Merge pull request 'Phase 5 (1/4): keep a facts snapshot for merge checks, and say when it goes stale (hq ADR 0237, S14)' (#95) from feat/facts-snapshot into main

cmd/mesh-controller/facts.go

@@ -0,0 +1,612 @@
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"slices"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/novox/mesh-host/validate"
+
+	"github.com/novox/mesh-controller/internal/artifacts"
+	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/catalogue"
+	snapshot "github.com/novox/mesh-controller/internal/facts"
+	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// The facts snapshot (novox/hq to-be 45 §9, ADR 0227 rule 9): what a merge check needs to judge a change
+// against the mesh that runs, written by the controller to the artifact store, where the build seat reads
+// it. internal/facts says what it holds and what it never holds; this composes it from the store and
+// keeps it current.
+
+// factsEvery is how often the snapshot is composed. It is kept when it moved — a machine, an
+// assignment, a seat, a setting, a build — or once a day when nothing did, so its age says the
+// controller is still writing it (S14).
+var factsEvery = 10 * time.Minute
+
+// factsDaily is how old a snapshot of an unchanged mesh may grow before it is written again.
+const factsDaily = 24 * time.Hour
+
+// factsStaleAfter is S14's bound: a snapshot older than this is one no check should be fed.
+const factsStaleAfter = 48 * time.Hour
+
+// factsExport is what this controller knows of the snapshot it keeps: when the newest was taken, its
+// content, and the last attempt's error.
+type factsExport struct {
+	mu      sync.Mutex
+	taken   time.Time
+	content string
+	digest  string
+	err     error
+	began   time.Time
+}
+
+// exportedFacts is this process's export, read by S14.
+var exportedFacts = &factsExport{}
+
+func (e *factsExport) last() (taken time.Time, digest string, began time.Time, err error) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	return e.taken, e.digest, e.began, e.err
+}
+
+func (e *factsExport) kept(f snapshot.Facts, content, digest string) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.taken, e.content, e.digest, e.err = f.Taken, content, digest, nil
+}
+
+func (e *factsExport) failed(err error) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.err = err
+}
+
+// exportingFacts keeps the snapshot current for as long as this controller holds the lease: ctx ends
+// when it stops acting.
+func exportingFacts(ctx context.Context, open *stores, busVersion func() string) {
+	exportedFacts.mu.Lock()
+	exportedFacts.began = time.Now()
+	exportedFacts.mu.Unlock()
+	// What the store holds already, so a restarted controller neither writes an unchanged snapshot again
+	// nor reads its age as zero.
+	if address, err := factsStore(ctx, open); err == nil {
+		if body, digest, err := (artifacts.Store{Address: address}).GetTagged(ctx, snapshot.Repository, snapshot.Tag); err == nil {
+			if f, err := snapshot.Decode(body); err == nil {
+				content, _ := f.Content()
+				exportedFacts.kept(f, content, digest)
+			}
+		}
+	}
+	failing := ""
+	first := time.NewTimer(time.Minute)
+	defer first.Stop()
+	tick := time.NewTicker(factsEvery)
+	defer tick.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-first.C:
+		case <-tick.C:
+		}
+		wrote, err := exportFacts(ctx, open, busVersion(), false)
+		why := ""
+		if err != nil {
+			why = err.Error()
+			exportedFacts.failed(err)
+		}
+		if why != failing {
+			if why != "" {
+				fmt.Printf("the facts snapshot cannot be kept: %s\n", why)
+			} else {
+				fmt.Println("the facts snapshot is kept again")
+			}
+			failing = why
+		}
+		if wrote != "" {
+			fmt.Printf("the facts snapshot moved and is kept as %s\n", short(strings.TrimPrefix(wrote, "sha256:")))
+		}
+	}
+}
+
+// exportFacts composes the snapshot and keeps it when it moved, or when the one kept is a day old, or
+// when told to. Answers the digest it kept, empty when it kept nothing.
+func exportFacts(ctx context.Context, open *stores, busVersion string, force bool) (string, error) {
+	f, err := gatherFacts(ctx, open, busVersion)
+	if err != nil {
+		return "", err
+	}
+	content, err := f.Content()
+	if err != nil {
+		return "", err
+	}
+	exportedFacts.mu.Lock()
+	unchanged := content == exportedFacts.content && time.Since(exportedFacts.taken) < factsDaily
+	exportedFacts.mu.Unlock()
+	if unchanged && !force {
+		return "", nil
+	}
+	body, err := f.Encode()
+	if err != nil {
+		return "", err
+	}
+	address, err := factsStore(ctx, open)
+	if err != nil {
+		return "", err
+	}
+	digest, err := (artifacts.Store{Address: address}).PutTagged(ctx, snapshot.Repository, snapshot.Tag, snapshot.MediaType, body)
+	if err != nil && digest == "" {
+		return "", err
+	}
+	exportedFacts.kept(f, content, digest)
+	return digest, err
+}
+
+// factsStore is the artifact store as this controller reaches it.
+func factsStore(ctx context.Context, open *stores) (string, error) {
+	shelf, err := open.inventory.Catalogue(ctx)
+	if err != nil {
+		return "", err
+	}
+	address, err := artifactStoreAddress(ctx, open.inventory, shelf, "")
+	if err != nil {
+		return "", err
+	}
+	if address == "" {
+		return "", errors.New("the artifact store is not on the private network, so there is nowhere to keep the facts")
+	}
+	return address, nil
+}
+
+// gatherFacts composes one snapshot from the store: read only, nothing made, nothing sent.
+func gatherFacts(ctx context.Context, open *stores, busVersion string) (snapshot.Facts, error) {
+	inv := open.inventory
+	f := snapshot.Facts{Format: snapshot.Format, Taken: time.Now().UTC(), Controller: snapshot.Build{Version: version}}
+	f.Versions.Bus = busVersion
+	storeVersion, err := inv.ServerVersion(ctx)
+	if err != nil {
+		return snapshot.Facts{}, fmt.Errorf("the store will not say its version: %w", err)
+	}
+	f.Versions.Store = storeVersion
+
+	nodes, err := inv.Nodes(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	overlays, err := inv.Overlays(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	place := map[string]inventory.Overlay{}
+	for _, o := range overlays {
+		place[o.Name] = o
+	}
+	entries, err := inv.Catalogued(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	shelf := map[string]catalogue.Manifest{}
+	for _, e := range entries {
+		shelf[e.Manifest.Module] = e.Manifest
+	}
+	current, err := inv.CurrentBuilds(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	read, err := inv.ReadRepositories(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	edges, err := inv.Dependencies(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+	holdings, err := inv.Holdings(ctx)
+	if err != nil {
+		return snapshot.Facts{}, err
+	}
+
+	// **Every name first**, so text read afterwards — a setting naming a machine, a problem naming a
+	// site — has it replaced wherever it appears.
+	scrub := snapshot.NewScrubber()
+	domains := map[string]string{}
+	for _, n := range nodes {
+		scrub.Machine(n.Name)
+		if n.Account != "" && n.Account != "root" {
+			scrub.Account(n.Account)
+		}
+		d, err := inv.PublicDomainOf(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		domains[n.Name] = scrub.Domain(d)
+	}
+	for _, o := range overlays {
+		scrub.Site(o.Site)
+	}
+
+	if c, ok := current["mesh-controller"]; ok {
+		f.Controller.Commit = c.Commit
+	}
+
+	gens, gensErr := generators(ctx, open)
+	hostShelf := shelf[hostModule]
+	meshWide := map[string]bool{}
+	engines := map[string]bool{}
+	for _, n := range nodes {
+		m := snapshot.Machine{Name: scrub.Machine(n.Name), Length: len(n.Name), Adopted: n.Adopted,
+			AccountHome: scrub.Text(n.AccountHome), NodeEngine: n.HostVersion, PublicDomain: domains[n.Name]}
+		switch n.Account {
+		case "", "root":
+			m.Account = n.Account
+		default:
+			m.Account = scrub.Account(n.Account)
+		}
+		if n.HostVersion != "" {
+			engines[n.HostVersion] = true
+		}
+		m.System = systemOf(hostShelf, n.HostVersion)
+		m.Libc = libcOf(m.System)
+		reported, err := inv.DescribedOf(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		m.Architecture, m.Kernel = reported.Architecture, reported.Kernel
+		capabilities, err := inv.Profile(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		for _, c := range capabilities {
+			kept := snapshot.Capability{Name: c.Name, Present: c.Present}
+			// The detail only where it is a version: everything else a detector says — a ruleset, a
+			// device, a path — is the machine's own business and no check reads it.
+			if c.Present && (c.Name == "container-runtime" || c.Name == "package-manager") {
+				kept.Detail = scrub.Text(c.Detail)
+			}
+			m.Capabilities = append(m.Capabilities, kept)
+		}
+		if o, ok := place[n.Name]; ok {
+			m.Site, m.Hub, m.Public, m.OnNetwork = scrub.Site(o.Site), o.Hub, o.Endpoint != "", o.Address != ""
+		}
+		assigned, err := inv.Assigned(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		m.Assigned = assigned
+		sent, known, err := inv.SentBuilds(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		if known && slices.Contains(assigned, broker.RuntimeModule) {
+			m.NodeTools = sent[broker.RuntimeModule]
+		}
+		pins, err := inv.PinsFor(ctx, n.Name)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		for provision, c := range pins {
+			m.Pins = append(m.Pins, snapshot.Pin{Provision: provision, Machine: scrub.Machine(c.Node), Module: c.Module})
+		}
+		for _, module := range assigned {
+			held, err := inv.SecretsOf(ctx, n.Name, module)
+			if err != nil {
+				return snapshot.Facts{}, err
+			}
+			for _, h := range held {
+				if h.Origin == inventory.OriginAccepted {
+					m.Accepted = append(m.Accepted, snapshot.Accepted{Module: module, Name: h.Name,
+						Provider: scrub.Machine(h.Provider), Local: h.Local})
+				}
+			}
+			layers, err := inv.SettingsFor(ctx, n.Name, module)
+			if err != nil {
+				return snapshot.Facts{}, err
