feat(admin): online dictionary update — upload archive, preview word diff, install & activate

Replace the dictionary hot-reload with an online update flow in the GM console
(/_gm/dictionary): the operator uploads scrabble-dawg-vX.Y.Z.tar.gz, previews the
per-variant words added/removed against the active dictionary, and confirms to
install + activate it. Versions are immutable; in-progress games keep their pinned
version while new games use the new one.

- engine: DiffWords (enumerate both DAWGs, decode only the differences), OpenFinder,
  Registry.Finder, DictFiles; OpenWithVersions skips the .staging area.
- dictadmin: hardened release-archive validation + extraction (path-traversal,
  symlink, oversize, entry-count rejection) and staging -> install (atomic rename).
- game: active dictionary version persisted in the dictionary_state singleton
  (single source of truth, restored on boot), concurrency-safe accessor.
- storage: BACKEND_DICT_DIR is a named volume seeded from the image (nonroot-owned),
  so uploaded versions persist across redeploys; the build's DICT_VERSION labels the
  seed and equals the resident tag (BACKEND_DICT_VERSION).
- docs: ARCHITECTURE §5, FUNCTIONAL (+ru), backend README, TESTING, PRERELEASE.

Tests: engine + dictadmin unit; integration upload->preview->install->activate->
restart->pin->immutability->CSRF.

backend/Dockerfile

@@ -37,7 +37,17 @@ RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -o /out/backend ./backend/cmd/ba
 
 # --- runtime -----------------------------------------------------------------
 FROM gcr.io/distroless/static-debian12:nonroot
+# Re-declare the build arg in this stage so it labels the seed dictionary. One
+# DICT_VERSION drives both the artifact the dawg stage downloads and the version
+# label the binary pins, so the resident version equals the release tag.
+ARG DICT_VERSION=v1.0.0
 COPY --from=build /out/backend /usr/local/bin/backend
-COPY --from=dawg /dawg /opt/dawg
+# Own the seed dictionary as the nonroot runtime user (UID 65532): a named volume
+# mounted at /opt/dawg inherits this ownership on first use, so the admin console
+# can write new version subdirectories at runtime. The volume preserves uploaded
+# versions across deploys and, once seeded, is not re-seeded — so after bootstrap
+# every dictionary change goes through the console, not a rebuild (ARCHITECTURE.md §5).
+COPY --from=dawg --chown=65532:65532 /dawg /opt/dawg
 ENV BACKEND_DICT_DIR=/opt/dawg
+ENV BACKEND_DICT_VERSION=${DICT_VERSION}
 ENTRYPOINT ["/usr/local/bin/backend"]

backend/README.md

@@ -81,8 +81,10 @@ with no identity, excluded from statistics. The server-rendered
 the gateway fronts it with Basic-Auth and a same-origin guard protects its POSTs), the
 **complaint resolution** lifecycle (the `complaints` `disposition`/`resolution_note`/
 `resolved_at`/`applied_in_version` columns + the `status` CHECK) feeding a dictionary-change
-pipeline, dictionary **hot-reload** from `BACKEND_DICT_DIR/<version>/`
-(`engine.OpenWithVersions` / `Registry.LoadAvailable`), and operator **broadcasts** via a
+pipeline, the online **dictionary update** (upload the `scrabble-dawg-vX.Y.Z.tar.gz` release
+archive, preview the per-variant word diff, then install + activate — `internal/dictadmin` +
+`engine.DiffWords` / `Registry.LoadAvailable`, written to per-version subdirectories of the
+`BACKEND_DICT_DIR` volume with the active version persisted in `dictionary_state`), and operator **broadcasts** via a
 backend Telegram-connector client (`internal/connector`, `BACKEND_CONNECTOR_ADDR`) — each
 broadcast picks the delivering bot by an operator-chosen language. `accounts.service_language`
 holds the language tag of the bot a Telegram

backend/cmd/backend/main.go

@@ -135,6 +135,14 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	accounts := account.NewStore(db)
 	accounts.SetMetrics(tel.MeterProvider().Meter("scrabble/backend/account"))
 	games := game.NewService(game.NewStore(db), accounts, registry, cfg.Game, logger)
+	// Reconcile the persisted active dictionary version with the registry: a
+	// version activated through the admin console (and written to the dictionary
+	// volume) is adopted again after a restart; otherwise the configured seed
+	// version is kept and persisted (docs/ARCHITECTURE.md §5).
+	if err := games.InitActiveVersion(ctx); err != nil {
+		return fmt.Errorf("init active dictionary version: %w", err)
+	}
+	logger.Info("active dictionary version", zap.String("version", games.ActiveVersion()))
 	games.SetNotifier(hub)
 	games.SetMetrics(tel.MeterProvider().Meter("scrabble/backend/game"))
 	go games.RunSweeper(ctx, cfg.Game.TimeoutSweepInterval)

backend/internal/adminconsole/render_test.go

@@ -36,7 +36,8 @@ func TestRendererRendersEveryPage(t *testing.T) {
 		{"complaints", ComplaintsView{Items: []ComplaintRow{{ID: "c1", Word: "qi", Status: "open"}}, Status: "open", Pager: NewPager(1, 50, 1)}, "qi"},
 		{"messages", MessagesView{Items: []MessageRow{{ID: "m1", SenderID: "a1", SenderName: "Kaya", Source: "telegram", Body: "good luck", GameID: "g1"}}, Pager: NewPager(1, 50, 1)}, "good luck"},
 		{"complaint_detail", ComplaintDetailView{ID: "c1", Word: "qi", Variant: "scrabble_en"}, "Resolve"},
-		{"dictionary", DictionaryView{Variants: []VariantVersions{{Variant: "scrabble_en", Latest: "v1", Versions: []string{"v1"}}}, Changes: []DictChangeRow{{Variant: "scrabble_en", Word: "qi", Action: "add"}}}, "Hot-reload"},
+		{"dictionary", DictionaryView{ActiveVersion: "v1.0.0", Variants: []VariantVersions{{Variant: "scrabble_en", Versions: []string{"v1.0.0"}}}, Changes: []DictChangeRow{{Variant: "scrabble_en", Word: "qi", Action: "add"}}}, "Update dictionaries"},
+		{"dictionary_preview", DictionaryPreviewView{Version: "v1.1.0", Token: "0123456789abcdef0123456789abcdef", ActiveVersion: "v1.0.0", Variants: []VariantDiffRow{{Variant: "scrabble_en", AddedCount: 2, RemovedCount: 1, AddedSample: []string{"qi", "za"}, RemovedSample: []string{"xqz"}, RemovedTruncated: true}}}, "v1.1.0"},
 		{"broadcast", BroadcastView{ConnectorEnabled: true}, "Post to the game channel"},
 		{"message", MessageView{Heading: "Done", Body: "ok", Back: "/_gm/"}, "Done"},
 	}

backend/internal/adminconsole/templates/pages/dictionary.gohtml

@@ -1,21 +1,24 @@
 {{define "content" -}}
 <h1>Dictionary</h1>
 {{with .Data}}
+<section class="panel"><h2>Active version</h2>
+<p>New games pin <span class="pill">{{.ActiveVersion}}</span>. Games already in progress keep the version they started on.</p>
+</section>
 <section class="panel"><h2>Resident versions</h2>
 <table class="list">
-<thead><tr><th>Variant</th><th>Latest</th><th>Resident</th></tr></thead>
+<thead><tr><th>Variant</th><th>Resident</th></tr></thead>
 <tbody>
 {{range .Variants}}
-<tr><td>{{.Variant}}</td><td>{{.Latest}}</td><td>{{range .Versions}}<span class="pill">{{.}}</span> {{end}}</td></tr>
+<tr><td>{{.Variant}}</td><td>{{range .Versions}}<span class="pill">{{.}}</span> {{end}}</td></tr>
 {{end}}
 </tbody>
 </table>
 </section>
-<section class="panel"><h2>Hot-reload a version</h2>
-<p class="note">Drop the rebuilt DAWG set into BACKEND_DICT_DIR/&lt;version&gt;/ first, then load it here.</p>
-<form class="form" method="post" action="/_gm/dictionary/reload">
-<label>Version <input type="text" name="version" placeholder="v2" required></label>
-<div><button type="submit">Reload</button></div>
+<section class="panel"><h2>Update dictionaries</h2>
+<p class="note">Upload the release archive <code>scrabble-dawg-vX.Y.Z.tar.gz</code> downloaded from the scrabble-dictionary repository. The next step previews the added and removed words per variant; nothing is installed until you confirm.</p>
+<form class="form" method="post" action="/_gm/dictionary/upload" enctype="multipart/form-data">
+<label>Release archive <input type="file" name="archive" accept=".gz,.tgz,application/gzip" required></label>
+<div><button type="submit">Upload &amp; preview</button></div>
 </form>
 </section>
 <section class="panel"><h2>Pending dictionary changes</h2>
@@ -35,7 +38,7 @@
 <option value="erudit_ru">erudit_ru</option>
 </select>
 </label>
-<label>In version <input type="text" name="version" placeholder="v2" required></label>
+<label>In version <input type="text" name="version" value="{{.ActiveVersion}}" required></label>
 <div><button type="submit">Mark applied</button></div>
 </form>
 </section>

