feat(registry): api 定期删除无引用 manifest，gate 提供 manifest 索引

cmd/felis/api.go

@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"log/slog"
 	"net/http"
 	"os"
 	"regexp"
@@ -26,6 +27,7 @@ import (
 	"felis.lolicon.best/internal/passkey"
 	"felis.lolicon.best/internal/platform"
 	"felis.lolicon.best/internal/reaper"
+	"felis.lolicon.best/internal/registryprune"
 	"felis.lolicon.best/internal/restore"
 	"felis.lolicon.best/internal/store"
 	"felis.lolicon.best/internal/submit"
@@ -399,6 +401,10 @@ func cmdAPI(args []string, stdout, stderr io.Writer) int {
 	// reconciles it, but this loop converges builds nobody is polling.
 	go reconcileBuilds(ctx, builder, stderr)
 
+	if pruner := registryPruner(cfg, builder.Store, a.Cluster, stderr); pruner != nil {
+		go pruner.Loop(ctx, registryPruneInterval)
+	}
+
 	select {
 	case <-ctx.Done():
 		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
@@ -613,6 +619,80 @@ func reconcileBuilds(ctx context.Context, b *build.Builder, stderr io.Writer) {
 	}
 }
 
+// registryPruneInterval spaces the registry pruner's runs. The registry-gc
+// sidecar sweeps once a day, so pruning more often only changes which sweep frees
+// a layer.
+const registryPruneInterval = 6 * time.Hour
+
+// registryPruner deletes the registry manifests nothing references
+// (internal/registryprune); the registry-gc sidecar frees their layers on its next
+// sweep. It acts as the gate's prune principal, whose token the api Deployment
+// injects from felis-registry-auth. Without the token the registry only grows,
+// which is said once here.
+func registryPruner(cfg *config.Config, store imageRefStore, servers serverLister, stderr io.Writer) *registryprune.Pruner {
+	if cfg.Registry.URL == "" {
+		return nil
+	}
+	token := os.Getenv(platform.RegistryPruneTokenEnv)
+	if token == "" {
+		fmt.Fprintf(stderr, "felis api: registry pruner disabled (%s unset) — images nothing uses are never deleted from the registry\n", platform.RegistryPruneTokenEnv)
+		return nil
+	}
+	static := []string{
+		os.Getenv("FELIS_IMAGE"),
+		cfg.Registry.KanikoImage, cfg.Registry.TrivyImage,
+		cfg.Registry.TrivyDBRepository, cfg.Registry.TrivyJavaDBRepository,
+	}
+	return &registryprune.Pruner{
+		Registry: &registryprune.Client{Endpoint: "http://" + cfg.Registry.URL, Token: token},
+		Host:     cfg.Registry.URL,
+		Refs: func(ctx context.Context) ([]string, error) {
+			return inUseImageRefs(ctx, store, servers, static)
+		},
+		Log: slog.New(slog.NewTextHandler(stderr, nil)),
+	}
+}
+
+type imageRefStore interface {
+	ListImages(ctx context.Context) ([]build.Image, error)
+	ListUnfinishedBuilds(ctx context.Context) ([]build.Build, error)
+}
+
+type serverLister interface {
+	ListServers(ctx context.Context) ([]api.ServerInfo, error)
+}
+
+// inUseImageRefs lists every image reference the platform still depends on: the
+// whitelist (disabled rows too, an admin may enable them again), every server's
+// spec, builds still running, and the images the control plane and the build
+// Jobs run. Any source failing fails the whole list, so the pruner never decides
+// on a partial view.
+func inUseImageRefs(ctx context.Context, store imageRefStore, servers serverLister, static []string) ([]string, error) {
+	refs := append([]string(nil), static...)
+	images, err := store.ListImages(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("image whitelist: %w", err)
+	}
+	for _, img := range images {
+		refs = append(refs, img.ImageRef)
+	}
+	srvs, err := servers.ListServers(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("servers: %w", err)
+	}
+	for _, s := range srvs {
+		refs = append(refs, s.Image)
+	}
+	builds, err := store.ListUnfinishedBuilds(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("running builds: %w", err)
+	}
+	for _, b := range builds {
+		refs = append(refs, b.ImageRef)
+	}
+	return refs, nil
+}
+
 // mailLimit turns smtp.max_per_hour into the API's install-wide mail bucket:
 // the hourly cap as the refill rate, with a quarter of it (at least 5) allowed
 // at once so a burst of real sign-ins is not queued behind the average.

cmd/felis/api_test.go

@@ -1,9 +1,14 @@
 package main
 
 import (
+	"context"
+	"errors"
+	"fmt"
 	"net/http"
 	"testing"
 
+	"felis.lolicon.best/internal/api"
+	"felis.lolicon.best/internal/build"
 	"felis.lolicon.best/internal/config"
 )
 
@@ -91,3 +96,47 @@ func TestNewAPIServerSetsHardenedTimeouts(t *testing.T) {
 		t.Errorf("ReadTimeout = %v, want 0 (unset) so a slow SSE attach is not capped", srv.ReadTimeout)
 	}
 }
+
+type fakeRefStore struct {
+	images []build.Image
+	builds []build.Build
+	err    error
+}
+
+func (f fakeRefStore) ListImages(context.Context) ([]build.Image, error) { return f.images, f.err }
+func (f fakeRefStore) ListUnfinishedBuilds(context.Context) ([]build.Build, error) {
+	return f.builds, nil
+}
+
+type fakeServers []api.ServerInfo
+
+func (f fakeServers) ListServers(context.Context) ([]api.ServerInfo, error) { return f, nil }
+
+// The registry pruner deletes whatever this list does not name, so every source of
+// a reference has to be in it, and a failing source must fail the list.
+func TestInUseImageRefsCoversEverySource(t *testing.T) {
+	const reg = "registry.felis.svc:5000/"
+	store := fakeRefStore{
+		images: []build.Image{{ImageRef: reg + "modpacks/pack:*"}, {ImageRef: reg + "felis/paper:demo"}},
+		builds: []build.Build{{ImageRef: reg + "user-uploads/sub-9:latest"}},
+	}
+	servers := fakeServers{{Name: "s1", Image: reg + "felis/paper:demo@sha256:" + fmt.Sprintf("%064d", 1)}}
+	got, err := inUseImageRefs(context.Background(), store, servers, []string{reg + "felis/felis:b60"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []string{
+		reg + "felis/felis:b60",
+		reg + "modpacks/pack:*", reg + "felis/paper:demo",
+		reg + "felis/paper:demo@sha256:" + fmt.Sprintf("%064d", 1),
+		reg + "user-uploads/sub-9:latest",
+	}
+	if fmt.Sprint(got) != fmt.Sprint(want) {
+		t.Fatalf("refs = %v\nwant %v", got, want)
+	}
+
+	store.err = errors.New("db down")
+	if _, err := inUseImageRefs(context.Background(), store, servers, nil); err == nil {
+		t.Fatal("a failing whitelist read produced a reference list")
+	}
+}