+			}
+			for _, layer := range layers {
+				if layer.From == catalogue.MeshWideLayer {
+					if !meshWide[module] {
+						meshWide[module] = true
+						f.Settings = append(f.Settings, snapshot.Settings{Module: module, Values: scrub.Values(layer.Values)})
+					}
+					continue
+				}
+				m.Settings = append(m.Settings, snapshot.Settings{Module: module, Values: scrub.Values(layer.Values)})
+			}
+		}
+		m.Declaration = declarationFacts(ctx, open, n.Name, gens, gensErr, scrub)
+		if ctx.Err() != nil {
+			return snapshot.Facts{}, ctx.Err()
+		}
+		f.Machines = append(f.Machines, m)
+	}
+	for e := range engines {
+		f.Versions.NodeEngines = append(f.Versions.NodeEngines, e)
+	}
+
+	// Seats and their holders, and from them the roles a machine is named by.
+	roles := map[string][]string{}
+	seats := map[string]*snapshot.Seat{}
+	for _, h := range holdings {
+		key := h.Claim + "\x00" + h.Scope
+		s, ok := seats[key]
+		if !ok {
+			s = &snapshot.Seat{Name: h.Claim, Scope: h.Scope}
+			seats[key] = s
+		}
+		s.Holders = append(s.Holders, snapshot.Holder{Machine: scrub.Machine(h.Node), Module: h.Module})
+		if h.Scope == catalogue.ScopeMesh {
+			role := "holds " + h.Claim
+			if h.Claim == catalogue.ControllerSeatName {
+				role = "the control node"
+			}
+			roles[h.Node] = append(roles[h.Node], role)
+		}
+	}
+	for _, s := range seats {
+		f.Seats = append(f.Seats, *s)
+	}
+	for i := range f.Machines {
+		for _, n := range nodes {
+			if scrub.Machine(n.Name) != f.Machines[i].Name {
+				continue
+			}
+			f.Machines[i].Roles = roles[n.Name]
+			if f.Machines[i].Hub {
+				f.Machines[i].Roles = append(f.Machines[i].Roles, "the hub")
+			}
+		}
+	}
+
+	// Every module, as the mesh holds it, and where it is built from.
+	newest := map[string]inventory.Source{}
+	count := map[string]int{}
+	for _, e := range entries {
+		raw, err := json.Marshal(e.Manifest)
+		if err != nil {
+			return snapshot.Facts{}, err
+		}
+		mod := snapshot.Module{Name: e.Manifest.Module, Repository: e.Source.Repository, Path: e.Source.Path,
+			Commit: e.Source.BuiltFrom, Provided: e.Provided, RollOut: current[e.Manifest.Module].RollOut,
+			Manifest: raw}
+		for _, r := range read[e.Manifest.Module] {
+			mod.Reads = append(mod.Reads, r.Repository)
+		}
+		f.Modules = append(f.Modules, mod)
+		if e.Provided || e.Source.Repository == "" {
+			continue
+		}
+		count[e.Source.Repository]++
+		if was, ok := newest[e.Source.Repository]; !ok || e.Source.Seen.After(was.Seen) {
+			newest[e.Source.Repository] = e.Source
+		}
+	}
+	for repository, s := range newest {
+		commit := s.Head
+		if commit == "" {
+			commit = s.BuiltFrom
+		}
+		f.Sources = append(f.Sources, snapshot.Source{Repository: repository, Commit: commit, Modules: count[repository]})
+	}
+	for _, e := range edges {
+		f.Edges = append(f.Edges, snapshot.Edge{From: e.From, To: e.To, Kind: e.Kind})
+	}
+	f.Sorted()
+	return f, nil
+}
+
+// declarationFacts is how one machine's declaration composes now, as the next push would compose it and
+// without making anything (D1's composition), and whether the node-engine's validator takes it.
+func declarationFacts(ctx context.Context, open *stores, node string, gens map[string]catalogue.Generator,
+	gensErr error, scrub *snapshot.Scrubber) snapshot.Declaration {
+	var d snapshot.Declaration
+	if gensErr != nil {
+		d.Problems = []string{scrub.Text("the private network cannot be computed: " + oneLine(gensErr.Error()))}
+		return d
+	}
+	declared, problems, err := composedAndValidated(ctx, open, node, gens, Foreseeing)
+	if err != nil {
+		d.Problems = []string{scrub.Text(oneLine(err.Error()))}
+		return d
+	}
+	for _, p := range problems {
+		d.Problems = append(d.Problems, scrub.Text(p))
+	}
+	d.Composes = len(problems) == 0
+	if body, err := declared.Body(); err == nil {
+		d.Digest = fmt.Sprintf("sha256:%x", sha256.Sum256(body))
+	}
+	d.Resources = resourceNames(declared.Resources)
+	for module, why := range declared.leftOutWhy {
+		if d.LeftOut == nil {
+			d.LeftOut = map[string]string{}
+		}
+		d.LeftOut[module] = scrub.Text(why)
+	}
+	for _, o := range declared.withheld {
+		d.Withheld = append(d.Withheld, scrub.Text(o.String()))
+	}
+	for _, u := range declared.unbound {
+		d.Unbound = append(d.Unbound, scrub.Text(u.String()))
+	}
+	sort.Strings(d.Withheld)
+	sort.Strings(d.Unbound)
+	return d
+}
+
+// composedAndValidated composes one machine's declaration — as a push would (Allocating) or as the next
+// push will without making anything (Foreseeing) — with the order it was last sent, and runs the
+// node-engine's own validator over the body. An error is that it did not compose; problems are what the
+// validator refuses.
+func composedAndValidated(ctx context.Context, open *stores, node string, gens map[string]catalogue.Generator,
+	choosing Choosing) (sendable, []string, error) {
+	plan, settings, err := planFor(ctx, open, node)
+	if err != nil {
+		return sendable{}, nil, err
+	}
+	declared, err := declarationWith(ctx, open, node, plan, settings, gens, choosing)
+	if err != nil {
+		return sendable{}, nil, err
+	}
+	record, err := open.inventory.NodeByName(ctx, node)
+	if err != nil {
+		return sendable{}, nil, err
+	}
+	if declared.Sequence, err = open.inventory.Sequence(ctx, record.ID); err != nil {
+		return sendable{}, nil, err
+	}
+	if declared.Epoch, err = open.inventory.SentEpoch(ctx, record.ID); err != nil {
+		return sendable{}, nil, err
+	}
+	body, err := declared.Body()
+	if err != nil {
+		return sendable{}, nil, err
+	}
+	return declared, validate.Declaration(body), nil
+}
+
+// resourceNames are a declaration's resources as `type:id`, sorted.
+func resourceNames(resources []map[string]any) []string {
+	out := make([]string, 0, len(resources))
+	for _, r := range resources {
+		kind, _ := r["type"].(string)
+		id, _ := r["id"].(string)
+		out = append(out, kind+":"+id)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// systemOf is the system a node-engine of that version was built for, read from the build the mesh
+// holds: the artifact a resource delivered into `versions/<version>` came from is named for its system
+// (`host-arch`). Empty when the version is not a delivered one — an engine placed by hand.
+func systemOf(host catalogue.Manifest, version string) string {
+	if version == "" {
+		return ""
+	}
+	for _, r := range host.Resources {
+		path, _ := r["path"].(string)
+		if !strings.HasSuffix(path, "/versions/"+version) {
+			continue
+		}
+		source, _ := r["source"].(string)
+		for _, part := range strings.Split(source, "/") {
+			if system, ok := strings.CutPrefix(part, "host-"); ok && system != "" {
+				return system
+			}
+		}
+	}
+	return ""
+}
+
+// libcOf is the C library of a system the node-engine is built for.
+func libcOf(system string) string {
+	switch system {
+	case "arch":
+		return "glibc"
+	case "alpine":
+		return "musl"
+	case "android":
+		return "bionic"
+	}
+	return ""
+}
+
+// factsCommand is `facts`: what the controller keeps, and keeping it now.
+//
+//	facts                 the snapshot the artifact store holds: when, which, how many machines
+//	facts show            the same, whole, as JSON
+//	facts export          compose and keep one now
+//	facts compose         compose one and print it, keeping nothing
+func factsCommand(ctx context.Context, args []string) error {
+	set := flag.NewFlagSet("facts", flag.ContinueOnError)
+	rest, err := parseAround(set, args)
+	if err != nil {
+		return err
+	}
+	what := ""
+	if len(rest) > 0 {
+		what = rest[0]
+	}
+	open, err := openStores(ctx)
+	if err != nil {
+		return err
+	}
+	defer open.Close()
+	switch what {
+	case "", "show":
+		address, err := factsStore(ctx, open)
+		if err != nil {
+			return err
+		}
+		body, digest, err := (artifacts.Store{Address: address}).GetTagged(ctx, snapshot.Repository, snapshot.Tag)
+		if err != nil {
+			return err
+		}
+		if what == "show" {
+			_, err := os.Stdout.Write(body)
+			return err
+		}
+		f, err := snapshot.Decode(body)
+		if err != nil {
+			return err
+		}
+		fmt.Printf("the facts snapshot kept as %s:%s is %s, taken %s (%s ago) by controller %s\n",
+			snapshot.Repository, snapshot.Tag, short(strings.TrimPrefix(digest, "sha256:")),
+			f.Taken.Format(time.RFC3339), ago(time.Since(f.Taken)), orNone(f.Controller.Commit))
+		fmt.Printf("  %d machine(s), %d module(s), %d seat(s); the longest machine name is %d characters\n",
+			len(f.Machines), len(f.Modules), len(f.Seats), f.Longest())
+		fmt.Printf("  the bus runs %s, the store %s\n", orNone(f.Versions.Bus), orNone(f.Versions.Store))
+		for _, m := range f.Machines {
+			state := "composes"
+			if !m.Declaration.Composes {
+				state = "does NOT compose: " + strings.Join(m.Declaration.Problems, "; ")
+			}
+			fmt.Printf("  %-12s %s; %d module(s); %s\n", m.Name, m.Described(), len(m.Assigned), state)
+		}
+		return nil
+	case "export", "compose":
+		busVersion := ""
+		if server, err := connectLink(ctx, nil, nil, nil); err == nil {
+			busVersion = busVersionOf(server)
+			server.Close()
+		}
+		if what == "compose" {
+			f, err := gatherFacts(ctx, open, busVersion)
+			if err != nil {
+				return err
+			}
+			body, err := f.Encode()
+			if err != nil {
+				return err
+			}
+			_, err = os.Stdout.Write(append(body, '\n'))
+			return err
+		}
+		digest, err := exportFacts(ctx, open, busVersion, true)
+		if err != nil {
+			return err
+		}
+		fmt.Printf("the facts snapshot is kept as %s:%s, %s\n", snapshot.Repository, snapshot.Tag, digest)
+		return nil
+	}
+	return fmt.Errorf("facts [show|export|compose], not %q", what)
+}
+
+// busVersionOf is the bus server's release, as it told this connection.
+func busVersionOf(server *link.Server) string {
+	if bus, ok := server.Bus().(link.OverNATS); ok && bus.Conn != nil {
+		return bus.Conn.ConnectedServerVersion()
+	}
+	return ""
+}