backend/internal/adminconsole/templates/pages/dictionary_preview.gohtml

@@ -0,0 +1,27 @@
+{{define "content" -}}
+<h1>Dictionary update — preview</h1>
+{{with .Data}}
+<section class="panel">
+<p>Comparing the uploaded archive against the active version <span class="pill">{{.ActiveVersion}}</span>. Review the changes below, then confirm to install and activate.</p>
+<form class="form" method="post" action="/_gm/dictionary/install">
+<input type="hidden" name="token" value="{{.Token}}">
+<label>Version <input type="text" name="version" value="{{.Version}}" required></label>
+<div><button type="submit">Update dictionaries</button></div>
+</form>
+</section>
+{{range .Variants}}
+<section class="panel">
+<h2>{{.Variant}}</h2>
+<p><strong>{{.AddedCount}}</strong> added, <strong>{{.RemovedCount}}</strong> removed.
+{{if .LargeRemoval}}<span class="warn">Large removal — double-check this is expected before updating.</span>{{end}}</p>
+<h3>Added{{if .AddedTruncated}} (showing first {{len .AddedSample}}){{end}}</h3>
+<p>{{range .AddedSample}}<code>{{.}}</code> {{else}}<span class="note">none</span>{{end}}</p>
+{{if .AddedTruncated}}<p class="note">… and more; the full list is not shown.</p>{{end}}
+<h3>Removed{{if .RemovedTruncated}} (showing first {{len .RemovedSample}}){{end}}</h3>
+<p>{{range .RemovedSample}}<code>{{.}}</code> {{else}}<span class="note">none</span>{{end}}</p>
+{{if .RemovedTruncated}}<p class="note">… and more; the full list is not shown.</p>{{end}}
+</section>
+{{end}}
+<p><a href="/_gm/dictionary">Cancel</a></p>
+{{end}}
+{{- end}}

backend/internal/adminconsole/views.go

@@ -43,7 +43,10 @@ type DashboardView struct {
 	ActiveGames    int
 	OpenComplaints int
 	PendingChanges int
-	Variants       []VariantVersions
+	// ActiveVersion is the dictionary version new games pin (the persisted active
+	// version), distinct from the per-variant resident versions.
+	ActiveVersion string
+	Variants      []VariantVersions
 }
 
 // UsersView is the paginated account list.
@@ -237,11 +240,13 @@ type ComplaintDetailView struct {
 	Resolved       bool
 }
 
-// DictionaryView lists the resident versions per variant and the pending
-// wordlist changes from accepted complaints.
+// DictionaryView lists the resident versions per variant, the active version new
+// games pin, and the pending wordlist changes from accepted complaints.
 type DictionaryView struct {
-	Variants []VariantVersions
-	Changes  []DictChangeRow
+	// ActiveVersion is the dictionary version new games pin; the update form sets it.
+	ActiveVersion string
+	Variants      []VariantVersions
+	Changes       []DictChangeRow
 }
 
 // DictChangeRow is one pending wordlist edit.
@@ -252,6 +257,32 @@ type DictChangeRow struct {
 	ResolvedAt string
 }
 
+// DictionaryPreviewView is the second step of a dictionary update: the version
+// parsed from the uploaded archive (editable before confirming), the staging token
+// that names the uploaded files on disk, the active version the diff is against, and
+// the per-variant word diff.
+type DictionaryPreviewView struct {
+	Version       string
+	Token         string
+	ActiveVersion string
+	Variants      []VariantDiffRow
+}
+
+// VariantDiffRow summarises one variant's word diff in the update preview.
+// AddedCount/RemovedCount are the full totals; AddedSample/RemovedSample are the
+// first words shown (capped); AddedTruncated/RemovedTruncated mark a capped list;
+// LargeRemoval flags a removal large enough to warrant caution before confirming.
+type VariantDiffRow struct {
+	Variant          string
+	AddedCount       int
+	RemovedCount     int
+	AddedSample      []string
+	RemovedSample    []string
+	AddedTruncated   bool
+	RemovedTruncated bool
+	LargeRemoval     bool
+}
+
 // BroadcastView is the operator-broadcast form page.
 type BroadcastView struct {
 	ConnectorEnabled bool