cmd/felis/registrygate.go

@@ -44,6 +44,7 @@ func cmdRegistryGate(args []string, _, stderr io.Writer) int {
 	maintListen := fs.String("maint-listen", "", "loopback address for the GC sidecar's read-only handshake (empty disables it)")
 	maintDir := fs.String("maint-dir", "", "directory that keeps an open read-only window across a gate restart")
 	quiet := fs.Duration("maint-quiet", registrygate.DefaultQuiet, "how long writes must be idle before a read-only window is granted")
+	dataDir := fs.String("data-dir", "", "the registry's storage root, mounted read-only, for the manifest index (empty disables it)")
 	if err := fs.Parse(args); err != nil {
 		return 2
 	}
@@ -70,6 +71,7 @@ func cmdRegistryGate(args []string, _, stderr io.Writer) int {
 
 	gate := registrygate.New(target, tokens, log)
 	gate.SetQuiet(*quiet)
+	gate.DataDir = *dataDir
 	if *maintDir != "" {
 		if err := gate.SetMaintenanceState(registrygate.MaintStatePath(*maintDir)); err != nil {
 			// A corrupt file must not keep the registry from serving pulls.

deploy/bootstrap.sh

@@ -411,10 +411,12 @@ apply_registry_secrets() {
   remember_temp "$dir"
   printf '%s' "$REGISTRY_PLATFORM_TOKEN" > "${dir}/platform"
   printf '%s' "$REGISTRY_BUILD_TOKEN" > "${dir}/build"
+  printf '%s' "$REGISTRY_PRUNE_TOKEN" > "${dir}/prune"
   printf '%s' build > "${dir}/username"
   kube -n "$CONTROL_NS" create secret generic felis-registry-auth \
     --from-file=platform="${dir}/platform" \
     --from-file=build="${dir}/build" \
+    --from-file=prune="${dir}/prune" \
     --dry-run=client -o yaml | kube apply -f -
   kube -n "$BUILD_NS" create secret generic felis-registry-push \
     --from-file=username="${dir}/username" \
@@ -2210,9 +2212,11 @@ load_or_make_secrets() {
   # Registry write credentials, one per principal the registry gate knows
   # (internal/registrygate): platform pushes the installer's own images and the
   # Trivy DB mirrors, build is what a build Job's push container presents and may
-  # never write under felis/ or mirror/. Reads stay anonymous.
+  # never write under felis/ or mirror/, prune is felis-api deleting manifests
+  # nothing references (internal/registryprune). Reads stay anonymous.
   REGISTRY_PLATFORM_TOKEN="${REGISTRY_PLATFORM_TOKEN:-$(openssl rand -hex 32)}"
   REGISTRY_BUILD_TOKEN="${REGISTRY_BUILD_TOKEN:-$(openssl rand -hex 32)}"
+  REGISTRY_PRUNE_TOKEN="${REGISTRY_PRUNE_TOKEN:-$(openssl rand -hex 32)}"
   (
     umask 077
     cat > "$SECRETS_ENV" <<EOF
@@ -2222,6 +2226,7 @@ SESSION_SECRET=${SESSION_SECRET}
 FORWARDING_SECRET=${FORWARDING_SECRET}
 REGISTRY_PLATFORM_TOKEN=${REGISTRY_PLATFORM_TOKEN}
 REGISTRY_BUILD_TOKEN=${REGISTRY_BUILD_TOKEN}
+REGISTRY_PRUNE_TOKEN=${REGISTRY_PRUNE_TOKEN}
 EOF
   )
   chmod 0600 "$SECRETS_ENV"

internal/naming/naming.go

@@ -72,8 +72,8 @@ const (
 )
 
 // Registry write credentials (internal/registrygate). The registry namespace holds
-// RegistryAuthSecretName with one key per principal (platform, build), mounted into
+// RegistryAuthSecretName with one key per principal (platform, build, prune),
-// the gate sidecar. The build namespace holds RegistryPushSecretName with the build
+// mounted into the gate sidecar; felis-api reads the prune key into env. The build namespace holds RegistryPushSecretName with the build
 // principal's username/password, read only by a build Job's push container. Both
 // are provisioned out-of-band by deploy/bootstrap.sh.
 const (

internal/platform/netpol.go

@@ -236,11 +236,13 @@ func loginToInternalAPI(p Params) *networkingv1.NetworkPolicy {
 
 // RegistryIngressPolicy fences the registry pod: only build pods and felis-api
 // reach its port. Build pods push what they build; felis-api reads a manifest
-// digest to pin a new server's image (internal/imagepin). Everything else that
+// digest to pin a new server's image (internal/imagepin) and deletes manifests
-// uses the registry runs on the node — containerd's pulls and the installer's
+// nothing references (internal/registryprune). Everything else that uses the
-// pushes both arrive through the loopback hostPort — and Kubernetes never blocks
+// registry runs on the node — containerd's pulls and the installer's pushes both
-// resident-node traffic. Write authorization is the gate's job (felis-api holds no
+// arrive through the loopback hostPort — and Kubernetes never blocks
-// registry credential); this policy keeps every other pod from even trying.
+// resident-node traffic. Write authorization is the gate's job (felis-api holds
+// only the prune principal, which can delete a manifest by digest and nothing
+// else); this policy keeps every other pod from even trying.
 func RegistryIngressPolicy(p Params) *networkingv1.NetworkPolicy {
 	p = p.withDefaults()
 	tcp := corev1.ProtocolTCP

internal/platform/workloads.go

@@ -151,6 +151,16 @@ const (
 	// [smtp] password_ref defaults to this name.
 	SMTPPasswordEnv = "FELIS_SMTP_PASSWORD"
 