cmd/mesh-controller/facts_test.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	snapshot "github.com/novox/mesh-controller/internal/facts"
+)
+
+// The facts snapshot (novox/hq to-be 45 §9): composed from the store, every machine under a pseudonym
+// of its name's length, and nothing of the installation in it — no secret, no address, no name.
+
+// aMeshWithSecrets is aMesh with a provider and its consumers, a value given by hand, settings carrying
+// a password, an address and a machine's name, and a push's worth of credentials made.
+func aMeshWithSecrets(t *testing.T) (*stores, []string) {
+	t.Helper()
+	open := aMesh(t)
+	ctx := t.Context()
+	register(t, open, catalogue.Manifest{Module: "objects", Version: "1",
+		Provides: []catalogue.Offer{{Name: "s3-bucket", Scope: catalogue.ScopeMesh,
+			Identity: &catalogue.OfferIdentity{Max: 20, In: "an S3 access key"}}},
+		Receives: map[string]string{"s3-bucket": "/var/lib/mesh/objects/mesh.json"}})
+	register(t, open, catalogue.Manifest{Module: "files", Version: "1", Requires: []string{"s3-bucket"},
+		Resources: []map[string]any{{"id": "config", "type": "file", "path": "/etc/files/config.json",
+			"mode": "0600", "content": "{}", "merge": "json"}}})
+	for _, a := range [][2]string{{"anchor", "objects"}, {"laptop", "files"}} {
+		if _, err := assign(ctx, open, a[0], a[1]); err != nil {
+			t.Fatalf("assign %s %s: %v", a[0], a[1], err)
+		}
+	}
+	secrets := []string{"Hunter2-Is-Not-A-Password-9f8e7d", "0123456789abcdefABCDEF0123456789zz"}
+	if err := open.inventory.SetSettings(ctx, "", "files", map[string]any{
+		"admin_password": secrets[0], "upstream": "10.77.0.9", "hub": "anchor"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := open.inventory.SetSettings(ctx, "laptop", "files", map[string]any{
+		"note": "reach me at 192.168.1.135, token " + secrets[1]}); err != nil {
+		t.Fatal(err)
+	}
+	// A push's worth of composition, which makes the pair credential the consumer is sent.
+	gens, err := generators(ctx, open)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, node := range []string{"laptop", "anchor"} {
+		if _, _, err := composedAndValidated(ctx, open, node, gens, Allocating); err != nil {
+			t.Fatalf("%s does not compose: %v", node, err)
+		}
+	}
+	issued, err := open.inventory.SecretsFrom(ctx, "anchor")
+	if err != nil || len(issued) == 0 {
+		t.Fatalf("no credential was made for the consumer: %v", err)
+	}
+	for _, s := range issued {
+		// Sealed, never kept plain (ADR 0004): the sealed blobs are what the store holds, and none may leave.
+		secrets = append(secrets, s.ForConsumer, s.ForProvider)
+	}
+	return open, secrets
+}
+
+func TestTheFactsCarryNoSecretNoAddressAndNoName(t *testing.T) {
+	open, secrets := aMeshWithSecrets(t)
+	f, err := gatherFacts(t.Context(), open, "2.11.17")
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, err := f.Encode()
+	if err != nil {
+		t.Fatal(err)
+	}
+	text := string(body)
+	for _, s := range secrets {
+		if s != "" && strings.Contains(text, s) {
+			t.Errorf("a secret is in the snapshot: %q", s)
+		}
+	}
+	for _, leaked := range []string{"anchor", "laptop", "10.77.0.", "192.168.1.135", ".example:51820"} {
+		if strings.Contains(text, leaked) {
+			t.Errorf("%q is in the snapshot", leaked)
+		}
+	}
+	// Every address it carries is a documentation address.
+	for _, a := range regexp.MustCompile(`\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b`).FindAllString(text, -1) {
+		if !strings.HasPrefix(a, "192.0.2.") && !strings.HasPrefix(a, "198.51.100.") && !strings.HasPrefix(a, "203.0.113.") {
+			t.Errorf("%s is an address outside the documentation ranges", a)
+		}
+	}
+
+	// What a check needs is there: every machine, its length, its modules, its declaration composing.
+	if len(f.Machines) != 2 || f.Longest() != len("laptop") {
+		t.Fatalf("machines %+v, longest %d", f.Machines, f.Longest())
+	}
+	anchor := snapshot.Pseudonym("machine", "anchor")
+	m, ok := f.Machine(anchor)
+	if !ok || !m.Hub || !strings.Contains(m.Described(), "the hub") || len(m.Name) != len("anchor") {
+		t.Fatalf("the anchor reads as %+v", m)
+	}
+	if !m.Declaration.Composes || m.Declaration.Digest == "" || len(m.Declaration.Resources) == 0 {
+		t.Errorf("the anchor's declaration reads as %+v", m.Declaration)
+	}
+	laptop, _ := f.Machine(snapshot.Pseudonym("machine", "laptop"))
+	if strings.Join(laptop.Assigned, ",") != "files,mesh-wireguard" && !strings.Contains(strings.Join(laptop.Assigned, ","), "files") {
+		t.Errorf("the laptop's assignments read as %v", laptop.Assigned)
+	}
+	var meshWide map[string]any
+	for _, s := range f.Settings {
+		if s.Module == "files" {
+			meshWide = s.Values
+		}
+	}
+	if meshWide["admin_password"] != snapshot.Withheld || meshWide["hub"] != anchor {
+		t.Errorf("the mesh-wide settings read as %v", meshWide)
+	}
+	if f.Versions.Bus != "2.11.17" || f.Versions.Store == "" {
+		t.Errorf("versions read as %+v", f.Versions)
+	}
+	var objects bool
+	for _, mod := range f.Modules {
+		objects = objects || mod.Name == "objects" && len(mod.Manifest) > 0
+	}
+	if !objects {
+		t.Error("the modules the mesh holds are not in the snapshot")
+	}
+
+	// And an unchanged mesh is the same content a moment later.
+	again, err := gatherFacts(t.Context(), open, "2.11.17")
+	if err != nil {
+		t.Fatal(err)
+	}
+	a, _ := f.Content()
+	b, _ := again.Content()
+	if a != b {
+		t.Error("two snapshots of an unchanged mesh differ, so it would be written again every ten minutes")
+	}
+}

cmd/mesh-controller/main.go

@@ -114,6 +114,9 @@ func run() error {
 		return brokerCommand(ctx, args[1:])
 	case "serve":
 		return serve(ctx)
+	// The facts snapshot a merge check is fed (novox/hq to-be 45 §9).
+	case "facts":
+		return factsCommand(ctx, args[1:])
 	case "upgrade":
 		return upgradeCommand(ctx, args[1:])
 	// The bus as a planned step (novox/hq to-be 45 §8, ADR 0236).

cmd/mesh-controller/push.go

@@ -212,6 +212,9 @@ func serve(ctx context.Context) (err error) {
 	givenEvents = bus
 	// Composed now and kept current, before the verb that answers from it is served.
 	go statusFrom.keep(ctx)
+	// The facts snapshot a merge check is fed (novox/hq to-be 45 §9): kept current while this
+	// controller holds the lease, read by the build seat from the artifact store.
+	go exportingFacts(ctx, open, bus.Conn.ConnectedServerVersion)
 	// Every call carries the lease's epoch, and its record is written only under the lease (novox/hq
 	// to-be 45 §6).
 	link.Calls.UnderLease(func() (uint64, error) { return theLease.epoch(ctx) })

cmd/mesh-controller/signals.go

@@ -183,9 +183,11 @@ var signalsTable = []signalRow{
 		newest: func(f *signalFacts) time.Time {
 			return newestOf(f.staleRefusals, func(w link.WriterRefusals) time.Time { return w.Last })
 		}},
-	{Row: "S14", Signal: "facts snapshot exported", Emitter: "controller", Trigger: "daily",
+	{Row: "S14", Signal: "facts snapshot exported", Emitter: "controller", Trigger: "when it moved, and daily",
-		Bound: "2 days", Kind: "facts-stale", Severity: conditions.Warning, Phase: 5,
+		Bound: "2 days: a snapshot older than that, or none kept since this controller began two days ago",
-		Deferred: "the facts snapshot is built in Phase 5 (to-be 45 §9): nothing exports one yet"},
+		Kind:  "facts-stale", Severity: conditions.Warning, Phase: 5,
+		needs: func(*signalFacts) error { return nil }, watch: watchFacts,
+		newest: func(f *signalFacts) time.Time { return f.facts.taken }},
 	{Row: "S15", Signal: "a hand act with a cause already recorded", Emitter: "hand-act log",
 		Trigger: "each act", Bound: "the second within 14 days; clears when fewer than two remain within 14 days",
 		Kind: "healer-wanted", Severity: conditions.Warning, Phase: 3,
@@ -195,6 +197,31 @@ var signalsTable = []signalRow{
 		}},
 }
 