backend/internal/dictadmin/dictadmin.go

@@ -0,0 +1,262 @@
+// Package dictadmin stages and installs scrabble-dictionary release archives for
+// the admin console's online dictionary-update flow. It validates the release
+// archive (scrabble-dawg-vX.Y.Z.tar.gz), extracts it safely into a per-version
+// directory under BACKEND_DICT_DIR, and keeps a staging area for the two-step
+// upload-then-confirm interaction. Extraction is hardened against the usual
+// archive risks (path traversal, symlinks, decompression bombs).
+package dictadmin
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	crand "crypto/rand"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp"
+	"time"
+
+	"scrabble/backend/internal/engine"
+)
+
+// MaxArchiveBytes bounds an uploaded release archive; the handler wraps the request
+// body in an http.MaxBytesReader with this limit. The three compressed DAWGs are a
+// few MB together, so 64 MiB is generous.
+const MaxArchiveBytes int64 = 64 << 20
+
+// stagingRoot is the dot-prefixed directory under the dictionary dir holding
+// not-yet-installed uploads. The engine's boot scan skips dot-prefixed dirs, so a
+// staged upload never becomes a resident version.
+const stagingRoot = ".staging"
+
+// stagingTTL is how long an abandoned staged upload lingers before Stage sweeps it.
+const stagingTTL = time.Hour
+
+// maxMemberBytes and maxEntries bound a single archive member and the number of
+// entries, defeating decompression and entry-count bombs. They are variables so
+// tests can lower them. maxMemberBytes is per file; a real DAWG is a few MB.
+var (
+	maxMemberBytes int64 = 32 << 20
+	maxEntries           = 64
+)
+
+var (
+	nameRE    = regexp.MustCompile(`^scrabble-dawg-(v[0-9]+\.[0-9]+\.[0-9]+)\.tar\.gz$`)
+	versionRE = regexp.MustCompile(`^v[0-9]+\.[0-9]+\.[0-9]+$`)
+	tokenRE   = regexp.MustCompile(`^[0-9a-f]{32}$`)
+)
+
+// ParseVersionFromName extracts the version from a release archive filename of the
+// form scrabble-dawg-vX.Y.Z.tar.gz, or returns an error for any other shape.
+func ParseVersionFromName(filename string) (string, error) {
+	m := nameRE.FindStringSubmatch(filename)
+	if m == nil {
+		return "", fmt.Errorf("dictadmin: %q is not a scrabble-dawg-vX.Y.Z.tar.gz archive", filename)
+	}
+	return m[1], nil
+}
+
+// ValidVersion reports whether v is a vMAJOR.MINOR.PATCH version label. It guards
+// the operator's manual override before the version is used as a directory name.
+func ValidVersion(v string) bool {
+	return versionRE.MatchString(v)
+}
+
+// Extract reads a gzip+tar release archive from r and writes the recognised
+// dictionary files into destDir, returning the variants found in catalogue order.
+// Only regular files whose base name is a known DAWG filename are written (their
+// directory part is discarded, so a traversal entry cannot escape destDir);
+// symlinks and other types are ignored, and oversize members or an excessive entry
+// count are rejected.
+func Extract(r io.Reader, destDir string) ([]engine.Variant, error) {
+	gz, err := gzip.NewReader(r)
+	if err != nil {
+		return nil, fmt.Errorf("dictadmin: open gzip: %w", err)
+	}
+	defer func() { _ = gz.Close() }()
+	tr := tar.NewReader(gz)
+
+	byName := filenameToVariant()
+	seen := make(map[engine.Variant]bool)
+	entries := 0
+	for {
+		hdr, err := tr.Next()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			return nil, fmt.Errorf("dictadmin: read archive: %w", err)
+		}
+		entries++
+		if entries > maxEntries {
+			return nil, fmt.Errorf("dictadmin: archive has more than %d entries", maxEntries)
+		}
+		if hdr.Typeflag != tar.TypeReg {
+			continue
+		}
+		base := filepath.Base(filepath.Clean(hdr.Name))
+		v, ok := byName[base]
+		if !ok {
+			continue
+		}
+		if seen[v] {
+			return nil, fmt.Errorf("dictadmin: duplicate %s in archive", base)
+		}
+		if hdr.Size > maxMemberBytes {
+			return nil, fmt.Errorf("dictadmin: %s exceeds the %d-byte member limit", base, maxMemberBytes)
+		}
+		if err := writeMember(filepath.Join(destDir, base), tr); err != nil {
+			return nil, err
+		}
+		seen[v] = true
+	}
+
+	var found []engine.Variant
+	for _, v := range engine.Variants() {
+		if seen[v] {
+			found = append(found, v)
+		}
+	}
+	return found, nil
+}
+
+// writeMember copies one archive member into path, bounding it at maxMemberBytes so
+// a member whose declared size lies cannot exhaust the disk.
+func writeMember(path string, tr *tar.Reader) error {
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o644)
+	if err != nil {
+		return fmt.Errorf("dictadmin: create %s: %w", filepath.Base(path), err)
+	}
+	defer func() { _ = f.Close() }()
+	n, err := io.Copy(f, io.LimitReader(tr, maxMemberBytes+1))
+	if err != nil {
+		return fmt.Errorf("dictadmin: write %s: %w", filepath.Base(path), err)
+	}
+	if n > maxMemberBytes {
+		return fmt.Errorf("dictadmin: %s exceeds the %d-byte member limit", filepath.Base(path), maxMemberBytes)
+	}
+	return nil
+}
+
+// filenameToVariant inverts the engine's variant-to-filename map.
+func filenameToVariant() map[string]engine.Variant {
+	files := engine.DictFiles()
+	out := make(map[string]engine.Variant, len(files))
+	for v, name := range files {
+		out[name] = v
+	}
+	return out
+}
+
+// Manager stages and installs release archives under a dictionary directory
+// (BACKEND_DICT_DIR).
+type Manager struct {
+	dir string
+}
+
+// New constructs a Manager rooted at the dictionary directory dir.
+func New(dir string) *Manager {
+	return &Manager{dir: dir}
+}
+
+// Stage accepts an uploaded archive: it sweeps abandoned previews, allocates a
+// staging directory under <dir>/.staging/<token>, extracts the archive there and
+// returns the token and the variants found. The staging directory is removed on an
+// extraction error.
+func (m *Manager) Stage(r io.Reader) (string, []engine.Variant, error) {
+	m.cleanStaging()
+	token, err := newToken()
+	if err != nil {
+		return "", nil, err
+	}
+	dest := filepath.Join(m.dir, stagingRoot, token)
+	if err := os.MkdirAll(dest, 0o755); err != nil {
+		return "", nil, fmt.Errorf("dictadmin: create staging dir: %w", err)
+	}
+	variants, err := Extract(r, dest)
+	if err != nil {
+		_ = os.RemoveAll(dest)
+		return "", nil, err
+	}
+	return token, variants, nil
+}
+
+// StagedDir returns the directory of the staged upload named by token, after
+// validating the token's shape and confirming the directory exists.
+func (m *Manager) StagedDir(token string) (string, error) {
+	if !tokenRE.MatchString(token) {
+		return "", fmt.Errorf("dictadmin: invalid staging token")
+	}
+	dir := filepath.Join(m.dir, stagingRoot, token)
+	info, err := os.Stat(dir)
+	if err != nil || !info.IsDir() {
+		return "", fmt.Errorf("dictadmin: staged upload not found")
+	}
+	return dir, nil
+}
+
+// VersionExists reports whether the version directory <dir>/<version> is present.
+func (m *Manager) VersionExists(version string) bool {
+	info, err := os.Stat(filepath.Join(m.dir, version))
+	return err == nil && info.IsDir()
+}
+
+// Install promotes a staged upload into its version directory <dir>/<version> by an
+// atomic rename (same filesystem) and returns the destination path. It rejects an
+// invalid version and refuses to overwrite an existing version: versions are
+// immutable, protecting games pinned to that tag.
+func (m *Manager) Install(token, version string) (string, error) {
+	if !ValidVersion(version) {
+		return "", fmt.Errorf("dictadmin: invalid version %q", version)
+	}
+	staged, err := m.StagedDir(token)
+	if err != nil {
+		return "", err
+	}
+	if m.VersionExists(version) {
+		return "", fmt.Errorf("dictadmin: version %s already exists", version)
+	}
+	dest := filepath.Join(m.dir, version)
+	if err := os.Rename(staged, dest); err != nil {
+		return "", fmt.Errorf("dictadmin: install %s: %w", version, err)
+	}
+	return dest, nil
+}
+
+// Discard removes the staging directory named by token, best effort. It is called
+// when a preview is rejected (an incomplete or unusable archive).
+func (m *Manager) Discard(token string) {
+	if dir, err := m.StagedDir(token); err == nil {
+		_ = os.RemoveAll(dir)
+	}
+}
+
+// cleanStaging removes staging directories older than stagingTTL, best effort.
+func (m *Manager) cleanStaging() {
+	root := filepath.Join(m.dir, stagingRoot)
+	entries, err := os.ReadDir(root)
+	if err != nil {
+		return
+	}
+	cutoff := time.Now().Add(-stagingTTL)
+	for _, e := range entries {
+		if !e.IsDir() {
+			continue
+		}
+		if info, err := e.Info(); err == nil && info.ModTime().Before(cutoff) {
+			_ = os.RemoveAll(filepath.Join(root, e.Name()))
+		}
+	}
+}
+
+// newToken returns a 32-hex-character random staging token.
+func newToken() (string, error) {
+	var b [16]byte
+	if _, err := crand.Read(b[:]); err != nil {
+		return "", fmt.Errorf("dictadmin: generate token: %w", err)
+	}
+	return hex.EncodeToString(b[:]), nil
+}