+	// RegistryPruneTokenEnv carries the registry gate's prune principal token into
+	// felis-api, whose pruner deletes the manifests nothing references
+	// (internal/registryprune). It comes from the prune key of
+	// naming.RegistryAuthSecretName, optionally: that Secret lives in the registry
+	// namespace, which is the control namespace on every install the bootstrap
+	// makes, and an install that splits them or predates the key runs without the
+	// pruner.
+	RegistryPruneTokenEnv = "FELIS_REGISTRY_PRUNE_TOKEN"
+	registryPruneTokenKey = "prune"
+
 	// worldsMountPath is where the reaper CronJob mounts the worlds-root (read-only).
 	// It is the default of `felis reaper --worlds-root`; the resolver then reads each
 	// world at <worldsMountPath>/<pvc>. Single-sourced with cmd/felis/reaper.go.
@@ -339,6 +349,9 @@ func APIDeployment(p Params) *appsv1.Deployment {
 		corev1.EnvVar{Name: SMTPPasswordEnv, ValueFrom: &corev1.EnvVarSource{SecretKeyRef: &corev1.SecretKeySelector{
 			LocalObjectReference: corev1.LocalObjectReference{Name: SMTPSecretName}, Key: SMTPSecretPasswordKey, Optional: optional,
 		}}},
+		corev1.EnvVar{Name: RegistryPruneTokenEnv, ValueFrom: &corev1.EnvVarSource{SecretKeyRef: &corev1.SecretKeySelector{
+			LocalObjectReference: corev1.LocalObjectReference{Name: naming.RegistryAuthSecretName}, Key: registryPruneTokenKey, Optional: optional,
+		}}},
 	)
 
 	container := corev1.Container{
@@ -869,6 +882,8 @@ func registryDeployment(p Params) *appsv1.Deployment {
 			"--auth-dir=" + registryAuthMountPath,
 			fmt.Sprintf("--maint-listen=127.0.0.1:%d", registryMaintPort(p)),
 			"--maint-dir=" + registryMaintMountPath,
+			// The manifest index felis-api's pruner reads (registrygate/index.go).
+			"--data-dir=" + registryDataPath,
 		},
 		Ports: []corev1.ContainerPort{
 			{
@@ -881,6 +896,7 @@ func registryDeployment(p Params) *appsv1.Deployment {
 		VolumeMounts: []corev1.VolumeMount{
 			{Name: registryAuthVolume, MountPath: registryAuthMountPath, ReadOnly: true},
 			{Name: registryMaintVolume, MountPath: registryMaintMountPath},
+			{Name: registryVolume, MountPath: registryDataPath, ReadOnly: true},
 		},
 		// /healthz answers 200 only while registry:2 answers GET /v2/ on loopback,
 		// so a registry whose storage broke shows up as an unready pod instead of a

internal/platform/workloads_test.go

@@ -11,6 +11,8 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/util/intstr"
+
+	"felis.lolicon.best/internal/naming"
 )
 
 // podSpec returns the single container and the pod template of a Deployment,
@@ -289,6 +291,7 @@ func TestAPIDeployment_UploadsStorage(t *testing.T) {
 		{UploadsS3AccessKeyEnv, UploadsS3SecretName, UploadsS3SecretAccessKey},
 		{UploadsS3SecretKeyEnv, UploadsS3SecretName, UploadsS3SecretSecretKey},
 		{SMTPPasswordEnv, SMTPSecretName, SMTPSecretPasswordKey},
+		{RegistryPruneTokenEnv, naming.RegistryAuthSecretName, "prune"},
 	} {
 		e := envVar(c.Env, ev.name)
 		if e == nil || e.ValueFrom == nil || e.ValueFrom.SecretKeyRef == nil {
@@ -507,6 +510,7 @@ func TestRegistry_DeploymentServicePVC(t *testing.T) {
 		// The GC handshake has no authentication: loopback only.
 		fmt.Sprintf("--maint-listen=127.0.0.1:%d", p.RegistryPort+2),
 		"--maint-dir=" + registryMaintMountPath,
+		"--data-dir=" + registryDataPath,
 	} {
 		if !contains(gate.Args, want) {
 			t.Errorf("gate args = %v, want %s", gate.Args, want)
@@ -575,6 +579,12 @@ func TestRegistry_DeploymentServicePVC(t *testing.T) {
 			t.Error("registry:2 must not mount the write tokens")
 		}
 	}
+	// The gate reads the manifest index off the data volume, and never writes it.
+	for _, m := range gate.VolumeMounts {
+		if m.Name == registryVolume && !m.ReadOnly {
+			t.Error("the gate must mount the registry data read-only")
+		}
+	}
 	if !mounted {
 		t.Errorf("gate must mount the tokens read-only, mounts=%v", gate.VolumeMounts)
 	}

internal/registrygate/gate.go

@@ -69,6 +69,9 @@ type Gate struct {
 	Upstream *url.URL
 	// Log receives one line per refused write. Nil discards.
 	Log *slog.Logger
+	// DataDir is the registry's storage root, mounted read-only, for the manifest
+	// index (index.go). Empty turns the index off.
+	DataDir string
 
 	proxy  *httputil.ReverseProxy
 	health *http.Client
@@ -105,6 +108,10 @@ func (g *Gate) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		g.serveHealth(w, r)
 		return
 	}
+	if strings.HasPrefix(r.URL.Path, IndexPathPrefix) {
+		g.serveIndex(w, r)
+		return
+	}
 	if !strings.HasPrefix(r.URL.Path, "/v2/") && r.URL.Path != "/v2" {
 		writeError(w, http.StatusNotFound, "NAME_UNKNOWN", "not a registry API path")
 		return