+// watchFacts is S14: the snapshot a merge check is fed is older than its bound, or none was kept since
+// this controller began that long ago (novox/hq to-be 45 §9). A check fed a stale snapshot judges a change
+// against a mesh that no longer is, which is the fault the snapshot exists to end.
+func watchFacts(f *signalFacts) []conditions.Observation {
+	since := f.facts.taken
+	if since.IsZero() {
+		since = f.facts.began
+	}
+	if since.IsZero() || f.now.Sub(since) <= factsStaleAfter {
+		return nil
+	}
+	said := "none kept since this controller began " + ago(f.now.Sub(since)) + " ago"
+	if !f.facts.taken.IsZero() {
+		said = "the newest kept was taken " + ago(f.now.Sub(f.facts.taken)) + " ago"
+	}
+	if f.facts.err != nil {
+		said += "; the last attempt: " + oneLine(f.facts.err.Error())
+	}
+	return []conditions.Observation{{Scope: conditions.ScopeCore, ID: "facts", Kind: "facts-stale", Token: "stale",
+		Severity: conditions.Warning,
+		Summary: fmt.Sprintf("the facts snapshot merge checks are fed is stale (bound %s): a change is judged against a "+
+			"mesh that no longer is", ago(factsStaleAfter)),
+		Said: said}}
+}
+
 // newestOf is the newest time among things.
 func newestOf[T any](list []T, at func(T) time.Time) time.Time {
 	var newest time.Time

cmd/mesh-controller/signals_test.go

@@ -37,6 +37,7 @@ func calm(now time.Time) *signalFacts {
 		selfCheck:     selfCheckFacts{last: now.Add(-time.Minute), every: 5 * time.Minute},
 		lostConsumers: map[string]bool{}, epochs: map[int64]inventory.Epoch{},
 		lease: leaseFacts{held: true, epoch: 57, renewed: now.Add(-2 * time.Second)},
+		facts: factsFacts{taken: now.Add(-time.Hour), began: now.Add(-time.Hour)},
 	}
 }
 
@@ -125,6 +126,11 @@ var suppressions = map[string]suppression{
 		inside: func(f *signalFacts) { f.staleRefusals = refusedBy(f.now, 41, 5) },
 		past:   func(f *signalFacts) { f.staleRefusals = refusedBy(f.now, 41, 6) },
 	},
+	// The snapshot a merge check is fed, older than two days; or none kept by a controller two days up.
+	"S14": {
+		inside: func(f *signalFacts) { f.facts.taken = f.now.Add(-47 * time.Hour) },
+		past:   func(f *signalFacts) { f.facts.taken = f.now.Add(-49 * time.Hour) },
+	},
 	// Twice by hand within a fortnight is a healer wanted; once, or the first of two a day too old, is not.
 	"S15": {
 		inside: func(f *signalFacts) {

cmd/mesh-controller/watchdogs.go

@@ -89,6 +89,16 @@ type signalFacts struct {
 	// lease is this controller's standing to the lease, and the epochs that ended lately (S12).
 	lease    leaseFacts
 	leaseErr error
+
+	// facts is the snapshot this controller keeps for merge checks (S14).
+	facts factsFacts
+}
+
+// factsFacts is when the newest facts snapshot was taken, when this controller began keeping it, and
+// the last attempt's error.
+type factsFacts struct {
+	taken, began time.Time
+	err          error
 }
 
 type leaseFacts struct {
@@ -313,6 +323,7 @@ func (w *watchdogs) gather(ctx context.Context) *signalFacts {
 	f.advisories = link.Advisories.Since(now.Add(-advisoryQuiet))
 	f.lostConsumers, f.advisoriesErr = w.lostConsumers(ctx, f.advisories)
 	f.handActs, f.handActsErr = w.gatherHandActs(ctx, now)
+	f.facts.taken, _, f.facts.began, f.facts.err = exportedFacts.last()
 	return f
 }
 

internal/artifacts/tagged.go

@@ -0,0 +1,179 @@
+package artifacts
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+)
+
+// A document the mesh keeps under a name, read by whoever asks for that name (novox/hq to-be 45 §9).
+//
+// **The one thing the mesh names by tag.** Everything a machine runs is pinned by digest (ADR 0189), and
+// holders are put untagged so the collector's own rule keeps them. The facts snapshot is the opposite
+// case: what a reader wants is *the newest*, never a particular one, and a tag is the store's own word
+// for that. So it is put as the smallest OCI manifest naming one layer, under a tag; putting the next
+// moves the tag, and **the manifest it replaced is deleted by its digest**: the store's nightly collector
+// keeps every manifest, tagged or not, and marks what each names — so a replaced snapshot left in place
+// would be kept for ever, one more every day. Deleted, its layer is named by nothing and the next
+// collection takes it: the store keeps the newest, and nothing grows.
+
+// MaxTagged is the largest document put or read this way: a snapshot of a large mesh is a few
+// megabytes, and a reader is never made to swallow an answer of any size.
+const MaxTagged = 64 << 20
+
+// ErrNoTag is the answer when the store holds nothing under the tag: never put, or collected.
+var ErrNoTag = errors.New("the artifact store holds nothing under that name")
+
+// PutTagged puts body as the only layer of a manifest in repository and points tag at it. Answers the
+// layer's digest — what a reader quotes as "the snapshot I read".
+func (s Store) PutTagged(ctx context.Context, repository, tag, mediaType string, body []byte) (string, error) {
+	if s.Address == "" {
+		return "", fmt.Errorf("this mesh has no artifact store on its network to keep %s:%s in", repository, tag)
+	}
+	if len(body) > MaxTagged {
+		return "", fmt.Errorf("%s:%s is %d bytes, over the %d the store is given", repository, tag, len(body), MaxTagged)
+	}
+	sum := sha256.Sum256(body)
+	digest := "sha256:" + hex.EncodeToString(sum[:])
+	// What the tag names now, so it can be let go of once the new one stands. Asked before the put:
+	// after it, the tag names the new one.
+	replaced, err := s.manifestDigest(ctx, repository, tag)
+	if err != nil {
+		return "", err
+	}
+	if err := s.putBlob(ctx, repository, digest, body); err != nil {
+		return "", err
+	}
+	if err := s.putBlob(ctx, repository, emptyDigest, emptyConfig); err != nil {
+		return "", err
+	}
+	manifest, err := json.Marshal(holderManifest{
+		SchemaVersion: 2,
+		MediaType:     mediaManifest,
+		Config:        descriptor{MediaType: mediaEmpty, Digest: emptyDigest, Size: int64(len(emptyConfig))},
+		Layers:        []descriptor{{MediaType: mediaType, Digest: digest, Size: int64(len(body))}},
+	})
+	if err != nil {
+		return "", err
+	}
+	request, err := http.NewRequestWithContext(ctx, http.MethodPut, s.url(repository, "manifests", tag),
+		bytes.NewReader(manifest))
+	if err != nil {
+		return "", err
+	}
+	request.Header.Set("Content-Type", mediaManifest)
+	response, err := s.client().Do(request)
+	if err != nil {
+		return "", fmt.Errorf("cannot reach the artifact store at %s: %w", s.Address, err)
+	}
+	defer response.Body.Close()
+	if response.StatusCode != http.StatusCreated {
+		said, _ := io.ReadAll(io.LimitReader(response.Body, 4096))
+		return "", fmt.Errorf("the artifact store refused %s:%s: %s %s", repository, tag, response.Status,
+			strings.TrimSpace(string(said)))
+	}
+	mSum := sha256.Sum256(manifest)
+	if put := "sha256:" + hex.EncodeToString(mSum[:]); replaced != "" && replaced != put {
+		// The new one stands; the old one is let go of. A refusal here leaves one more snapshot in the
+		// store, which is said and is not a failure of the put: the tag already names the new one.
+		if err := s.remove(ctx, s.url(repository, "manifests", replaced), repository+"/manifests/"+replaced); err != nil &&
+			err != Gone {
+			return digest, fmt.Errorf("%s:%s now names the new document, and the one it replaced could not be "+
+				"let go of: %w", repository, tag, err)
+		}
+	}
+	return digest, nil
+}
+
+// manifestDigest is the digest of the manifest tag names in repository; empty when it names none.
+func (s Store) manifestDigest(ctx context.Context, repository, tag string) (string, error) {
+	request, err := http.NewRequestWithContext(ctx, http.MethodHead, s.url(repository, "manifests", tag), nil)
+	if err != nil {
+		return "", err
+	}
+	for _, media := range manifestAccept {
+		request.Header.Add("Accept", media)
+	}
+	response, err := s.client().Do(request)
+	if err != nil {
+		return "", fmt.Errorf("cannot reach the artifact store at %s: %w", s.Address, err)
+	}
+	defer response.Body.Close()
+	switch response.StatusCode {
+	case http.StatusOK:
+		return response.Header.Get("Docker-Content-Digest"), nil
+	case http.StatusNotFound:
+		return "", nil
+	default:
+		return "", fmt.Errorf("the artifact store answered %s for %s:%s", response.Status, repository, tag)
+	}
+}
+
+// GetTagged reads the one layer of the manifest tag names in repository, and its digest. ErrNoTag when
+// the store holds nothing under it.
+func (s Store) GetTagged(ctx context.Context, repository, tag string) ([]byte, string, error) {
+	if s.Address == "" {
+		return nil, "", fmt.Errorf("this mesh has no artifact store on its network to read %s:%s from", repository, tag)
+	}
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, s.url(repository, "manifests", tag), nil)
+	if err != nil {
+		return nil, "", err
+	}
+	for _, media := range manifestAccept {
+		request.Header.Add("Accept", media)
+	}
+	response, err := s.client().Do(request)
+	if err != nil {
+		return nil, "", fmt.Errorf("cannot reach the artifact store at %s: %w", s.Address, err)
+	}
+	defer response.Body.Close()
+	switch response.StatusCode {
+	case http.StatusOK:
+	case http.StatusNotFound:
+		return nil, "", fmt.Errorf("%w: %s:%s", ErrNoTag, repository, tag)
+	default:
+		return nil, "", fmt.Errorf("the artifact store answered %s for %s:%s", response.Status, repository, tag)
+	}
+	var m holderManifest
+	if err := json.NewDecoder(io.LimitReader(response.Body, 1<<20)).Decode(&m); err != nil {
+		return nil, "", fmt.Errorf("%s:%s is not a manifest the mesh wrote: %w", repository, tag, err)
+	}
+	if len(m.Layers) != 1 {
+		return nil, "", fmt.Errorf("%s:%s names %d layers; the mesh writes one", repository, tag, len(m.Layers))
+	}
+	layer := m.Layers[0]
+	if layer.Size > MaxTagged {
+		return nil, "", fmt.Errorf("%s:%s is %d bytes, over the %d a reader takes", repository, tag, layer.Size, MaxTagged)
+	}
+	blob, err := http.NewRequestWithContext(ctx, http.MethodGet, s.url(repository, "blobs", layer.Digest), nil)
+	if err != nil {
+		return nil, "", err
+	}
+	got, err := s.client().Do(blob)
+	if err != nil {
+		return nil, "", fmt.Errorf("cannot reach the artifact store at %s: %w", s.Address, err)
+	}
+	defer got.Body.Close()
+	if got.StatusCode != http.StatusOK {
+		return nil, "", fmt.Errorf("the artifact store names %s for %s:%s and answered %s for it",
+			layer.Digest, repository, tag, got.Status)
+	}
+	body, err := io.ReadAll(io.LimitReader(got.Body, MaxTagged+1))
+	if err != nil {
+		return nil, "", err
+	}
+	// **Read back against its own digest**: a reader is told which snapshot it read, and a truncated or
+	// substituted body must not pass as that one.
+	sum := sha256.Sum256(body)
+	if "sha256:"+hex.EncodeToString(sum[:]) != layer.Digest {
+		return nil, "", fmt.Errorf("%s:%s read back as something other than %s", repository, tag, layer.Digest)
+	}
+	return body, layer.Digest, nil
+}