backend/internal/dictadmin/dictadmin_test.go

@@ -0,0 +1,248 @@
+package dictadmin
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"scrabble/backend/internal/engine"
+)
+
+// dawgNames are the three committed dictionary filenames a release archive holds.
+func dawgNames() []string {
+	out := make([]string, 0, 3)
+	for _, name := range engine.DictFiles() {
+		out = append(out, name)
+	}
+	return out
+}
+
+// fullArchive builds a gzip+tar archive holding all three dictionary files with
+// dummy content, the shape of a real release archive.
+func fullArchive(t *testing.T) []byte {
+	t.Helper()
+	files := map[string][]byte{}
+	for _, n := range dawgNames() {
+		files[n] = []byte("dawg:" + n)
+	}
+	return tarGz(t, files, nil)
+}
+
+// tarGz builds a gzip+tar archive. regular maps a member name to its bytes; extra
+// lets a test inject crafted headers (symlinks, oversized members, junk entries).
+func tarGz(t *testing.T, regular map[string][]byte, extra []*tar.Header) []byte {
+	t.Helper()
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gz)
+	for name, data := range regular {
+		if err := tw.WriteHeader(&tar.Header{Name: name, Mode: 0o644, Size: int64(len(data)), Typeflag: tar.TypeReg}); err != nil {
+			t.Fatalf("write header %s: %v", name, err)
+		}
+		if _, err := tw.Write(data); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+	}
+	for _, hdr := range extra {
+		if err := tw.WriteHeader(hdr); err != nil {
+			t.Fatalf("write extra header %s: %v", hdr.Name, err)
+		}
+		if hdr.Typeflag == tar.TypeReg && hdr.Size > 0 {
+			if _, err := tw.Write(bytes.Repeat([]byte("x"), int(hdr.Size))); err != nil {
+				t.Fatalf("write extra %s: %v", hdr.Name, err)
+			}
+		}
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("close tar: %v", err)
+	}
+	if err := gz.Close(); err != nil {
+		t.Fatalf("close gzip: %v", err)
+	}
+	return buf.Bytes()
+}
+
+func TestParseVersionFromName(t *testing.T) {
+	cases := []struct {
+		name    string
+		want    string
+		wantErr bool
+	}{
+		{"scrabble-dawg-v1.2.3.tar.gz", "v1.2.3", false},
+		{"scrabble-dawg-v10.0.1.tar.gz", "v10.0.1", false},
+		{"scrabble-dawg-v1.2.tar.gz", "", true},
+		{"scrabble-dawg-1.2.3.tar.gz", "", true},
+		{"scrabble-dawg-v1.2.3.zip", "", true},
+		{"dawg-v1.2.3.tar.gz", "", true},
+		{"scrabble-dawg-v1.2.3.tar.gz.exe", "", true},
+		{"", "", true},
+	}
+	for _, c := range cases {
+		got, err := ParseVersionFromName(c.name)
+		if c.wantErr {
+			if err == nil {
+				t.Errorf("ParseVersionFromName(%q) = %q, want error", c.name, got)
+			}
+			continue
+		}
+		if err != nil || got != c.want {
+			t.Errorf("ParseVersionFromName(%q) = %q, %v; want %q", c.name, got, err, c.want)
+		}
+	}
+}
+
+func TestValidVersion(t *testing.T) {
+	valid := []string{"v1.0.0", "v10.20.30", "v0.0.1"}
+	invalid := []string{"v1.0", "1.0.0", "v1.0.0.0", "v1.0.0/..", "v1.0.0 ", "", "vx.y.z", "../v1.0.0"}
+	for _, v := range valid {
+		if !ValidVersion(v) {
+			t.Errorf("ValidVersion(%q) = false, want true", v)
+		}
+	}
+	for _, v := range invalid {
+		if ValidVersion(v) {
+			t.Errorf("ValidVersion(%q) = true, want false", v)
+		}
+	}
+}
+
+func TestExtractAcceptsFullArchive(t *testing.T) {
+	dir := t.TempDir()
+	variants, err := Extract(bytes.NewReader(fullArchive(t)), dir)
+	if err != nil {
+		t.Fatalf("Extract: %v", err)
+	}
+	if len(variants) != len(engine.Variants()) {
+		t.Errorf("variants = %v, want all %d", variants, len(engine.Variants()))
+	}
+	for _, n := range dawgNames() {
+		if _, err := os.Stat(filepath.Join(dir, n)); err != nil {
+			t.Errorf("missing extracted %s: %v", n, err)
+		}
+	}
+}
+
+func TestExtractIgnoresUnexpectedAndTraversal(t *testing.T) {
+	dir := t.TempDir()
+	files := map[string][]byte{
+		"pkg/en_sowpods.dawg": []byte("ok"),   // a subdir path is stripped to its base
+		"README.txt":          []byte("junk"), // an unexpected name is ignored
+	}
+	// A traversal name with a recognised base must still land inside destDir.
+	traversal := &tar.Header{Name: "../ru_scrabble.dawg", Mode: 0o644, Size: 2, Typeflag: tar.TypeReg}
+	// A symlink, even named like a DAWG, is ignored.
+	symlink := &tar.Header{Name: "erudit_ru.dawg", Linkname: "/etc/passwd", Typeflag: tar.TypeSymlink}
+
+	if _, err := Extract(bytes.NewReader(tarGz(t, files, []*tar.Header{traversal, symlink})), dir); err != nil {
+		t.Fatalf("Extract: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "README.txt")); err == nil {
+		t.Error("README.txt was extracted; unexpected files must be ignored")
+	}
+	if _, err := os.Stat(filepath.Join(dir, "en_sowpods.dawg")); err != nil {
+		t.Errorf("en_sowpods.dawg not extracted from a subdir entry: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "ru_scrabble.dawg")); err != nil {
+		t.Errorf("ru_scrabble.dawg not extracted from a traversal entry: %v", err)
+	}
+	// Nothing escaped the destination directory.
+	if _, err := os.Stat(filepath.Join(filepath.Dir(dir), "ru_scrabble.dawg")); err == nil {
+		t.Error("path traversal wrote outside the destination directory")
+	}
+	if _, err := os.Stat(filepath.Join(dir, "erudit_ru.dawg")); err == nil {
+		t.Error("a symlink member was materialised")
+	}
+}
+
+func TestExtractRejectsOversizeMember(t *testing.T) {
+	old := maxMemberBytes
+	maxMemberBytes = 8
+	defer func() { maxMemberBytes = old }()
+
+	files := map[string][]byte{"en_sowpods.dawg": bytes.Repeat([]byte("x"), 64)}
+	if _, err := Extract(bytes.NewReader(tarGz(t, files, nil)), t.TempDir()); err == nil {
+		t.Error("Extract accepted an oversize member, want error")
+	}
+}
+
+func TestExtractRejectsTooManyEntries(t *testing.T) {
+	var extra []*tar.Header
+	for i := 0; i < maxEntries+1; i++ {
+		extra = append(extra, &tar.Header{Name: fmt.Sprintf("junk-%d.bin", i), Mode: 0o644, Size: 1, Typeflag: tar.TypeReg})
+	}
+	if _, err := Extract(bytes.NewReader(tarGz(t, nil, extra)), t.TempDir()); err == nil {
+		t.Error("Extract accepted an archive with too many entries, want error")
+	}
+}
+
+func TestManagerStageInstall(t *testing.T) {
+	dir := t.TempDir()
+	m := New(dir)
+
+	token, variants, err := m.Stage(bytes.NewReader(fullArchive(t)))
+	if err != nil {
+		t.Fatalf("Stage: %v", err)
+	}
+	if len(variants) != len(engine.Variants()) {
+		t.Fatalf("staged variants = %v, want all", variants)
+	}
+	staged, err := m.StagedDir(token)
+	if err != nil {
+		t.Fatalf("StagedDir: %v", err)
+	}
+	if !strings.Contains(staged, filepath.Join(".staging", token)) {
+		t.Errorf("staged dir %q not under .staging/%s", staged, token)
+	}
+
+	if m.VersionExists("v1.0.0") {
+		t.Fatal("v1.0.0 should not exist before install")
+	}
+	dest, err := m.Install(token, "v1.0.0")
+	if err != nil {
+		t.Fatalf("Install: %v", err)
+	}
+	if dest != filepath.Join(dir, "v1.0.0") {
+		t.Errorf("install dest = %q, want %q", dest, filepath.Join(dir, "v1.0.0"))
+	}
+	if !m.VersionExists("v1.0.0") {
+		t.Error("VersionExists(v1.0.0) = false after install")
+	}
+	for _, n := range dawgNames() {
+		if _, err := os.Stat(filepath.Join(dest, n)); err != nil {
+			t.Errorf("installed %s missing: %v", n, err)
+		}
+	}
+}
+
+func TestManagerInstallRejectsExistingVersion(t *testing.T) {
+	dir := t.TempDir()
+	m := New(dir)
+	token, _, err := m.Stage(bytes.NewReader(fullArchive(t)))
+	if err != nil {
+		t.Fatalf("Stage: %v", err)
+	}
+	if _, err := m.Install(token, "v2.0.0"); err != nil {
+		t.Fatalf("first Install: %v", err)
+	}
+	token2, _, err := m.Stage(bytes.NewReader(fullArchive(t)))
+	if err != nil {
+		t.Fatalf("second Stage: %v", err)
+	}
+	if _, err := m.Install(token2, "v2.0.0"); err == nil {
+		t.Error("Install overwrote an existing version, want error (versions are immutable)")
+	}
+}
+
+func TestStagedDirRejectsBadToken(t *testing.T) {
+	m := New(t.TempDir())
+	for _, bad := range []string{"", "../etc", "ABC", "zz", strings.Repeat("g", 32)} {
+		if _, err := m.StagedDir(bad); err == nil {
+			t.Errorf("StagedDir(%q) = nil error, want rejection", bad)
+		}
+	}
+}