internal/registrygate/index.go

@@ -0,0 +1,124 @@
+package registrygate
+
+import (
+	"encoding/json"
+	"errors"
+	"io/fs"
+	"net/http"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+	"time"
+)
+
+// IndexPathPrefix serves the manifest index of one repository:
+//
+//	GET /felis/manifests/<repo>  {"revisions":[{"digest":…,"pushed":…}],"tags":{"<tag>":"<digest>"}}
+//
+// The registry API can list a repository's tags but not its manifests, so a
+// manifest a tag moved off (every rebuild of :demo or :latest leaves one) is
+// invisible to it, while it still holds every layer it names. felis-api's pruner
+// needs the full set to decide which to delete; the gate reads it off the data
+// volume it mounts read-only, from the filesystem driver's layout that registry
+// 2.x and 3.x share. "pushed" is the modification time of the revision link, which
+// the registry rewrites on every push of that manifest.
+//
+// Anonymous like every read: a digest list says no more than tags/list and
+// _catalog already do.
+const IndexPathPrefix = "/felis/manifests/"
+
+// Index is the manifest index of one repository.
+type Index struct {
+	Revisions []Revision        `json:"revisions"`
+	Tags      map[string]string `json:"tags"`
+}
+
+// Revision is one manifest stored in a repository.
+type Revision struct {
+	Digest string    `json:"digest"`
+	Pushed time.Time `json:"pushed"`
+}
+
+// repoNameRE is the distribution reference grammar for a repository path. Every
+// component starts and ends alphanumeric, so no match can hold "." or "..".
+var repoNameRE = regexp.MustCompile(`^[a-z0-9]+(?:(?:[._]|__|[-]*)[a-z0-9]+)*(?:/[a-z0-9]+(?:(?:[._]|__|[-]*)[a-z0-9]+)*)*$`)
+
+var hexDigestRE = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+func (g *Gate) serveIndex(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		writeError(w, http.StatusMethodNotAllowed, "UNSUPPORTED", "method not allowed")
+		return
+	}
+	if g.DataDir == "" {
+		writeError(w, http.StatusNotFound, "UNSUPPORTED", "this gate does not mount the registry data")
+		return
+	}
+	repo := strings.TrimPrefix(r.URL.Path, IndexPathPrefix)
+	if r.URL.RawPath != "" || !repoNameRE.MatchString(repo) {
+		writeError(w, http.StatusBadRequest, "NAME_INVALID", "invalid repository name")
+		return
+	}
+	idx, err := ReadIndex(g.DataDir, repo)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "UNKNOWN", err.Error())
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(idx)
+}
+
+// ReadIndex reads repo's manifests and tags from a registry filesystem root. A
+// repository that does not exist has an empty index.
+func ReadIndex(root, repo string) (*Index, error) {
+	if !repoNameRE.MatchString(repo) {
+		return nil, errors.New("invalid repository name")
+	}
+	base := filepath.Join(root, "docker", "registry", "v2", "repositories", filepath.FromSlash(repo), "_manifests")
+	idx := &Index{Revisions: []Revision{}, Tags: map[string]string{}}
+
+	revDir := filepath.Join(base, "revisions", "sha256")
+	entries, err := os.ReadDir(revDir)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return nil, err
+	}
+	for _, e := range entries {
+		if !e.IsDir() || !hexDigestRE.MatchString(e.Name()) {
+			continue
+		}
+		// A deleted manifest keeps its directory and loses its link.
+		st, err := os.Stat(filepath.Join(revDir, e.Name(), "link"))
+		if errors.Is(err, fs.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return nil, err
+		}
+		idx.Revisions = append(idx.Revisions, Revision{Digest: "sha256:" + e.Name(), Pushed: st.ModTime().UTC()})
+	}
+	sort.Slice(idx.Revisions, func(i, j int) bool { return idx.Revisions[i].Digest < idx.Revisions[j].Digest })
+
+	tagDir := filepath.Join(base, "tags")
+	tags, err := os.ReadDir(tagDir)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return nil, err
+	}
+	for _, e := range tags {
+		if !e.IsDir() {
+			continue
+		}
+		b, err := os.ReadFile(filepath.Join(tagDir, e.Name(), "current", "link"))
+		if errors.Is(err, fs.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return nil, err
+		}
+		if d := strings.TrimSpace(string(b)); digestRE.MatchString(d) {
+			idx.Tags[e.Name()] = d
+		}
+	}
+	return idx, nil
+}

internal/registrygate/maint_test.go

@@ -1,6 +1,7 @@
 package registrygate
 
 import (
+	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -206,3 +207,72 @@ func TestReadOnlyWindowSurvivesAGateRestart(t *testing.T) {
 		t.Fatalf("a corrupt state file = %v, want an error naming it", err)
 	}
 }
+
+func TestManifestIndexListsUntaggedRevisions(t *testing.T) {
+	root := t.TempDir()
+	base := root + "/docker/registry/v2/repositories/felis/paper/_manifests"
+	hexA := strings.Repeat("a", 64)
+	hexB := strings.Repeat("b", 64)
+	hexGone := strings.Repeat("c", 64)
+	for _, h := range []string{hexA, hexB} {
+		if err := os.MkdirAll(base+"/revisions/sha256/"+h, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(base+"/revisions/sha256/"+h+"/link", []byte("sha256:"+h), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	// A deleted manifest leaves its directory without a link.
+	if err := os.MkdirAll(base+"/revisions/sha256/"+hexGone, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(base+"/tags/demo/current", 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(base+"/tags/demo/current/link", []byte("sha256:"+hexB), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	old := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	if err := os.Chtimes(base+"/revisions/sha256/"+hexA+"/link", old, old); err != nil {
+		t.Fatal(err)
+	}
+
+	up := httptest.NewServer(http.NotFoundHandler())
+	t.Cleanup(up.Close)
+	target, _ := url.Parse(up.URL)
+	g := New(target, nil, nil)
+	g.DataDir = root
+	srv := httptest.NewServer(g)
+	t.Cleanup(srv.Close)
+
+	resp, err := http.Get(srv.URL + IndexPathPrefix + "felis/paper")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	var idx Index
+	if err := json.NewDecoder(resp.Body).Decode(&idx); err != nil {
+		t.Fatal(err)
+	}
+	if len(idx.Revisions) != 2 || idx.Revisions[0].Digest != "sha256:"+hexA || !idx.Revisions[0].Pushed.Equal(old) {
+		t.Fatalf("revisions = %+v, want a (pushed %s) and b, without the deleted c", idx.Revisions, old)
+	}
+	if idx.Tags["demo"] != "sha256:"+hexB || len(idx.Tags) != 1 {
+		t.Fatalf("tags = %v, want demo -> b", idx.Tags)
+	}
+
+	// A repository that does not exist is empty; a traversal is refused.
+	if idx, err := ReadIndex(root, "user-uploads/none"); err != nil || len(idx.Revisions) != 0 || len(idx.Tags) != 0 {
+		t.Fatalf("missing repo = %+v, %v, want empty", idx, err)
+	}
+	for _, bad := range []string{"felis/../felis/paper", "felis/./paper", "Felis/paper", "felis//paper", "felis/paper/"} {
+		resp, err := http.Get(srv.URL + IndexPathPrefix + bad)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp.Body.Close()
+		if resp.StatusCode != http.StatusBadRequest {
+			t.Errorf("index of %q = %d, want 400", bad, resp.StatusCode)
+		}
+	}
+}