internal/artifacts/tagged_test.go

@@ -0,0 +1,88 @@
+package artifacts
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+	"time"
+)
+
+// The facts snapshot is put under a tag and read back by it (novox/hq to-be 45 §9).
+//
+// Against the very registry the mesh's store runs, because what is asserted is the registry's answer:
+// that a manifest put by tag is read by tag, that the layer comes back whole and checked, and that the
+// snapshot a newer one replaced is the collector's to take while the newest is kept. Raised as the
+// collector test above says, with MESH_TEST_REGISTRY and MESH_TEST_REGISTRY_CONTAINER.
+func TestLiveADocumentPutUnderATagIsReadBackAndOnlyTheNewestIsKept(t *testing.T) {
+	address := os.Getenv("MESH_TEST_REGISTRY")
+	container := os.Getenv("MESH_TEST_REGISTRY_CONTAINER")
+	if address == "" || container == "" {
+		t.Skip("no MESH_TEST_REGISTRY / MESH_TEST_REGISTRY_CONTAINER; see the collector test's comment for the registry to raise")
+	}
+	ctx := context.Background()
+	store := Store{Address: address}
+	repository := fmt.Sprintf("facts-live-%d", time.Now().UnixNano())
+
+	if _, _, err := store.GetTagged(ctx, repository, "latest"); !errors.Is(err, ErrNoTag) {
+		t.Fatalf("nothing was put and the read said %v, not that nothing is there", err)
+	}
+	first := []byte(`{"facts":1,"taken":"first"}`)
+	firstDigest, err := store.PutTagged(ctx, repository, "latest", "application/vnd.novox.mesh.facts.v1+json", first)
+	if err != nil {
+		t.Fatal(err)
+	}
+	second := []byte(`{"facts":1,"taken":"second"}`)
+	secondDigest, err := store.PutTagged(ctx, repository, "latest", "application/vnd.novox.mesh.facts.v1+json", second)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, digest, err := store.GetTagged(ctx, repository, "latest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != string(second) || digest != secondDigest {
+		t.Fatalf("read back %q (%s), not the newest put %q (%s)", got, digest, second, secondDigest)
+	}
+
+	// The collector, as the store's nightly step runs it — with no `--delete-untagged`: the newest kept,
+	// the replaced one taken because its manifest was let go of.
+	out, err := exec.Command("docker", "exec", container, "registry", "garbage-collect",
+		"/etc/docker/registry/config.yml").CombinedOutput()
+	if err != nil {
+		t.Fatalf("the collector did not run: %v\n%s", err, out)
+	}
+	if got, _, err := store.GetTagged(ctx, repository, "latest"); err != nil || string(got) != string(second) {
+		t.Fatalf("after collection the newest reads %q, %v", got, err)
+	}
+	// On the store's disk, not as the running server answers: it caches blob descriptors in memory.
+	onDisk := func(digest string) bool {
+		hex := strings.TrimPrefix(digest, "sha256:")
+		path := "/var/lib/registry/docker/registry/v2/blobs/sha256/" + hex[:2] + "/" + hex + "/data"
+		return exec.Command("docker", "exec", container, "test", "-f", path).Run() == nil
+	}
+	if onDisk(firstDigest) {
+		t.Errorf("the replaced snapshot %s is still in the store after collection; nothing would ever take it", firstDigest)
+	}
+	if !onDisk(secondDigest) {
+		t.Errorf("the collector took the newest snapshot %s", secondDigest)
+	}
+	if !strings.HasPrefix(secondDigest, "sha256:") {
+		t.Errorf("the digest said %q", secondDigest)
+	}
+}
+
+// A store with no address is said, not dialled.
+func TestADocumentWithNowhereToGoIsRefusedByName(t *testing.T) {
+	if _, err := (Store{}).PutTagged(context.Background(), "facts", "latest", "x", []byte("{}")); err == nil ||
+		!strings.Contains(err.Error(), "no artifact store") {
+		t.Errorf("put with no store said %v", err)
+	}
+	if _, _, err := (Store{}).GetTagged(context.Background(), "facts", "latest"); err == nil ||
+		!strings.Contains(err.Error(), "no artifact store") {
+		t.Errorf("read with no store said %v", err)
+	}
+}

