:"package"`
+	Modules []string `json:"modules"`
+	Absent  bool     `json:"absent"`
+}
+
+// DeclaredPackagesMirrored is one node's value of the declared-packages mirror, keyed by the node: its packages sorted by
+// name (absent after present). Fixed fields and no time, so the same declaration is the same bytes (ADR 0289 §1).
+type DeclaredPackagesMirrored struct {
+	Node     string            `json:"node"`
+	Packages []PackageDeclared `json:"packages"`
+}
+
+// DeclaredPackagesValue is the mirror's value for one node, from the resources its composition declares and the module that
+// owns each (Composed.Owner, by resource id). A resource that is no package, or names none, is left out.
+func DeclaredPackagesValue(node string, resources []map[string]any, owner map[string]string) ([]byte, error) {
+	type key struct {
+		name   string
+		absent bool
+	}
+	by := map[key]map[string]bool{}
+	for _, r := range resources {
+		if fmt.Sprint(r["type"]) != "package" {
+			continue
+		}
+		name, _ := r["package"].(string)
+		if name == "" {
+			continue
+		}
+		k := key{name, r["absent"] == true}
+		if by[k] == nil {
+			by[k] = map[string]bool{}
+		}
+		if module := owner[fmt.Sprint(r["id"])]; module != "" {
+			by[k][module] = true
+		}
+	}
+	keys := make([]key, 0, len(by))
+	for k := range by {
+		keys = append(keys, k)
+	}
+	sort.Slice(keys, func(i, j int) bool {
+		if keys[i].name != keys[j].name {
+			return keys[i].name < keys[j].name
+		}
+		return !keys[i].absent && keys[j].absent
+	})
+	v := DeclaredPackagesMirrored{Node: node, Packages: []PackageDeclared{}}
+	for _, k := range keys {
+		modules := make([]string, 0, len(by[k]))
+		for m := range by[k] {
+			modules = append(modules, m)
+		}
+		sort.Strings(modules)
+		v.Packages = append(v.Packages, PackageDeclared{Package: k.name, Modules: modules, Absent: k.absent})
+	}
+	return json.Marshal(v)
+}

internal/recordmirror/mirror.go

@@ -57,10 +57,13 @@ var (
 	// mesh-config publishes as its own (design 57 K3).
 	Predefined = Mirror{Name: broker.MirrorPredefined, Bucket: broker.PredefinedBucket,
 		Event: link.KeyPredefinedChanged}
+	// DeclaredPackages is each node's packages its modules declare, keyed by the node (ADR 0507 §5). It raises no event:
+	// the seat's emits, which the SDK states, do not name one, and a reader reads the bucket when it is asked.
+	DeclaredPackages = Mirror{Name: broker.MirrorDeclaredPackages, Bucket: broker.DeclaredPackagesBucket}
 )
 
 // Mirrors is every mirror this package writes, in the order they are written.
-func Mirrors() []Mirror { return []Mirror{DeclaredConfig, Predefined} }
+func Mirrors() []Mirror { return []Mirror{DeclaredConfig, Predefined, DeclaredPackages} }
 
 // The changes an event says.
 const (
@@ -251,7 +254,7 @@ func (w *Writer) put(ctx context.Context, key string, value []byte, before kept,
 
 // say raises one write's event, tried once more when refused and then counted as lost.
 func (w *Writer) say(ctx context.Context, key, change string, fields []string, revision uint64) {
-	if w.Announce == nil {
+	if w.Announce == nil || w.Mirror.Event == "" {
 		return
 	}
 	e := Event{Mirror: w.Mirror.Name, Key: key, Change: change, Fields: fields, Revision: revision, At: w.now().UTC()}

internal/recordmirror/mirror_integration_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/nats-io/nats.go/jetstream"
 	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/inventory"
 	"github.com/novox/mesh-controller/internal/testbus"
 )
 
@@ -246,3 +247,49 @@ func TestNatsARemovalWithoutTheLeaseRemovesNothing(t *testing.T) {
 		t.Errorf("the key was removed without the lease: %v", err)
 	}
 }
+
+// 1840/AC5 (ADR 0507 §5, ADR 0289 §1): the declared-packages mirror, keyed by the node, writes a node's value once; a second
+// pass over the same declaration writes nothing (the bucket takes no message); a package newly declared changes the one key;
+// a node gone removes its key. It raises no event: the seat's emits name none for it.
+func TestNatsTheDeclaredPackagesMirrorWritesOnlyOnAChange(t *testing.T) {
+	js, api := aMirrorBus(t)
+	events := listen(t, js.Conn(), "mesh.seat."+broker.ControllerSeat+".event.>")
+	w := aWriter(t, js, api, DeclaredPackages)
+	ctx := t.Context()
+	value := func(node string, resources ...map[string]any) []byte {
+		t.Helper()
+		owner := map[string]string{}
+		for _, r := range resources {
+			owner[r["id"].(string)] = "web"
+		}
+		v, err := inventory.DeclaredPackagesValue(node, resources, owner)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return v
+	}
+	curl := map[string]any{"id": "web.curl", "type": "package", "package": "curl"}
+	nano := map[string]any{"id": "web.nano", "type": "package", "package": "nano", "absent": true}
+
+	if r, err := w.Sync(ctx, map[string][]byte{"one": value("one", curl), "two": value("two")}); err != nil ||
+		r != (Result{Written: 2}) {
+		t.Fatalf("the first pass wrote %+v (%v)", r, err)
+	}
+	before := writes(t, api, DeclaredPackages.Bucket)
+	if r, err := w.Sync(ctx, map[string][]byte{"one": value("one", curl), "two": value("two")}); err != nil || r != (Result{}) {
+		t.Errorf("a pass over the same declarations wrote %+v (%v)", r, err)
+	}
+	if got := writes(t, api, DeclaredPackages.Bucket) - before; got != 0 {
+		t.Errorf("a pass over the same declarations put %d messages in the bucket", got)
+	}
+	if r, err := w.Sync(ctx, map[string][]byte{"one": value("one", curl, nano), "two": value("two")}); err != nil ||
+		r != (Result{Written: 1}) {
+		t.Errorf("a package newly declared wrote %+v (%v)", r, err)
+	}
+	if r, err := w.Sync(ctx, map[string][]byte{"one": value("one", curl, nano)}); err != nil || r != (Result{Removed: 1}) {
+		t.Errorf("a node gone wrote %+v (%v)", r, err)
+	}
+	if said := settle(events, 1); len(said) != 0 {
+		t.Errorf("the declared-packages mirror raised %+v", said)
+	}
+}