backend/internal/engine/diff.go

@@ -0,0 +1,134 @@
+package engine
+
+import (
+	"bytes"
+	"fmt"
+	"maps"
+	"path/filepath"
+	"sort"
+
+	dawg "github.com/iliadenisov/dafsa"
+)
+
+// WordDiff is the set difference between two dictionaries of one variant: the
+// words present only in the new dictionary (Added) and only in the old one
+// (Removed), decoded to characters and each sorted by the variant's alphabet
+// order. It drives the admin dictionary-update preview.
+type WordDiff struct {
+	Added   []string
+	Removed []string
+}
+
+// DictFiles returns a copy of the variant-to-committed-DAWG-filename map. It lets
+// callers outside the package (the dictionary-admin upload validation) check an
+// archive against the expected file set without sharing the engine's own map.
+func DictFiles() map[Variant]string {
+	out := make(map[Variant]string, len(dictFiles))
+	maps.Copy(out, dictFiles)
+	return out
+}
+
+// OpenFinder loads the committed DAWG of variant v from dir and returns its
+// finder. The caller owns the finder and must Close it. It backs enumeration of
+// a staged, not-yet-registered dictionary version.
+func OpenFinder(dir string, v Variant) (dawg.Finder, error) {
+	name, ok := dictFiles[v]
+	if !ok {
+		return nil, fmt.Errorf("%w: %d", ErrUnknownVariant, v)
+	}
+	path := filepath.Join(dir, name)
+	finder, err := dawg.Load(path)
+	if err != nil {
+		return nil, fmt.Errorf("engine: load %s dictionary from %s: %w", v, path, err)
+	}
+	return finder, nil
+}
+
+// Finder returns the loaded finder for the (variant, version) pair so its words
+// can be enumerated, or ErrUnknownVariant / ErrUnknownVersion when that
+// dictionary is not resident. The finder remains owned by the registry; callers
+// must not Close it.
+func (r *Registry) Finder(v Variant, version string) (dawg.Finder, error) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	versions, ok := r.entries[v]
+	if !ok {
+		return nil, fmt.Errorf("%w: %s", ErrUnknownVariant, v)
+	}
+	e, ok := versions[version]
+	if !ok {
+		return nil, fmt.Errorf("%w: %s/%s", ErrUnknownVersion, v, version)
+	}
+	return e.finder, nil
+}
+
+// DiffWords compares the old and new finders of variant v and returns the words
+// added and removed, decoded through v's alphabet. Both dictionaries are
+// enumerated as alphabet-index bytes and merged; only the differing words are
+// decoded, so a full-dictionary comparison does not materialise two large string
+// sets.
+func DiffWords(v Variant, old, updated dawg.Finder) (WordDiff, error) {
+	rs, ok := v.ruleset()
+	if !ok {
+		return WordDiff{}, fmt.Errorf("%w: %d", ErrUnknownVariant, v)
+	}
+	oldWords := collectWords(old)
+	newWords := collectWords(updated)
+
+	var diff WordDiff
+	i, j := 0, 0
+	for i < len(oldWords) && j < len(newWords) {
+		switch cmp := bytes.Compare(oldWords[i], newWords[j]); {
+		case cmp == 0:
+			i++
+			j++
+		case cmp < 0:
+			s, err := rs.Alphabet.Decode(oldWords[i])
+			if err != nil {
+				return WordDiff{}, fmt.Errorf("engine: decode %s removed word: %w", v, err)
+			}
+			diff.Removed = append(diff.Removed, s)
+			i++
+		default:
+			s, err := rs.Alphabet.Decode(newWords[j])
+			if err != nil {
+				return WordDiff{}, fmt.Errorf("engine: decode %s added word: %w", v, err)
+			}
+			diff.Added = append(diff.Added, s)
+			j++
+		}
+	}
+	for ; i < len(oldWords); i++ {
+		s, err := rs.Alphabet.Decode(oldWords[i])
+		if err != nil {
+			return WordDiff{}, fmt.Errorf("engine: decode %s removed word: %w", v, err)
+		}
+		diff.Removed = append(diff.Removed, s)
+	}
+	for ; j < len(newWords); j++ {
+		s, err := rs.Alphabet.Decode(newWords[j])
+		if err != nil {
+			return WordDiff{}, fmt.Errorf("engine: decode %s added word: %w", v, err)
+		}
+		diff.Added = append(diff.Added, s)
+	}
+	return diff, nil
+}
+
+// collectWords enumerates every complete word of f as a copy of its
+// alphabet-index bytes, sorted ascending. The dawg already enumerates in index
+// order; the explicit sort makes the merge in DiffWords robust to that being an
+// implementation detail.
+func collectWords(f dawg.Finder) [][]byte {
+	out := make([][]byte, 0, f.NumAdded())
+	f.EnumerateB(func(_ int, word []byte, final bool) dawg.EnumerationResult {
+		if final && len(word) > 0 {
+			cp := make([]byte, len(word))
+			copy(cp, word)
+			out = append(out, cp)
+		}
+		return dawg.Continue
+	})
+	sort.Slice(out, func(a, b int) bool { return bytes.Compare(out[a], out[b]) < 0 })
+	return out
+}