internal/facts/facts.go

@@ -0,0 +1,334 @@
+// Package facts is the mesh's facts snapshot: what a check needs to judge a change against the mesh
+// that runs, and nothing it could leak (novox/hq to-be 45 §9, ADR 0227 rule 9).
+//
+// **Why it exists.** Every check the mesh had was right about the world it was given, and none was
+// given the mesh's world: a module passed every test and refused the anchor's whole declaration because
+// a real machine's name made its identity 23 characters (issue 263); a manifest passed the catalogue
+// check and was refused by the node-engine (issue 236); a resolver answer that glibc forgave was final
+// to musl (issue 262). The controller holds those facts. It writes them here, the build seat reads them,
+// and a merge check composes every machine of the snapshot with the change applied.
+//
+// **What it holds, and what it never holds.** Every machine — under a stable pseudonym of the same length
+// as its name, because the length is what a name limit meets — with its roles, system, C library,
+// architecture, builds, what it reported it can do, what is assigned there, its pins and settings;
+// every seat and its holders; every module the mesh holds, as its manifest; the sources the mesh built
+// them from; the versions of the bus, the store and the node-engine it runs; and how each machine's
+// declaration composes today. **No secret and no address**: a setting whose key or value reads as a
+// secret is withheld, an address is replaced by one from a documentation range, and a machine's name, a
+// site, an account and a public domain are replaced wherever they appear. So a snapshot can be copied
+// into a test, a replay or a pull request without carrying anything of the installation it came from.
+package facts
+
+import (
+	"crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"sort"
+	"time"
+)
+
+// Format is the snapshot's version. A reader refuses one newer than it knows: a field it cannot read
+// is a fact it would judge without.
+const Format = 1
+
+// Repository and Tag are where the controller keeps the newest snapshot in the artifact store, and
+// MediaType what it is kept as.
+const (
+	Repository = "facts"
+	Tag        = "latest"
+	MediaType  = "application/vnd.novox.mesh.facts.v1+json"
+)
+
+// Facts is one snapshot.
+type Facts struct {
+	Format int `json:"facts"`
+	// Taken is when the controller composed it.
+	Taken time.Time `json:"taken"`
+	// Controller is the controller build that composed it — the one the mesh runs, which is the one a
+	// change to the catalogue must be readable by (version skew).
+	Controller Build `json:"controller"`
+	// Versions are what the mesh runs of the things its tests stand in for.
+	Versions Versions `json:"versions"`
+	// Sources are the repositories the mesh builds modules from, each with the newest commit it built.
+	Sources []Source `json:"sources"`
+	// Machines, in name order of their pseudonyms.
+	Machines []Machine `json:"machines"`
+	// Seats are every seat held, with its holders.
+	Seats []Seat `json:"seats"`
+	// Modules are every module the mesh holds, as it holds them.
+	Modules []Module `json:"modules"`
+	// Settings are the mesh-wide layer of every module's settings, scrubbed.
+	Settings []Settings `json:"settings,omitempty"`
+	// Edges are the build dependencies between modules, as the mesh recorded them — what a merge's
+	// rebuild width is computed from.
+	Edges []Edge `json:"edges,omitempty"`
+}
+
+// Build names one build of a core component.
+type Build struct {
+	Version string `json:"version,omitempty"`
+	Commit  string `json:"commit,omitempty"`
+}
+
+// Versions are what the mesh runs.
+type Versions struct {
+	// Bus is the bus server's release, as the server tells a client that connects.
+	Bus string `json:"bus,omitempty"`
+	// Store is the store's server version, as the store answers it.
+	Store string `json:"store,omitempty"`
+	// NodeEngines are the node-engine builds the machines report, each once.
+	NodeEngines []string `json:"node-engines,omitempty"`
+}
+
+// Source is a repository the mesh builds from, and the newest commit it built a module of.
+type Source struct {
+	Repository string `json:"repository"`
+	Commit     string `json:"commit,omitempty"`
+	Modules    int    `json:"modules"`
+}
+
+// Machine is one machine, under its pseudonym.
+type Machine struct {
+	Name string `json:"name"`
+	// Length is the length of its real name, which the pseudonym keeps.
+	Length int `json:"length"`
+	// Roles are what it is to the mesh, in words: the control node, the hub, the bus's machine, a
+	// holder of a mesh seat. What a check names when it fails one.
+	Roles []string `json:"roles,omitempty"`
+	// System is the node-engine's system (arch, alpine, …), Libc its C library, as far as the mesh knows.
+	System       string `json:"system,omitempty"`
+	Libc         string `json:"libc,omitempty"`
+	Architecture string `json:"architecture,omitempty"`
+	Kernel       string `json:"kernel,omitempty"`
+	// NodeEngine and NodeTools are the builds it runs.
+	NodeEngine string `json:"node-engine,omitempty"`
+	NodeTools  string `json:"node-tools,omitempty"`
+	// Capabilities are what it reported it can do; the detail kept only where it is a version.
+	Capabilities []Capability `json:"capabilities,omitempty"`
+	// Site, Hub, Public: where it is on the private network — its site (a pseudonym), whether it is the
+	// hub, whether others can dial it. No address.
+	Site   string `json:"site,omitempty"`
+	Hub    bool   `json:"hub,omitempty"`
+	Public bool   `json:"public,omitempty"`
+	// OnNetwork is whether it has a place on the private network at all.
+	OnNetwork bool `json:"on-network,omitempty"`
+	// Adopted is whether the mesh adopted it rather than converged it.
+	Adopted bool `json:"adopted,omitempty"`
+	// Account is the operator's login there (a pseudonym of the same length), and AccountHome where its
+	// home is when that is not the derived one.
+	Account     string `json:"account,omitempty"`
+	AccountHome string `json:"account-home,omitempty"`
+	// PublicDomain is the domain it answers for, its labels replaced.
+	PublicDomain string `json:"public-domain,omitempty"`
+	// Assigned is every module assigned there.
+	Assigned []string `json:"assigned,omitempty"`
+	// Pins are where it was told a provision comes from.
+	Pins []Pin `json:"pins,omitempty"`
+	// Settings are its own layer of each module's settings, scrubbed.
+	Settings []Settings `json:"settings,omitempty"`
+	// Accepted are the secrets a person gave the mesh for modules here, by name only: the mesh cannot
+	// make them, so a check composing this machine gives each a stand-in instead of refusing it.
+	Accepted []Accepted `json:"accepted,omitempty"`
+	// Declaration is how its declaration composes today, as the controller that took this saw it.
+	Declaration Declaration `json:"declaration"`
+}
+
+// Capability is one thing a machine reported it can or cannot do.
+type Capability struct {
+	Name    string `json:"name"`
+	Present bool   `json:"present"`
+	Detail  string `json:"detail,omitempty"`
+}
+
+// Pin is one provision a machine was told where to take from.
+type Pin struct {
+	Provision string `json:"provision"`
+	Machine   string `json:"machine"`
+	Module    string `json:"module,omitempty"`
+}
+
+// Accepted is one secret a person gave: the module's own when Provider is empty, else the credential it
+// takes from that machine's provider under Local.
+type Accepted struct {
+	Module   string `json:"module"`
+	Name     string `json:"name"`
+	Provider string `json:"provider,omitempty"`
+	Local    string `json:"local,omitempty"`
+}
+
+// Settings is one layer of one module's settings.
+type Settings struct {
+	Module string         `json:"module"`
+	Values map[string]any `json:"values"`
+}
+
+// Declaration is how one machine's declaration composed when the snapshot was taken.
+type Declaration struct {
+	// Composes is whether it composed and the node-engine's validator took it.
+	Composes bool `json:"composes"`
+	// Digest is its body's digest — composed as the next push would, so it moves with what the mesh
+	// would send, and is not the digest of what was last sent.
+	Digest string `json:"digest,omitempty"`
+	// Resources are what it declares, as `type:id`, sorted.
+	Resources []string `json:"resources,omitempty"`
+	// Problems are why it does not compose or validate, scrubbed.
+	Problems []string `json:"problems,omitempty"`
+	// LeftOut are the modules assigned there and left out of it, each with why.
+	LeftOut map[string]string `json:"left-out,omitempty"`
+	// Withheld are the consumers its grants leave out because an identity overflows the provision's
+	// bound (ADR 0225), and Unbound the credentials on record for consumers bound elsewhere (issue 274),
+	// each said in words.
+	Withheld []string `json:"withheld,omitempty"`
+	Unbound  []string `json:"unbound,omitempty"`
+}
+
+// Seat is one seat and the machines holding it.
+type Seat struct {
+	Name    string   `json:"name"`
+	Scope   string   `json:"scope"`
+	Holders []Holder `json:"holders"`
+}
+
+// Holder is one module on one machine holding a seat.
+type Holder struct {
+	Machine string `json:"machine"`
+	Module  string `json:"module"`
+}
+
+// Module is one module the mesh holds.
+type Module struct {
+	Name string `json:"name"`
+	// Repository and Path are where it is built from; empty for one that came with the controller.
+	Repository string `json:"repository,omitempty"`
+	Path       string `json:"path,omitempty"`
+	// Commit is the commit the manifest the mesh holds was read at.
+	Commit string `json:"commit,omitempty"`
+	// Provided is a module that came with the controller rather than from a repository.
+	Provided bool `json:"provided,omitempty"`
+	// RollOut is its upgrade policy: rolled out when built, or recorded.
+	RollOut bool `json:"roll-out,omitempty"`
+	// Reads are the other repositories its build read source from.
+	Reads []string `json:"reads,omitempty"`
+	// Manifest is the module as the mesh holds it: artifacts resolved to the builds it runs.
+	Manifest json.RawMessage `json:"manifest"`
+}
+
+// Edge is one build dependency: From is built standing on To.
+type Edge struct {
+	From string `json:"from"`
+	To   string `json:"to"`
+	Kind string `json:"kind,omitempty"`
+}
+
+// Sorted puts every list in a fixed order, so two snapshots of one mesh are the same bytes apart from
+// when they were taken.
+func (f *Facts) Sorted() {
+	sort.Slice(f.Machines, func(i, j int) bool { return f.Machines[i].Name < f.Machines[j].Name })
+	for i := range f.Machines {
+		m := &f.Machines[i]
+		sort.Strings(m.Roles)
+		sort.Strings(m.Assigned)
+		sort.Slice(m.Capabilities, func(a, b int) bool { return m.Capabilities[a].Name < m.Capabilities[b].Name })
+		sort.Slice(m.Pins, func(a, b int) bool { return m.Pins[a].Provision < m.Pins[b].Provision })
+		sort.Slice(m.Settings, func(a, b int) bool { return m.Settings[a].Module < m.Settings[b].Module })
+		sort.Slice(m.Accepted, func(a, b int) bool {
+			x, y := m.Accepted[a], m.Accepted[b]
+			return x.Module+"\x00"+x.Name+"\x00"+x.Provider+"\x00"+x.Local < y.Module+"\x00"+y.Name+"\x00"+y.Provider+"\x00"+y.Local
+		})
+		sort.Strings(m.Declaration.Resources)
+	}
+	sort.Slice(f.Seats, func(i, j int) bool {
+		if f.Seats[i].Name != f.Seats[j].Name {
+			return f.Seats[i].Name < f.Seats[j].Name
+		}
+		return f.Seats[i].Scope < f.Seats[j].Scope
+	})
+	for i := range f.Seats {
+		h := f.Seats[i].Holders
+		sort.Slice(h, func(a, b int) bool {
+			if h[a].Machine != h[b].Machine {
+				return h[a].Machine < h[b].Machine
+			}
+			return h[a].Module < h[b].Module
+		})
+	}
+	sort.Slice(f.Modules, func(i, j int) bool { return f.Modules[i].Name < f.Modules[j].Name })
+	sort.Slice(f.Sources, func(i, j int) bool { return f.Sources[i].Repository < f.Sources[j].Repository })
+	sort.Slice(f.Settings, func(i, j int) bool { return f.Settings[i].Module < f.Settings[j].Module })
+	sort.Slice(f.Edges, func(i, j int) bool {
+		if f.Edges[i].From != f.Edges[j].From {
+			return f.Edges[i].From < f.Edges[j].From
+		}
+		return f.Edges[i].To < f.Edges[j].To
+	})
+	sort.Strings(f.Versions.NodeEngines)
+}
+
+// Encode is the snapshot as it is kept: sorted, indented, so a person can read the one the build seat
+// read and a diff of two says what moved.
+func (f Facts) Encode() ([]byte, error) {
+	f.Sorted()
+	return json.MarshalIndent(f, "", " ")
+}
+
+// Content is the digest of everything but when it was taken: two snapshots of an unchanged mesh have
+// the same content, which is how the controller tells a change from another day.
+func (f Facts) Content() (string, error) {
+	f.Taken = time.Time{}
+	body, err := f.Encode()
+	if err != nil {
+		return "", err
+	}
+	sum := sha256.Sum256(body)
+	return fmt.Sprintf("sha256:%x", sum), nil
+}
+
+// Decode reads a snapshot, refusing one newer than this reader knows and one that is not a snapshot.
+func Decode(body []byte) (Facts, error) {
+	var f Facts
+	if err := json.Unmarshal(body, &f); err != nil {
+		return Facts{}, fmt.Errorf("not a facts snapshot: %w", err)
+	}
+	switch {
+	case f.Format == 0:
+		return Facts{}, fmt.Errorf("not a facts snapshot: it says no format")
+	case f.Format > Format:
+		return Facts{}, fmt.Errorf("a facts snapshot of format %d, and this reads format %d: a newer controller "+
+			"took it, and what it says beyond %d would be judged without", f.Format, Format, Format)
+	}
+	return f, nil
+}
+
+// Longest is the length of the longest machine name in the snapshot — what a consumer's identity is
+// judged on (novox/hq ADR 0225).
+func (f Facts) Longest() int {
+	longest := 0
+	for _, m := range f.Machines {
+		if m.Length > longest {
+			longest = m.Length
+		}
+	}
+	return longest
+}
+
+// Machine is the machine of that pseudonym.
+func (f Facts) Machine(name string) (Machine, bool) {
+	for _, m := range f.Machines {
+		if m.Name == name {
+			return m, true
+		}
+	}
+	return Machine{}, false
+}
+
+// Described is how a check names a machine: its roles, then its pseudonym.
+func (m Machine) Described() string {
+	if len(m.Roles) == 0 {
+		return "a machine (" + m.Name + ")"
+	}
+	out := m.Roles[0]
+	for _, r := range m.Roles[1:] {
+		out += ", " + r
+	}
+	return out + " (" + m.Name + ")"
+}