internal/registryprune/client.go

@@ -0,0 +1,115 @@
+package registryprune
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"felis.lolicon.best/internal/registrygate"
+)
+
+// Client talks to the registry through its gate: the catalog and the manifest
+// index anonymously, deletes as the prune principal.
+type Client struct {
+	// Endpoint is the gate's base URL, e.g. http://registry.felis.svc:5000.
+	Endpoint string
+	// Token is the prune principal's secret.
+	Token string
+	// HTTP makes the requests; nil uses a client with a 30s timeout.
+	HTTP *http.Client
+}
+
+func (c *Client) http() *http.Client {
+	if c.HTTP != nil {
+		return c.HTTP
+	}
+	return &http.Client{Timeout: 30 * time.Second}
+}
+
+// Repositories pages through /v2/_catalog.
+func (c *Client) Repositories(ctx context.Context) ([]string, error) {
+	var out []string
+	next := c.Endpoint + "/v2/_catalog?n=1000"
+	for next != "" {
+		var page struct {
+			Repositories []string `json:"repositories"`
+		}
+		resp, err := c.get(ctx, next, &page)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, page.Repositories...)
+		next = ""
+		// Link: </v2/_catalog?last=x&n=1000>; rel="next"
+		if link := resp.Header.Get("Link"); strings.Contains(link, `rel="next"`) {
+			start, end := strings.Index(link, "<"), strings.Index(link, ">")
+			if start < 0 || end <= start {
+				return nil, fmt.Errorf("malformed catalog Link header %q", link)
+			}
+			u, err := url.Parse(c.Endpoint)
+			if err != nil {
+				return nil, err
+			}
+			ref, err := url.Parse(link[start+1 : end])
+			if err != nil {
+				return nil, err
+			}
+			next = u.ResolveReference(ref).String()
+		}
+	}
+	return out, nil
+}
+
+// Index reads the gate's manifest index of repo.
+func (c *Client) Index(ctx context.Context, repo string) (*registrygate.Index, error) {
+	var idx registrygate.Index
+	if _, err := c.get(ctx, c.Endpoint+registrygate.IndexPathPrefix+repo, &idx); err != nil {
+		return nil, err
+	}
+	return &idx, nil
+}
+
+// Delete deletes one manifest. A manifest already gone counts as deleted.
+func (c *Client) Delete(ctx context.Context, repo, digest string) error {
+	req, err := http.NewRequestWithContext(ctx, http.MethodDelete, c.Endpoint+"/v2/"+repo+"/manifests/"+digest, nil)
+	if err != nil {
+		return err
+	}
+	req.SetBasicAuth(registrygate.PrincipalPrune, c.Token)
+	resp, err := c.http().Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	switch resp.StatusCode {
+	case http.StatusAccepted, http.StatusOK, http.StatusNotFound:
+		return nil
+	}
+	b, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
+	return fmt.Errorf("registry answered %s: %s", resp.Status, strings.TrimSpace(string(b)))
+}
+
+func (c *Client) get(ctx context.Context, u string, into any) (*http.Response, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := c.http().Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		b, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
+		return nil, fmt.Errorf("GET %s: registry answered %s: %s", u, resp.Status, strings.TrimSpace(string(b)))
+	}
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 64<<20)).Decode(into); err != nil {
+		return nil, fmt.Errorf("GET %s: %w", u, err)
+	}
+	return resp, nil
+}