backend/internal/engine/diff_test.go

@@ -0,0 +1,134 @@
+package engine
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/iliadenisov/alphabet"
+	dawg "github.com/iliadenisov/dafsa"
+)
+
+// buildFinderB builds an in-memory finder over idx from the given words, each
+// expressed as alphabet-index bytes. The words must be supplied in strictly
+// increasing alphabet-index order, as the builder requires.
+func buildFinderB(t *testing.T, idx alphabet.Indexer, words ...[]byte) dawg.Finder {
+	t.Helper()
+	b := dawg.New(idx)
+	for _, w := range words {
+		if err := b.AddB(w); err != nil {
+			t.Fatalf("addB %v: %v", w, err)
+		}
+	}
+	return b.Finish()
+}
+
+// mustDecode decodes index bytes through idx or fails the test.
+func mustDecode(t *testing.T, idx alphabet.Indexer, word []byte) string {
+	t.Helper()
+	s, err := idx.Decode(word)
+	if err != nil {
+		t.Fatalf("decode %v: %v", word, err)
+	}
+	return s
+}
+
+func equalStrings(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// TestDiffWords checks that DiffWords reports the words present only in the new
+// dictionary as added and those present only in the old one as removed, decoded
+// to characters through the variant's alphabet.
+func TestDiffWords(t *testing.T) {
+	rs, _ := VariantEnglish.ruleset()
+	idx := rs.Alphabet
+
+	old := buildFinderB(t, idx, []byte{0}, []byte{0, 1}, []byte{2})
+	defer func() { _ = old.Close() }()
+	updated := buildFinderB(t, idx, []byte{0}, []byte{2}, []byte{2, 3})
+	defer func() { _ = updated.Close() }()
+
+	diff, err := DiffWords(VariantEnglish, old, updated)
+	if err != nil {
+		t.Fatalf("DiffWords: %v", err)
+	}
+
+	wantAdded := []string{mustDecode(t, idx, []byte{2, 3})}
+	wantRemoved := []string{mustDecode(t, idx, []byte{0, 1})}
+	if !equalStrings(diff.Added, wantAdded) {
+		t.Errorf("added = %v, want %v", diff.Added, wantAdded)
+	}
+	if !equalStrings(diff.Removed, wantRemoved) {
+		t.Errorf("removed = %v, want %v", diff.Removed, wantRemoved)
+	}
+}
+
+// TestDiffWordsIdentical checks that comparing a dictionary with itself yields an
+// empty diff.
+func TestDiffWordsIdentical(t *testing.T) {
+	rs, _ := VariantEnglish.ruleset()
+	f := buildFinderB(t, rs.Alphabet, []byte{0}, []byte{1}, []byte{1, 2})
+	defer func() { _ = f.Close() }()
+
+	diff, err := DiffWords(VariantEnglish, f, f)
+	if err != nil {
+		t.Fatalf("DiffWords: %v", err)
+	}
+	if len(diff.Added) != 0 || len(diff.Removed) != 0 {
+		t.Errorf("diff = %+v, want empty", diff)
+	}
+}
+
+// TestDiffWordsUnknownVariant checks that an unrecognised variant is rejected.
+func TestDiffWordsUnknownVariant(t *testing.T) {
+	rs, _ := VariantEnglish.ruleset()
+	f := buildFinderB(t, rs.Alphabet, []byte{0})
+	defer func() { _ = f.Close() }()
+	if _, err := DiffWords(Variant(250), f, f); !errors.Is(err, ErrUnknownVariant) {
+		t.Errorf("err = %v, want ErrUnknownVariant", err)
+	}
+}
+
+// TestOpenFinder checks that OpenFinder loads a committed DAWG from a directory.
+func TestOpenFinder(t *testing.T) {
+	f, err := OpenFinder(testDictDir(), VariantEnglish)
+	if err != nil {
+		t.Fatalf("OpenFinder: %v", err)
+	}
+	defer func() { _ = f.Close() }()
+	if f.NumAdded() == 0 {
+		t.Error("english dictionary is empty")
+	}
+}
+
+// TestRegistryFinder checks that Finder returns the resident finder for a pair
+// and the right sentinel when the version is absent.
+func TestRegistryFinder(t *testing.T) {
+	if _, err := testReg.Finder(VariantEnglish, testVersion); err != nil {
+		t.Errorf("Finder(scrabble_en, %q): %v", testVersion, err)
+	}
+	if _, err := testReg.Finder(VariantEnglish, "absent"); !errors.Is(err, ErrUnknownVersion) {
+		t.Errorf("Finder absent version err = %v, want ErrUnknownVersion", err)
+	}
+}
+
+// TestDictFiles checks that DictFiles exposes the variant filename map as a copy
+// the caller cannot use to mutate the engine's own map.
+func TestDictFiles(t *testing.T) {
+	files := DictFiles()
+	if len(files) != len(Variants()) {
+		t.Fatalf("DictFiles has %d entries, want %d", len(files), len(Variants()))
+	}
+	files[VariantEnglish] = "tampered"
+	if again := DictFiles(); again[VariantEnglish] == "tampered" {
+		t.Error("DictFiles returned a shared map; mutating it changed the engine's map")
+	}
+}

backend/internal/engine/registry.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
 	"sync"
 
 	dawg "github.com/iliadenisov/dafsa"
@@ -83,7 +84,9 @@ func OpenWithVersions(dir, bootVersion string) (*Registry, error) {
 		return nil, fmt.Errorf("engine: scan dictionary dir %s: %w", dir, err)
 	}
 	for _, e := range entries {
-		if !e.IsDir() || e.Name() == bootVersion {
+		// Skip non-directories, the boot version (already loaded as the flat dir)
+		// and dot-prefixed directories (the upload staging area, dir/.staging/).
+		if !e.IsDir() || e.Name() == bootVersion || strings.HasPrefix(e.Name(), ".") {
 			continue
 		}
 		if _, err := r.LoadAvailable(filepath.Join(dir, e.Name()), e.Name()); err != nil {

backend/internal/engine/reload_test.go

@@ -91,6 +91,27 @@ func TestOpenWithVersionsScansSubdirs(t *testing.T) {
 	}
 }
 
+// TestOpenWithVersionsSkipsDotDirs verifies the boot scan ignores dot-prefixed
+// subdirectories (the upload staging area), so a half-extracted archive there
+// never becomes a resident version.
+func TestOpenWithVersionsSkipsDotDirs(t *testing.T) {
+	dir := t.TempDir()
+	for _, v := range Variants() {
+		copyDawg(t, testDictDir(), dir, v)
+	}
+	copyDawg(t, testDictDir(), filepath.Join(dir, ".staging"), VariantEnglish)
+
+	reg, err := OpenWithVersions(dir, "v1")
+	if err != nil {
+		t.Fatalf("open with versions: %v", err)
+	}
+	defer func() { _ = reg.Close() }()
+
+	if got := reg.Versions(VariantEnglish); len(got) != 1 || got[0] != "v1" {
+		t.Errorf("scrabble_en versions = %v, want only [v1] (.staging skipped)", got)
+	}
+}
+
 // TestReloadRegistersNewVersion verifies Load adds a second version to a variant
 // already resident, moves the latest pointer and keeps the earlier version.
 func TestReloadRegistersNewVersion(t *testing.T) {

backend/internal/game/service.go

@@ -9,6 +9,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/google/uuid"
@@ -30,12 +31,16 @@ type Service struct {
 	registry *engine.Registry
 	cache    *gameCache
 	locks    *keyedMutex
-	version  string
-	clock    func() time.Time
-	rng      func() int64
-	pub      notify.Publisher
-	metrics  *gameMetrics
-	log      *zap.Logger
+	// verMu guards version, the dictionary version new games pin. It is read on
+	// the game-create path and rewritten when an operator activates a new version
+	// through the admin console, so access is serialised.
+	verMu   sync.RWMutex
+	version string
+	clock   func() time.Time
+	rng     func() int64
+	pub     notify.Publisher
+	metrics *gameMetrics
+	log     *zap.Logger
 }
 
 // NewService constructs a Service. store and accounts wrap the same pool;
@@ -70,6 +75,62 @@ func (svc *Service) SetNotifier(p notify.Publisher) {
 	}
 }
 
+// activeVersion returns the dictionary version new games currently pin.
+func (svc *Service) activeVersion() string {
+	svc.verMu.RLock()
+	defer svc.verMu.RUnlock()
+	return svc.version
+}
+
+// ActiveVersion returns the dictionary version new games currently pin. It backs
+// the admin console's "active version" display.
+func (svc *Service) ActiveVersion() string {
+	return svc.activeVersion()
+}
+
+// InitActiveVersion reconciles the persisted active dictionary version with the
+// registry at startup. If a version was persisted and is resident, it becomes the
+// active version; otherwise the configured seed version is kept and persisted as
+// the initial active version. Call once during wiring, before serving traffic.
+func (svc *Service) InitActiveVersion(ctx context.Context) error {
+	persisted, ok, err := svc.store.GetActiveDictVersion(ctx)
+	if err != nil {
+		return err
+	}
+	if ok && svc.versionResident(persisted) {
+		svc.verMu.Lock()
+		svc.version = persisted
+		svc.verMu.Unlock()
+		return nil
+	}
+	return svc.store.SetActiveDictVersion(ctx, svc.activeVersion())
+}
+
+// SetActiveVersion records version as the active dictionary version, persisting it
+// and updating the in-memory pointer new games read. The caller must have made the
+// version resident in the registry first.
+func (svc *Service) SetActiveVersion(ctx context.Context, version string) error {
+	if err := svc.store.SetActiveDictVersion(ctx, version); err != nil {
+		return err
+	}
+	svc.verMu.Lock()
+	svc.version = version
+	svc.verMu.Unlock()
+	return nil
+}
+
+// versionResident reports whether any variant of version is loaded in the
+// registry, so a persisted active version pointing at a no-longer-present version
+// (e.g. after a volume loss) falls back to the seed.
+func (svc *Service) versionResident(version string) bool {
+	for _, v := range engine.Variants() {
+		if _, err := svc.registry.Solver(v, version); err == nil {
+			return true
+		}
+	}
+	return false
+}
+
 // Create starts and persists a new game seating the given accounts in turn order
 // (seat 0 first), deals the racks, and warms the live-game cache. It validates
 // the player count (2–4), the move clock, the hint allowance and that every seat
@@ -106,9 +167,12 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 	if seed == 0 {
 		seed = svc.rng()
 	}
+	// Capture the active version once so the engine game and the persisted
+	// dict_version agree even if an operator activates a new version concurrently.
+	version := svc.activeVersion()
 	g, err := engine.New(svc.registry, engine.Options{
 		Variant:              params.Variant,
-		Version:              svc.version,
+		Version:              version,
 		Players:              len(params.Seats),
 		Seed:                 seed,
 		DropoutTiles:         params.DropoutTiles,
@@ -128,7 +192,7 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 	ins := gameInsert{
 		id:                   id,
 		variant:              params.Variant.String(),
-		dictVersion:          svc.version,
+		dictVersion:          version,
 		seed:                 seed,
 		players:              len(params.Seats),
 		turnTimeoutSecs:      int(timeout / time.Second),
@@ -180,7 +244,7 @@ func (svc *Service) OpenOrJoin(ctx context.Context, accountID uuid.UUID, params
 	ins := gameInsert{
 		id:                   id,
 		variant:              params.Variant.String(),
-		dictVersion:          svc.version,
+		dictVersion:          svc.activeVersion(),
 		seed:                 seed,
 		players:              2,
 		turnTimeoutSecs:      int(timeout / time.Second),
@@ -759,7 +823,7 @@ func (svc *Service) DictionaryChanges(ctx context.Context) ([]DictionaryChange,
 }
 