internal/facts/facts_test.go

@@ -0,0 +1,159 @@
+package facts
+
+import (
+	"fmt"
+	"net"
+	"regexp"
+	"strings"
+	"testing"
+	"time"
+)
+
+// A pseudonym keeps what a limit meets — the length, and letters where letters were — and nothing else.
+func TestAPseudonymKeepsTheLengthAndShapeAndIsStable(t *testing.T) {
+	for _, name := range []string{"ace", "g14", "novox", "shanks", "home-server", "a"} {
+		p := Pseudonym("machine", name)
+		if len(p) != len(name) {
+			t.Errorf("%s became %s: %d characters for %d", name, p, len(p), len(name))
+		}
+		if p == name {
+			t.Errorf("%s was kept as itself", name)
+		}
+		if p != Pseudonym("machine", name) {
+			t.Errorf("%s is not stable", name)
+		}
+		for i := range name {
+			isLetter := func(c byte) bool { return c >= 'a' && c <= 'z' }
+			isDigit := func(c byte) bool { return c >= '0' && c <= '9' }
+			if isLetter(name[i]) != isLetter(p[i]) || isDigit(name[i]) != isDigit(p[i]) {
+				t.Errorf("%s became %s: the shape moved at %d", name, p, i)
+			}
+		}
+	}
+	if Pseudonym("machine", "ace") == Pseudonym("site", "ace") {
+		t.Error("a site and a machine of one name share a pseudonym, so a snapshot says they are one thing")
+	}
+}
+
+// Nothing of the installation survives the scrubber: names, domains, accounts, addresses, mail, secrets.
+func TestTheScrubberLeavesNothingOfTheInstallation(t *testing.T) {
+	s := NewScrubber()
+	machine := s.Machine("homeserver")
+	s.Account("jochens")
+	domain := s.Domain("zurag.be")
+	if len(domain) != len("zurag.be") || !strings.HasSuffix(domain, ".be") || domain == "zurag.be" {
+		t.Errorf("the domain became %q", domain)
+	}
+	in := map[string]any{
+		"hub":        "homeserver",
+		"listen":     "10.42.0.7:51820",
+		"upstream":   []any{"192.168.1.135", "fd00::1"},
+		"site":       "https://grafana.zurag.be/login",
+		"admin":      "jschoubben@gmail.com",
+		"home":       "/home/jochens/.ssh",
+		"api_key":    "sk-live-abcdef",
+		"nested":     map[string]any{"password": "hunter2", "port": float64(5432)},
+		"opaque":     "a8F3kQ9zL2mX7vB4nC6dE1rT5yU0iO8pA3sD",
+		"dsn":        "postgres://app:s3cr3tpass@db.internal:5432/app",
+		"pem":        "-----BEGIN PRIVATE KEY-----\nMIIB",
+		"plain":      "a-long-plain-module-directory-name",
+		"digest":     "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
+		"version":    "2.11.17",
+		"homeserver": true,
+	}
+	out := s.Values(in)
+	flat := flatten(out)
+	for _, leaked := range []string{"homeserver\"", "10.42.0.7", "192.168.1.135", "fd00::1", "zurag", "jschoubben",
+		"gmail", "jochens", "sk-live", "hunter2", "a8F3kQ9zL2mX7vB4nC6dE1rT5yU0iO8pA3sD", "s3cr3tpass", "MIIB"} {
+		if strings.Contains(flat, leaked) {
+			t.Errorf("%q survived the scrubber:\n%s", leaked, flat)
+		}
+	}
+	if out["hub"] != machine {
+		t.Errorf("a machine named in a setting became %v, not its pseudonym %s", out["hub"], machine)
+	}
+	for _, kept := range []string{"a-long-plain-module-directory-name", "2.11.17", "sha256:44136fa3", "5432"} {
+		if !strings.Contains(flat, kept) {
+			t.Errorf("%q was scrubbed, and it is not the installation's:\n%s", kept, flat)
+		}
+	}
+	// Every address left is a documentation address.
+	for _, a := range regexp.MustCompile(`[0-9a-f:.]{7,}`).FindAllString(flat, -1) {
+		ip := net.ParseIP(strings.Trim(a, ".:"))
+		if ip == nil {
+			continue
+		}
+		doc := false
+		for _, cidr := range []string{"192.0.2.0/24", "198.51.100.0/24", "203.0.113.0/24", "2001:db8::/32"} {
+			_, n, _ := net.ParseCIDR(cidr)
+			doc = doc || n.Contains(ip)
+		}
+		if !doc {
+			t.Errorf("%s is not a documentation address", a)
+		}
+	}
+	// The same address is always the same stand-in.
+	if s.Text("10.42.0.7") != s.Text("at 10.42.0.7")[3:] {
+		t.Error("one address became two stand-ins")
+	}
+}
+
+func flatten(v any) string {
+	var b strings.Builder
+	var walk func(any)
+	walk = func(v any) {
+		switch t := v.(type) {
+		case map[string]any:
+			for k, e := range t {
+				b.WriteString(k + "\"=")
+				walk(e)
+				b.WriteString("\n")
+			}
+		case []any:
+			for _, e := range t {
+				walk(e)
+				b.WriteString(",")
+			}
+		case string:
+			b.WriteString(t + "\"")
+		default:
+			b.WriteString(fmt.Sprint(t))
+		}
+	}
+	walk(v)
+	return b.String()
+}
+
+// Two snapshots of one mesh, taken apart, are one content.
+func TestASnapshotOfAnUnchangedMeshIsTheSameContentAnotherDay(t *testing.T) {
+	f := Facts{Format: Format, Taken: time.Now(), Machines: []Machine{{Name: "b"}, {Name: "a"}}}
+	g := f
+	g.Taken = f.Taken.Add(24 * time.Hour)
+	g.Machines = []Machine{{Name: "a"}, {Name: "b"}}
+	a, err := f.Content()
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, _ := g.Content()
+	if a != b {
+		t.Error("the same mesh a day later reads as a change")
+	}
+	g.Machines = append(g.Machines, Machine{Name: "c"})
+	if c, _ := g.Content(); c == a {
+		t.Error("a machine added reads as no change")
+	}
+}
+
+// A reader refuses a snapshot it cannot read whole.
+func TestANewerSnapshotIsRefusedNotHalfRead(t *testing.T) {
+	if _, err := Decode([]byte(`{"facts": 99}`)); err == nil || !strings.Contains(err.Error(), "newer controller") {
+		t.Errorf("a newer format read as %v", err)
+	}
+	if _, err := Decode([]byte(`{"machines": []}`)); err == nil {
+		t.Error("a document with no format read as a snapshot")
+	}
+	f, err := Decode([]byte(`{"facts": 1, "machines": [{"name": "abc", "length": 3}, {"name": "defgh", "length": 5}]}`))
+	if err != nil || f.Longest() != 5 {
+		t.Errorf("read %+v, %v", f, err)
+	}
+}