internal/registryprune/prune.go

@@ -0,0 +1,274 @@
+// Package registryprune deletes the manifests in the platform registry that
+// nothing uses any more, so the registry-gc sidecar's next sweep can free their
+// layers. Without it the registry only grows: every rebuild of a tag leaves the
+// previous manifest behind, a whitelist entry an admin removes keeps its image,
+// and each installer run adds a platform image.
+//
+// A manifest is kept when any of these hold:
+//
+//   - an image reference the platform still depends on names it: a whitelist
+//     entry (by tag, by wildcard tag, or by digest), a server's spec (servers are
+//     pinned by digest, so a sleeping server keeps the exact build it was created
+//     with even after its tag moved on), or the images the control plane and the
+//     build Jobs run;
+//   - it was pushed less than Grace ago, which covers a build that pushed but has
+//     not been admitted to the whitelist yet;
+//   - it lives under a platform-reserved root (felis/, mirror/), is tagged, and is
+//     among the KeepTagged most recently pushed tagged manifests of its
+//     repository. The installer owns those tags; the newest few stay for a
+//     rollback, the older ones go.
+//
+// Everything else is deleted through the registry gate as the prune principal,
+// which may do nothing but delete a manifest by digest.
+package registryprune
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"sort"
+	"strings"
+	"time"
+
+	"felis.lolicon.best/internal/registrygate"
+)
+
+// Defaults for Pruner's zero fields.
+const (
+	DefaultGrace      = 24 * time.Hour
+	DefaultKeepTagged = 5
+)
+
+// Registry is the pruner's view of the registry (Client in production).
+type Registry interface {
+	Repositories(ctx context.Context) ([]string, error)
+	Index(ctx context.Context, repo string) (*registrygate.Index, error)
+	Delete(ctx context.Context, repo, digest string) error
+}
+
+// Pruner decides and deletes.
+type Pruner struct {
+	Registry Registry
+	// Host is the registry host[:port] image refs spell (registry.felis.svc:5000).
+	// Refs under any other host are not this registry's and are ignored.
+	Host string
+	// Refs lists every image reference still in use. An error aborts the run: a
+	// partial view could delete an image something depends on.
+	Refs func(ctx context.Context) ([]string, error)
+	// Grace keeps manifests pushed this recently. Zero means DefaultGrace.
+	Grace time.Duration
+	// KeepTagged is how many tagged manifests per reserved repository survive by
+	// recency alone. Zero means DefaultKeepTagged.
+	KeepTagged int
+	// Now is the clock; nil means time.Now.
+	Now func() time.Time
+	// Log receives one line per deletion and a summary. Nil discards.
+	Log *slog.Logger
+}
+
+// Target is one manifest the pruner deletes.
+type Target struct {
+	Repo, Digest string
+}
+
+func (t Target) String() string { return t.Repo + "@" + t.Digest }
+
+// Report summarizes one run.
+type Report struct {
+	Repositories int
+	Manifests    int
+	Deleted      []Target
+	// Failed counts deletions the registry refused; they are retried next run.
+	Failed int
+}
+
+// Run lists the registry, decides, and deletes.
+func (p *Pruner) Run(ctx context.Context) (Report, error) {
+	var rep Report
+	if p.Registry == nil || p.Refs == nil || p.Host == "" {
+		return rep, errors.New("registryprune: Registry, Refs and Host are required")
+	}
+	refs, err := p.Refs(ctx)
+	if err != nil {
+		return rep, fmt.Errorf("registryprune: list image references: %w", err)
+	}
+	repos, err := p.Registry.Repositories(ctx)
+	if err != nil {
+		return rep, fmt.Errorf("registryprune: list repositories: %w", err)
+	}
+	indexes := make(map[string]*registrygate.Index, len(repos))
+	for _, repo := range repos {
+		idx, err := p.Registry.Index(ctx, repo)
+		if err != nil {
+			return rep, fmt.Errorf("registryprune: index %s: %w", repo, err)
+		}
+		indexes[repo] = idx
+		rep.Manifests += len(idx.Revisions)
+	}
+	rep.Repositories = len(repos)
+
+	now := time.Now
+	if p.Now != nil {
+		now = p.Now
+	}
+	for _, t := range Plan(indexes, refs, p.Host, now(), p.grace(), p.keepTagged()) {
+		if err := p.Registry.Delete(ctx, t.Repo, t.Digest); err != nil {
+			rep.Failed++
+			p.log().Warn("registry prune: delete failed", "manifest", t.String(), "err", err)
+			continue
+		}
+		rep.Deleted = append(rep.Deleted, t)
+		p.log().Info("registry prune: deleted manifest", "manifest", t.String())
+	}
+	return rep, nil
+}
+
+// Loop runs Run every interval until ctx ends, starting after one interval's
+// tenth so a restart loop does not hammer the registry.
+func (p *Pruner) Loop(ctx context.Context, every time.Duration) {
+	t := time.NewTimer(every / 10)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+		}
+		rep, err := p.Run(ctx)
+		if err != nil {
+			p.log().Error("registry prune failed", "err", err)
+		} else {
+			p.log().Info("registry prune finished", "repositories", rep.Repositories,
+				"manifests", rep.Manifests, "deleted", len(rep.Deleted), "failed", rep.Failed)
+		}
+		t.Reset(every)
+	}
+}
+
+func (p *Pruner) grace() time.Duration {
+	if p.Grace > 0 {
+		return p.Grace
+	}
+	return DefaultGrace
+}
+
+func (p *Pruner) keepTagged() int {
+	if p.KeepTagged > 0 {
+		return p.KeepTagged
+	}
+	return DefaultKeepTagged
+}
+
+func (p *Pruner) log() *slog.Logger {
+	if p.Log != nil {
+		return p.Log
+	}
+	return slog.New(slog.DiscardHandler)
+}
+
+// Plan decides which manifests to delete. It is pure so every keep rule is
+// tested without a registry.
+func Plan(indexes map[string]*registrygate.Index, refs []string, host string, now time.Time, grace time.Duration, keepTagged int) []Target {
+	keep := map[Target]bool{}
+	for _, ref := range refs {
+		repo, tag, digest, ok := parseRef(ref, host)
+		if !ok {
+			continue
+		}
+		idx := indexes[repo]
+		switch {
+		case digest != "":
+			keep[Target{repo, digest}] = true
+		case idx == nil:
+		case tag == "*":
+			for _, d := range idx.Tags {
+				keep[Target{repo, d}] = true
+			}
+		default:
+			if d, ok := idx.Tags[tag]; ok {
+				keep[Target{repo, d}] = true
+			}
+		}
+	}
+
+	repos := make([]string, 0, len(indexes))
+	for repo := range indexes {
+		repos = append(repos, repo)
+	}
+	sort.Strings(repos)
+
+	var out []Target
+	for _, repo := range repos {
+		idx := indexes[repo]
+		pushed := make(map[string]time.Time, len(idx.Revisions))
+		for _, r := range idx.Revisions {
+			pushed[r.Digest] = r.Pushed
+		}
+		if reserved(repo) {
+			for _, d := range newestTagged(idx, pushed, keepTagged) {
+				keep[Target{repo, d}] = true
+			}
+		}
+		for _, r := range idx.Revisions {
+			t := Target{repo, r.Digest}
+			if keep[t] || now.Sub(r.Pushed) < grace {
+				continue
+			}
+			out = append(out, t)
+		}
+	}
+	return out
+}
+
+// newestTagged returns the n most recently pushed distinct digests any tag in idx
+// names.
+func newestTagged(idx *registrygate.Index, pushed map[string]time.Time, n int) []string {
+	seen := map[string]bool{}
+	var tagged []string
+	for _, d := range idx.Tags {
+		if !seen[d] {
+			seen[d] = true
+			tagged = append(tagged, d)
+		}
+	}
+	sort.Slice(tagged, func(i, j int) bool {
+		pi, pj := pushed[tagged[i]], pushed[tagged[j]]
+		if !pi.Equal(pj) {
+			return pi.After(pj)
+		}
+		return tagged[i] < tagged[j]
+	})
+	if len(tagged) > n {
+		tagged = tagged[:n]
+	}
+	return tagged
+}
+
+func reserved(repo string) bool {
+	root, _, _ := strings.Cut(repo, "/")
+	for _, r := range registrygate.ReservedRepoRoots {
+		if root == r {
+			return true
+		}
+	}
+	return false
+}
+
+// parseRef splits host/repo[:tag][@digest] for refs under host. A ref with
+// neither tag nor digest means :latest, as it does for every image client.
+func parseRef(ref, host string) (repo, tag, digest string, ok bool) {
+	rest, ok := strings.CutPrefix(strings.TrimSpace(ref), host+"/")
+	if !ok || rest == "" {
+		return "", "", "", false
+	}
+	name, digest, _ := strings.Cut(rest, "@")
+	repo, tag = name, ""
+	if colon := strings.LastIndex(name, ":"); colon > strings.LastIndex(name, "/") {
+		repo, tag = name[:colon], name[colon+1:]
+	}
+	if tag == "" && digest == "" {
+		tag = "latest"
+	}
+	return repo, tag, digest, repo != ""
+}