 // MarkChangesApplied records that every pending accepted change for variant has
-// been folded into the dictionary version that was just hot-reloaded, removing
+// been folded into the dictionary version that was just installed, removing
 // them from DictionaryChanges. It returns the number of changes marked.
 func (svc *Service) MarkChangesApplied(ctx context.Context, variant engine.Variant, version string) (int64, error) {
 	return svc.store.MarkChangesApplied(ctx, variant.String(), version)

backend/internal/game/store.go

@@ -767,6 +767,41 @@ func (s *Store) MarkChangesApplied(ctx context.Context, variant, version string)
 	return n, nil
 }
 
+// GetActiveDictVersion returns the persisted active dictionary version and true,
+// or ("", false, nil) when none has been recorded yet (a fresh database). It reads
+// the dictionary_state singleton (docs/ARCHITECTURE.md §5).
+func (s *Store) GetActiveDictVersion(ctx context.Context) (string, bool, error) {
+	stmt := postgres.SELECT(table.DictionaryState.ActiveVersion).
+		FROM(table.DictionaryState).
+		WHERE(table.DictionaryState.ID.EQ(postgres.Bool(true)))
+	var row model.DictionaryState
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return "", false, nil
+		}
+		return "", false, fmt.Errorf("game: get active dict version: %w", err)
+	}
+	return row.ActiveVersion, true, nil
+}
+
+// SetActiveDictVersion records version as the active dictionary version, upserting
+// the dictionary_state singleton so the choice survives a restart.
+func (s *Store) SetActiveDictVersion(ctx context.Context, version string) error {
+	now := time.Now().UTC()
+	stmt := table.DictionaryState.
+		INSERT(table.DictionaryState.ID, table.DictionaryState.ActiveVersion, table.DictionaryState.UpdatedAt).
+		VALUES(true, version, postgres.TimestampzT(now)).
+		ON_CONFLICT(table.DictionaryState.ID).
+		DO_UPDATE(postgres.SET(
+			table.DictionaryState.ActiveVersion.SET(postgres.String(version)),
+			table.DictionaryState.UpdatedAt.SET(postgres.TimestampzT(now)),
+		))
+	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
+		return fmt.Errorf("game: set active dict version: %w", err)
+	}
+	return nil
+}
+
 // CountComplaints returns the number of complaints, optionally restricted to a
 // status, for the admin queue pager and the dashboard counts.
 func (s *Store) CountComplaints(ctx context.Context, status string) (int, error) {

backend/internal/game/types.go

@@ -248,7 +248,7 @@ type Complaint struct {
 // complaint: Add reports whether Word should be added (DispositionAcceptAdd) or
 // removed (DispositionAcceptRemove) for Variant. The admin console lists the
 // pending changes as the input to the offline DAWG rebuild; once a rebuilt
-// dictionary version is hot-reloaded they are marked applied.
+// dictionary version is installed they are marked applied.
 type DictionaryChange struct {
 	ComplaintID uuid.UUID
 	Variant     engine.Variant