internal/facts/scrub.go

@@ -0,0 +1,317 @@
+package facts
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"net"
+	"regexp"
+	"sort"
+	"strings"
+)
+
+// Withheld is what a value that reads as a secret becomes. A check composing with it gets a stand-in of
+// the right kind (a string), never the value.
+const Withheld = "withheld"
+
+// Pseudonym is the stable stand-in for a name: the same length, letters for letters and digits for
+// digits, anything else kept where it was. Stable, so two snapshots of one mesh name a machine alike and
+// a check's verdict can be compared across them; derived from the name alone, so it needs no key to be
+// kept anywhere.
+//
+// It hides nothing from somebody who can guess the names: that is not its purpose. Its purpose is that a
+// snapshot — and every fixture, replay or pull-request comment made from one — carries no name of the
+// installation it came from, while every length a limit meets stays the length it was.
+func Pseudonym(kind, name string) string {
+	sum := sha256.Sum256([]byte("novox-mesh-facts\x00" + kind + "\x00" + name))
+	out := []byte(name)
+	for i, c := range out {
+		b := sum[i%len(sum)] ^ byte(i/len(sum))
+		switch {
+		case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z':
+			out[i] = 'a' + b%26
+		case c >= '0' && c <= '9':
+			out[i] = '0' + b%10
+		}
+	}
+	// A name must still read as one: a machine's begins with a letter.
+	if len(out) > 0 && (out[0] < 'a' || out[0] > 'z') && name[0] >= 'a' && name[0] <= 'z' {
+		out[0] = 'a' + sum[0]%26
+	}
+	return string(out)
+}
+
+// Scrubber replaces what a snapshot must not carry, wherever it appears in text.
+type Scrubber struct {
+	// replace is every real word and what it becomes, longest first, so a domain is replaced before a
+	// label inside it.
+	replace [][2]string
+	seen    map[string]bool
+}
+
+// NewScrubber knows the installation's names: machines, sites, accounts, public domains.
+func NewScrubber() *Scrubber { return &Scrubber{seen: map[string]bool{}} }
+
+// Machine registers a machine's name and answers its pseudonym.
+func (s *Scrubber) Machine(name string) string { return s.word("machine", name) }
+
+// Site registers a site's name and answers its pseudonym.
+func (s *Scrubber) Site(name string) string { return s.word("site", name) }
+
+// Account registers an account's name and answers its pseudonym.
+func (s *Scrubber) Account(name string) string { return s.word("account", name) }
+
+// Domain registers a public domain and answers its stand-in: each label but the last replaced, so the
+// shape and every length stay.
+func (s *Scrubber) Domain(domain string) string {
+	if domain == "" {
+		return ""
+	}
+	labels := strings.Split(domain, ".")
+	for i := range labels {
+		if i == len(labels)-1 && len(labels) > 1 {
+			break
+		}
+		labels[i] = Pseudonym("domain", labels[i])
+	}
+	out := strings.Join(labels, ".")
+	s.add(domain, out)
+	return out
+}
+
+func (s *Scrubber) word(kind, name string) string {
+	if name == "" {
+		return ""
+	}
+	out := Pseudonym(kind, name)
+	s.add(name, out)
+	return out
+}
+
+func (s *Scrubber) add(from, to string) {
+	if from == "" || s.seen[from] {
+		return
+	}
+	s.seen[from] = true
+	s.replace = append(s.replace, [2]string{from, to})
+	sort.SliceStable(s.replace, func(i, j int) bool { return len(s.replace[i][0]) > len(s.replace[j][0]) })
+}
+
+// wordBoundary is what may stand beside a name for it to be that name and not part of another word.
+func wordBoundary(c byte) bool {
+	return !(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || c == '_')
+}
+
+// Text is s with every known name replaced, every address put in a documentation range, every address
+// of mail replaced, and every run that reads as a secret withheld.
+func (s *Scrubber) Text(text string) string {
+	if text == "" {
+		return text
+	}
+	text = secretRuns(text)
+	text = emails.ReplaceAllStringFunc(text, func(mail string) string {
+		if strings.HasPrefix(mail, Withheld+"@") {
+			return mail // a URL's withheld credentials, not an address of mail
+		}
+		return "someone@example.org"
+	})
+	text = addresses(text)
+	for _, r := range s.replace {
+		text = replaceWord(text, r[0], r[1])
+	}
+	return text
+}
+
+// replaceWord replaces from where it stands as a word of its own.
+func replaceWord(text, from, to string) string {
+	var b strings.Builder
+	for {
+		i := strings.Index(text, from)
+		if i < 0 {
+			b.WriteString(text)
+			return b.String()
+		}
+		end := i + len(from)
+		if (i == 0 || wordBoundary(text[i-1])) && (end == len(text) || wordBoundary(text[end])) {
+			b.WriteString(text[:i])
+			b.WriteString(to)
+		} else {
+			b.WriteString(text[:end])
+		}
+		text = text[end:]
+	}
+}
+
+// Values is a settings layer with every key that names a secret withheld, and every string scrubbed.
+func (s *Scrubber) Values(values map[string]any) map[string]any {
+	out := make(map[string]any, len(values))
+	for k, v := range values {
+		// A key may itself be a name — a map of machines to something.
+		key := s.Text(k)
+		if secretKey.MatchString(k) {
+			out[key] = withheldLike(v)
+			continue
+		}
+		out[key] = s.value(v)
+	}
+	return out
+}
+
+func (s *Scrubber) value(v any) any {
+	switch t := v.(type) {
+	case string:
+		return s.Text(t)
+	case map[string]any:
+		return s.Values(t)
+	case []any:
+		out := make([]any, len(t))
+		for i, e := range t {
+			out[i] = s.value(e)
+		}
+		return out
+	default:
+		return v
+	}
+}
+
+// withheldLike is a stand-in of the same kind: a string for a string, a list for a list, so a check
+// composing a setting still finds the shape it expects.
+func withheldLike(v any) any {
+	switch t := v.(type) {
+	case nil:
+		return nil
+	case bool, float64, int, int64:
+		return t
+	case []any:
+		out := make([]any, len(t))
+		for i, e := range t {
+			out[i] = withheldLike(e)
+		}
+		return out
+	case map[string]any:
+		out := map[string]any{}
+		for k, e := range t {
+			out[k] = withheldLike(e)
+		}
+		return out
+	default:
+		return Withheld
+	}
+}
+
+// secretKey is a setting's key that names a secret.
+var secretKey = regexp.MustCompile(`(?i)(secret|passw|token|api[-_]?key|private[-_]?key|credential|bearer|cookie|salt|signing)`)
+
+// emails are addresses of mail: a person's name, or an installation's domain, in either half.
+var emails = regexp.MustCompile(`[A-Za-z0-9._%+\-]+@[A-Za-z0-9.\-]+\.[A-Za-z]{2,}`)
+
+// secretRun is a run of characters a key, a token or a hash is made of, long enough to be one.
+var secretRun = regexp.MustCompile(`[A-Za-z0-9+/=_\-]{24,}`)
+
+// userinfo is the credentials part of a URL.
+var userinfo = regexp.MustCompile(`(://)[^/@\s:]+:[^/@\s]+@`)
+
+// secretRuns withholds a URL's credentials and every run that reads as a key: long, and mixing letters
+// with digits or symbols. A long plain word (a path, a module's name) is left alone.
+func secretRuns(text string) string {
+	if strings.Contains(text, "-----BEGIN") {
+		return Withheld
+	}
+	text = userinfo.ReplaceAllString(text, "${1}"+Withheld+"@")
+	var b strings.Builder
+	last := 0
+	for _, at := range secretRun.FindAllStringIndex(text, -1) {
+		run := text[at[0]:at[1]]
+		b.WriteString(text[last:at[0]])
+		last = at[1]
+		// A digest names an artifact, not a secret.
+		if strings.HasSuffix(text[:at[0]], "sha256:") {
+			b.WriteString(run)
+			continue
+		}
+		b.WriteString(judgeRun(run))
+	}
+	b.WriteString(text[last:])
+	return b.String()
+}
+
+// judgeRun is a run withheld when it reads as a key: long, and mixing letters with digits or symbols.
+func judgeRun(run string) string {
+	{
+		var lower, upper, digit, symbol bool
+		for _, c := range run {
+			switch {
+			case c >= 'a' && c <= 'z':
+				lower = true
+			case c >= 'A' && c <= 'Z':
+				upper = true
+			case c >= '0' && c <= '9':
+				digit = true
+			default:
+				symbol = true
+			}
+		}
+		classes := 0
+		for _, b := range []bool{lower, upper, digit, symbol} {
+			if b {
+				classes++
+			}
+		}
+		// A sha256 digest names an artifact, not a secret, and a dashed word is a name.
+		if strings.HasPrefix(run, "sha256") || (!digit && !upper) {
+			return run
+		}
+		if classes >= 3 || (digit && (lower || upper) && len(run) >= 32) {
+			return Withheld
+		}
+		return run
+	}
+}
+
+// addresses puts every IP address in text into a documentation range (RFC 5737, RFC 3849): the same
+// address always becomes the same stand-in, so two settings naming one machine still name one.
+func addresses(text string) string {
+	var b strings.Builder
+	i := 0
+	for i < len(text) {
+		if !addressChar(text[i]) {
+			b.WriteByte(text[i])
+			i++
+			continue
+		}
+		j := i
+		for j < len(text) && addressChar(text[j]) {
+			j++
+		}
+		b.WriteString(standIn(text[i:j]))
+		i = j
+	}
+	return b.String()
+}
+
+func addressChar(c byte) bool {
+	return c >= '0' && c <= '9' || c >= 'a' && c <= 'f' || c >= 'A' && c <= 'F' || c == '.' || c == ':'
+}
+
+// standIn is the documentation address for a run that is an address, or the run itself.
+func standIn(run string) string {
+	trimmed := strings.TrimRight(run, ".:")
+	tail := run[len(trimmed):]
+	ip := net.ParseIP(trimmed)
+	switch {
+	case ip == nil:
+		// A port after an IPv4 address reads as part of the run: try without it.
+		if host, port, ok := strings.Cut(trimmed, ":"); ok && strings.Count(trimmed, ":") == 1 &&
+			net.ParseIP(host) != nil && strings.Contains(host, ".") {
+			return standIn(host) + ":" + port + tail
+		}
+		return run
+	case ip.To4() != nil && strings.Contains(trimmed, "."):
+		sum := sha256.Sum256([]byte("v4\x00" + trimmed))
+		ranges := []string{"192.0.2", "198.51.100", "203.0.113"}
+		return fmt.Sprintf("%s.%d", ranges[sum[0]%3], 1+sum[1]%254) + tail
+	case strings.Count(trimmed, ":") >= 2:
+		sum := sha256.Sum256([]byte("v6\x00" + trimmed))
+		return fmt.Sprintf("2001:db8::%x:%x", uint16(sum[0])<<8|uint16(sum[1]), uint16(sum[2])<<8|uint16(sum[3])) + tail
+	}
+	return run
+}

internal/inventory/reported.go

@@ -0,0 +1,42 @@
+package inventory
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// Described is what a machine said about itself beyond its capabilities: the architecture and kernel
+// its node-engine runs on (novox/hq to-be 45 §9, the facts snapshot).
+type Described struct {
+	Architecture string `json:"architecture"`
+	Kernel       string `json:"kernel"`
+}
+
+// DescribedOf is the architecture and kernel a machine last reported; empty for one that never has.
+func (i *Inventory) DescribedOf(ctx context.Context, nodeName string) (Described, error) {
+	var raw []byte
+	err := i.store.Pool().QueryRow(ctx, `select profile from node where name = $1`, nodeName).Scan(&raw)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return Described{}, fmt.Errorf("%w: %s", ErrNoSuchNode, nodeName)
+	}
+	if err != nil || len(raw) == 0 {
+		return Described{}, err
+	}
+	var r Described
+	if err := json.Unmarshal(raw, &r); err != nil {
+		return Described{}, err
+	}
+	return r, nil
+}
+
+// ServerVersion is the store's own word for the release it runs — the version a test suite standing in
+// for it must run (novox/hq ADR 0227 rule 9).
+func (i *Inventory) ServerVersion(ctx context.Context) (string, error) {
+	var v string
+	err := i.store.Pool().QueryRow(ctx, `show server_version`).Scan(&v)
+	return v, err
+}