internal/registryprune/prune_test.go

@@ -0,0 +1,299 @@
+package registryprune
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"felis.lolicon.best/internal/registrygate"
+)
+
+const host = "registry.felis.svc:5000"
+
+var now = time.Date(2026, 9, 24, 12, 0, 0, 0, time.UTC)
+
+func dg(c string) string { return "sha256:" + strings.Repeat(c, 64) }
+
+func rev(c string, age time.Duration) registrygate.Revision {
+	return registrygate.Revision{Digest: dg(c), Pushed: now.Add(-age)}
+}
+
+const day = 24 * time.Hour
+
+func targets(ts []Target) []string {
+	out := make([]string, 0, len(ts))
+	for _, t := range ts {
+		out = append(out, t.Repo+"@"+t.Digest[7:8])
+	}
+	sort.Strings(out)
+	return out
+}
+
+func TestPlanKeepsWhatIsReferencedOrRecent(t *testing.T) {
+	indexes := map[string]*registrygate.Index{
+		// Rebuilt twice: a is untagged and pinned by a server, b untagged and
+		// unused, c is :latest and whitelisted.
+		"user-uploads/sub-1": {
+			Revisions: []registrygate.Revision{rev("a", 30*day), rev("b", 20*day), rev("c", 10*day)},
+			Tags:      map[string]string{"latest": dg("c")},
+		},
+		// Whitelist entry removed, no server: goes.
+		"user-uploads/sub-2": {
+			Revisions: []registrygate.Revision{rev("d", 5*day)},
+			Tags:      map[string]string{"latest": dg("d")},
+		},
+		// Pushed an hour ago, not admitted yet: the grace keeps it.
+		"user-uploads/sub-3": {
+			Revisions: []registrygate.Revision{rev("e", time.Hour)},
+			Tags:      map[string]string{"latest": dg("e")},
+		},
+		// A wildcard whitelist entry keeps every tag, not an untagged leftover.
+		"modpacks/pack": {
+			Revisions: []registrygate.Revision{rev("f", 9*day), rev("1", 8*day), rev("2", 7*day)},
+			Tags:      map[string]string{"1.0": dg("f"), "1.1": dg("1")},
+		},
+	}
+	refs := []string{
+		host + "/user-uploads/sub-1:latest",
+		host + "/user-uploads/sub-1:latest@" + dg("a"),
+		host + "/modpacks/pack:*",
+		"docker.io/library/nginx:latest",
+		"",
+	}
+	got := targets(Plan(indexes, refs, host, now, day, 5))
+	want := []string{"modpacks/pack@2", "user-uploads/sub-1@b", "user-uploads/sub-2@d"}
+	if fmt.Sprint(got) != fmt.Sprint(want) {
+		t.Fatalf("plan = %v, want %v", got, want)
+	}
+}
+
+func TestPlanKeepsTheNewestTaggedPlatformImages(t *testing.T) {
+	indexes := map[string]*registrygate.Index{
+		// Seven installer runs: b1..b7 tagged, plus untagged leftovers x (pinned by
+		// a server) and y.
+		"felis/felis": {
+			Revisions: []registrygate.Revision{
+				rev("1", 70*day), rev("2", 60*day), rev("3", 50*day), rev("4", 40*day),
+				rev("5", 30*day), rev("6", 20*day), rev("7", 10*day),
+				rev("x", 80*day), rev("y", 90*day),
+			},
+			Tags: map[string]string{
+				"b1": dg("1"), "b2": dg("2"), "b3": dg("3"), "b4": dg("4"),
+				"b5": dg("5"), "b6": dg("6"), "b7": dg("7"),
+			},
+		},
+		// The scanner DB mirror: one tag, kept however old.
+		"mirror/trivy-db": {
+			Revisions: []registrygate.Revision{rev("8", 200*day), rev("9", 300*day)},
+			Tags:      map[string]string{"2": dg("8")},
+		},
+	}
+	refs := []string{
+		// The running control plane is older than the newest three.
+		host + "/felis/felis:b2",
+		host + "/felis/felis:b5@" + dg("x"),
+	}
+	got := targets(Plan(indexes, refs, host, now, day, 3))
+	want := []string{"felis/felis@1", "felis/felis@3", "felis/felis@4", "felis/felis@y", "mirror/trivy-db@9"}
+	if fmt.Sprint(got) != fmt.Sprint(want) {
+		t.Fatalf("plan = %v, want %v", got, want)
+	}
+}
+
+func TestParseRef(t *testing.T) {
+	for _, c := range []struct {
+		ref, repo, tag, digest string
+		ok                     bool
+	}{
+		{host + "/felis/paper:demo", "felis/paper", "demo", "", true},
+		{host + "/felis/paper:demo@" + dg("a"), "felis/paper", "demo", dg("a"), true},
+		{host + "/felis/paper@" + dg("a"), "felis/paper", "", dg("a"), true},
+		{host + "/felis/paper", "felis/paper", "latest", "", true},
+		{host + "/pack:*", "pack", "*", "", true},
+		{"other:5000/felis/paper:demo", "", "", "", false},
+		{host + "/", "", "", "", false},
+	} {
+		repo, tag, digest, ok := parseRef(c.ref, host)
+		if repo != c.repo || tag != c.tag || digest != c.digest || ok != c.ok {
+			t.Errorf("parseRef(%q) = %q %q %q %v, want %q %q %q %v", c.ref, repo, tag, digest, ok, c.repo, c.tag, c.digest, c.ok)
+		}
+	}
+}
+
+// fakeRegistry serves _catalog (paged by one), the manifest index and DELETE.
+type fakeRegistry struct {
+	mu      sync.Mutex
+	indexes map[string]*registrygate.Index
+	deletes []string
+	auth    []string
+}
+
+func (f *fakeRegistry) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	switch {
+	case r.URL.Path == "/v2/_catalog":
+		var repos []string
+		for repo := range f.indexes {
+			repos = append(repos, repo)
+		}
+		sort.Strings(repos)
+		last := r.URL.Query().Get("last")
+		var page []string
+		for _, repo := range repos {
+			if repo > last {
+				page = append(page, repo)
+				break
+			}
+		}
+		if len(page) == 1 && page[0] != repos[len(repos)-1] {
+			w.Header().Set("Link", `</v2/_catalog?last=`+url.QueryEscape(page[0])+`&n=1>; rel="next"`)
+		}
+		_ = json.NewEncoder(w).Encode(map[string][]string{"repositories": page})
+	case strings.HasPrefix(r.URL.Path, registrygate.IndexPathPrefix):
+		idx := f.indexes[strings.TrimPrefix(r.URL.Path, registrygate.IndexPathPrefix)]
+		_ = json.NewEncoder(w).Encode(idx)
+	case r.Method == http.MethodDelete:
+		user, pass, _ := r.BasicAuth()
+		f.auth = append(f.auth, user+":"+pass)
+		f.deletes = append(f.deletes, r.URL.Path)
+		w.WriteHeader(http.StatusAccepted)
+	default:
+		http.NotFound(w, r)
+	}
+}
+
+func TestRunDeletesThroughTheGateAsThePrunePrincipal(t *testing.T) {
+	reg := &fakeRegistry{indexes: map[string]*registrygate.Index{
+		"e2e/probe":          {Revisions: []registrygate.Revision{rev("a", 3*day)}, Tags: map[string]string{"latest": dg("a")}},
+		"user-uploads/sub-1": {Revisions: []registrygate.Revision{rev("b", 3*day)}, Tags: map[string]string{"latest": dg("b")}},
+		"felis/paper":        {Revisions: []registrygate.Revision{rev("c", 3*day)}, Tags: map[string]string{"demo": dg("c")}},
+	}}
+	srv := httptest.NewServer(reg)
+	t.Cleanup(srv.Close)
+	p := &Pruner{
+		Registry: &Client{Endpoint: srv.URL, Token: "prune-secret"},
+		Host:     host,
+		Refs: func(context.Context) ([]string, error) {
+			return []string{host + "/user-uploads/sub-1:latest"}, nil
+		},
+		Now: func() time.Time { return now },
+	}
+	rep, err := p.Run(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rep.Repositories != 3 || rep.Manifests != 3 || len(rep.Deleted) != 1 || rep.Failed != 0 {
+		t.Fatalf("report = %+v, want 3 repos, 3 manifests, 1 deleted", rep)
+	}
+	if want := "/v2/e2e/probe/manifests/" + dg("a"); len(reg.deletes) != 1 || reg.deletes[0] != want {
+		t.Fatalf("deletes = %v, want [%s]", reg.deletes, want)
+	}
+	if reg.auth[0] != registrygate.PrincipalPrune+":prune-secret" {
+		t.Fatalf("delete sent as %q, want the prune principal", reg.auth[0])
+	}
+}
+
+func TestRunAbortsOnAPartialView(t *testing.T) {
+	reg := &fakeRegistry{indexes: map[string]*registrygate.Index{
+		"e2e/probe": {Revisions: []registrygate.Revision{rev("a", 3*day)}, Tags: map[string]string{"latest": dg("a")}},
+	}}
+	srv := httptest.NewServer(reg)
+	t.Cleanup(srv.Close)
+	p := &Pruner{
+		Registry: &Client{Endpoint: srv.URL, Token: "t"},
+		Host:     host,
+		Refs: func(context.Context) ([]string, error) {
+			return nil, errors.New("cluster unreachable")
+		},
+		Now: func() time.Time { return now },
+	}
+	if _, err := p.Run(context.Background()); err == nil {
+		t.Fatal("run with no view of the servers succeeded")
+	}
+	if len(reg.deletes) != 0 {
+		t.Fatalf("deleted %v without knowing what is in use", reg.deletes)
+	}
+}
+
+// Through the real gate: the index comes off the data directory, the delete is
+// authorized as the prune principal and reaches the registry without the
+// credential.
+func TestRunThroughTheGate(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "docker/registry/v2/repositories/e2e/probe/_manifests")
+	hex := strings.Repeat("a", 64)
+	for _, dir := range []string{"revisions/sha256/" + hex, "tags/latest/current"} {
+		if err := os.MkdirAll(filepath.Join(repoDir, dir), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, f := range []string{"revisions/sha256/" + hex + "/link", "tags/latest/current/link"} {
+		if err := os.WriteFile(filepath.Join(repoDir, f), []byte("sha256:"+hex), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	var mu sync.Mutex
+	var upstream []string
+	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		mu.Lock()
+		upstream = append(upstream, r.Method+" "+r.URL.Path+" auth="+r.Header.Get("Authorization"))
+		mu.Unlock()
+		switch {
+		case r.URL.Path == "/v2/_catalog":
+			_, _ = w.Write([]byte(`{"repositories":["e2e/probe"]}`))
+		case r.Method == http.MethodDelete:
+			w.WriteHeader(http.StatusAccepted)
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	t.Cleanup(up.Close)
+	target, _ := url.Parse(up.URL)
+	g := registrygate.New(target, map[string]string{
+		registrygate.PrincipalPrune: "prune-secret",
+		registrygate.PrincipalBuild: "build-secret",
+	}, nil)
+	g.DataDir = root
+	gate := httptest.NewServer(g)
+	t.Cleanup(gate.Close)
+
+	refs := func(context.Context) ([]string, error) { return nil, nil }
+	later := func() time.Time { return time.Now().Add(48 * time.Hour) }
+
+	// The build principal's token is not good for a delete.
+	wrong := &Pruner{Registry: &Client{Endpoint: gate.URL, Token: "build-secret"}, Host: host, Refs: refs, Now: later}
+	if rep, err := wrong.Run(context.Background()); err != nil || rep.Failed != 1 || len(rep.Deleted) != 0 {
+		t.Fatalf("run with the wrong token = %+v, %v; want one refused delete", rep, err)
+	}
+
+	p := &Pruner{Registry: &Client{Endpoint: gate.URL, Token: "prune-secret"}, Host: host, Refs: refs, Now: later}
+	rep, err := p.Run(context.Background())
+	if err != nil || len(rep.Deleted) != 1 || rep.Failed != 0 {
+		t.Fatalf("run = %+v, %v; want one deletion", rep, err)
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	want := "DELETE /v2/e2e/probe/manifests/sha256:" + hex + " auth="
+	var deletes []string
+	for _, u := range upstream {
+		if strings.HasPrefix(u, "DELETE") {
+			deletes = append(deletes, u)
+		}
+	}
+	if len(deletes) != 1 || deletes[0] != want {
+		t.Fatalf("upstream deletes = %q, want [%q]", deletes, want)
+	}
+}