backend/internal/inttest/dictionary_update_test.go

@@ -0,0 +1,220 @@
+//go:build integration
+
+package inttest
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"io"
+	"mime/multipart"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+
+	"scrabble/backend/internal/account"
+	"scrabble/backend/internal/engine"
+	"scrabble/backend/internal/game"
+	"scrabble/backend/internal/server"
+)
+
+// TestDictionaryUpdateFlow drives the admin dictionary update end to end over HTTP
+// against real stores and an isolated dictionary directory: upload a release
+// archive, preview the diff, install it, and confirm it becomes the active version,
+// is written to disk, survives a restart (a fresh service re-adopts it), pins new
+// games while leaving an in-progress game on its old version, and is immutable.
+func TestDictionaryUpdateFlow(t *testing.T) {
+	ctx := context.Background()
+
+	// Isolated dictionary directory seeded with the real DAWGs as the flat boot
+	// version v1.0.0, with its own registry and service so the shared fixtures are
+	// untouched.
+	dir := t.TempDir()
+	seedDawgs(t, dictDir(), dir)
+	reg, err := engine.OpenWithVersions(dir, "v1.0.0")
+	if err != nil {
+		t.Fatalf("open registry: %v", err)
+	}
+	defer func() { _ = reg.Close() }()
+
+	svc := newGameServiceOn(dir, "v1.0.0", reg)
+	if err := svc.InitActiveVersion(ctx); err != nil {
+		t.Fatalf("init active version: %v", err)
+	}
+	if got := svc.ActiveVersion(); got != "v1.0.0" {
+		t.Fatalf("active version = %q, want v1.0.0", got)
+	}
+
+	// An in-progress game pinned to the original version.
+	seats := []uuid.UUID{provisionAccount(t), provisionAccount(t)}
+	oldGame, err := svc.Create(ctx, game.CreateParams{Variant: engine.VariantEnglish, Seats: seats, TurnTimeout: 24 * time.Hour, Seed: 1})
+	if err != nil {
+		t.Fatalf("create old game: %v", err)
+	}
+	if oldGame.DictVersion != "v1.0.0" {
+		t.Fatalf("old game dict_version = %q, want v1.0.0", oldGame.DictVersion)
+	}
+
+	srv := server.New(":0", server.Deps{
+		Logger: zap.NewNop(), Accounts: account.NewStore(testDB), Games: svc, Registry: reg, DictDir: dir,
+	})
+	h := srv.Handler()
+	base := "http://admin.test/_gm"
+	archive := releaseArchive(t, dir)
+	const fileName = "scrabble-dawg-v9.9.9.tar.gz"
+
+	// Upload without a same-origin header is rejected by the CSRF guard.
+	if code, _ := consoleUpload(h, base+"/dictionary/upload", fileName, archive, ""); code != http.StatusForbidden {
+		t.Fatalf("upload without origin = %d, want 403", code)
+	}
+
+	// Upload with origin renders the preview carrying the version and a token.
+	code, body := consoleUpload(h, base+"/dictionary/upload", fileName, archive, "http://admin.test")
+	if code != http.StatusOK || !strings.Contains(body, "v9.9.9") {
+		t.Fatalf("upload = %d, has version=%v", code, strings.Contains(body, "v9.9.9"))
+	}
+	token := tokenFrom(t, body)
+
+	// Confirm installs, loads and activates the new version.
+	code, body = consoleDo(h, http.MethodPost, base+"/dictionary/install", "token="+token+"&version=v9.9.9", "http://admin.test")
+	if code != http.StatusOK || !strings.Contains(body, "Updated") {
+		t.Fatalf("install = %d, has Updated=%v", code, strings.Contains(body, "Updated"))
+	}
+
+	// The new version is active, resident for every variant, and written to disk.
+	if got := svc.ActiveVersion(); got != "v9.9.9" {
+		t.Fatalf("active version after install = %q, want v9.9.9", got)
+	}
+	for _, v := range engine.Variants() {
+		if _, err := reg.Solver(v, "v9.9.9"); err != nil {
+			t.Errorf("variant %s v9.9.9 not resident: %v", v, err)
+		}
+	}
+	if _, err := os.Stat(filepath.Join(dir, "v9.9.9", "en_sowpods.dawg")); err != nil {
+		t.Errorf("installed dawg missing on disk: %v", err)
+	}
+
+	// The choice survives a restart: a fresh service over the same DB and registry
+	// re-adopts the persisted active version.
+	restarted := newGameServiceOn(dir, "v1.0.0", reg)
+	if err := restarted.InitActiveVersion(ctx); err != nil {
+		t.Fatalf("restart init: %v", err)
+	}
+	if got := restarted.ActiveVersion(); got != "v9.9.9" {
+		t.Errorf("restarted active version = %q, want v9.9.9 (persisted)", got)
+	}
+
+	// New games pin the new version; the in-progress game keeps its own, still resident.
+	newGame, err := svc.Create(ctx, game.CreateParams{Variant: engine.VariantEnglish, Seats: []uuid.UUID{provisionAccount(t), provisionAccount(t)}, TurnTimeout: 24 * time.Hour, Seed: 2})
+	if err != nil {
+		t.Fatalf("create new game: %v", err)
+	}
+	if newGame.DictVersion != "v9.9.9" {
+		t.Errorf("new game dict_version = %q, want v9.9.9", newGame.DictVersion)
+	}
+	if _, err := reg.Solver(engine.VariantEnglish, oldGame.DictVersion); err != nil {
+		t.Errorf("old game's version %s no longer resident: %v", oldGame.DictVersion, err)
+	}
+
+	// Re-uploading the now-resident version is rejected (versions are immutable).
+	if _, body := consoleUpload(h, base+"/dictionary/upload", fileName, archive, "http://admin.test"); !strings.Contains(body, "Already resident") {
+		t.Errorf("re-upload of resident version not rejected: %q", body)
+	}
+}
+
+// newGameServiceOn builds a game service over the shared pool but a caller-supplied
+// dictionary directory, version and registry, for the isolated dictionary tests.
+func newGameServiceOn(dir, version string, reg *engine.Registry) *game.Service {
+	return game.NewService(
+		game.NewStore(testDB), account.NewStore(testDB), reg,
+		game.Config{DictDir: dir, DictVersion: version, TimeoutSweepInterval: time.Minute, CacheTTL: time.Hour},
+		zap.NewNop(),
+	)
+}
+
+// seedDawgs copies the committed DAWG of every variant from src into dst (flat).
+func seedDawgs(t *testing.T, src, dst string) {
+	t.Helper()
+	for _, name := range engine.DictFiles() {
+		copyFile(t, filepath.Join(src, name), filepath.Join(dst, name))
+	}
+}
+
+// releaseArchive packs the three DAWGs from dir into an in-memory gzip+tar release
+// archive, the shape consoleUploadDictionary expects.
+func releaseArchive(t *testing.T, dir string) []byte {
+	t.Helper()
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gz)
+	for _, name := range engine.DictFiles() {
+		data, err := os.ReadFile(filepath.Join(dir, name))
+		if err != nil {
+			t.Fatalf("read %s: %v", name, err)
+		}
+		if err := tw.WriteHeader(&tar.Header{Name: name, Mode: 0o644, Size: int64(len(data)), Typeflag: tar.TypeReg}); err != nil {
+			t.Fatalf("tar header %s: %v", name, err)
+		}
+		if _, err := tw.Write(data); err != nil {
+			t.Fatalf("tar write %s: %v", name, err)
+		}
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("close tar: %v", err)
+	}
+	if err := gz.Close(); err != nil {
+		t.Fatalf("close gzip: %v", err)
+	}
+	return buf.Bytes()
+}
+
+func copyFile(t *testing.T, src, dst string) {
+	t.Helper()
+	data, err := os.ReadFile(src)
+	if err != nil {
+		t.Fatalf("read %s: %v", src, err)
+	}
+	if err := os.WriteFile(dst, data, 0o644); err != nil {
+		t.Fatalf("write %s: %v", dst, err)
+	}
+}
+
+var tokenRE = regexp.MustCompile(`name="token" value="([0-9a-f]{32})"`)
+
+// tokenFrom extracts the staging token from a rendered preview page.
+func tokenFrom(t *testing.T, body string) string {
+	t.Helper()
+	m := tokenRE.FindStringSubmatch(body)
+	if m == nil {
+		t.Fatalf("no staging token in preview body:\n%s", body)
+	}
+	return m[1]
+}
+
+// consoleUpload posts a multipart archive to target as the "archive" file field,
+// optionally with an Origin header, returning the status and body.
+func consoleUpload(h http.Handler, target, filename string, data []byte, origin string) (int, string) {
+	var buf bytes.Buffer
+	mw := multipart.NewWriter(&buf)
+	fw, _ := mw.CreateFormFile("archive", filename)
+	_, _ = io.Copy(fw, bytes.NewReader(data))
+	_ = mw.Close()
+
+	req := httptest.NewRequest(http.MethodPost, target, &buf)
+	req.Header.Set("Content-Type", mw.FormDataContentType())
+	if origin != "" {
+		req.Header.Set("Origin", origin)
+	}
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	return rec.Code, rec.Body.String()
+}

backend/internal/postgres/jet/backend/model/dictionary_state.go

@@ -0,0 +1,18 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package model
+
+import (
+	"time"
+)
+
+type DictionaryState struct {
+	ID            bool `sql:"primary_key"`
+	ActiveVersion string
+	UpdatedAt     time.Time
+}

backend/internal/postgres/jet/backend/table/dictionary_state.go

@@ -0,0 +1,84 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var DictionaryState = newDictionaryStateTable("backend", "dictionary_state", "")
+
+type dictionaryStateTable struct {
+	postgres.Table
+
+	// Columns
+	ID            postgres.ColumnBool
+	ActiveVersion postgres.ColumnString
+	UpdatedAt     postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type DictionaryStateTable struct {
+	dictionaryStateTable
+
+	EXCLUDED dictionaryStateTable
+}
+
+// AS creates new DictionaryStateTable with assigned alias
+func (a DictionaryStateTable) AS(alias string) *DictionaryStateTable {
+	return newDictionaryStateTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new DictionaryStateTable with assigned schema name
+func (a DictionaryStateTable) FromSchema(schemaName string) *DictionaryStateTable {
+	return newDictionaryStateTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new DictionaryStateTable with assigned table prefix
+func (a DictionaryStateTable) WithPrefix(prefix string) *DictionaryStateTable {
+	return newDictionaryStateTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new DictionaryStateTable with assigned table suffix
+func (a DictionaryStateTable) WithSuffix(suffix string) *DictionaryStateTable {
+	return newDictionaryStateTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newDictionaryStateTable(schemaName, tableName, alias string) *DictionaryStateTable {
+	return &DictionaryStateTable{
+		dictionaryStateTable: newDictionaryStateTableImpl(schemaName, tableName, alias),
+		EXCLUDED:             newDictionaryStateTableImpl("", "excluded", ""),
+	}
+}
+
+func newDictionaryStateTableImpl(schemaName, tableName, alias string) dictionaryStateTable {
+	var (
+		IDColumn            = postgres.BoolColumn("id")
+		ActiveVersionColumn = postgres.StringColumn("active_version")
+		UpdatedAtColumn     = postgres.TimestampzColumn("updated_at")
+		allColumns          = postgres.ColumnList{IDColumn, ActiveVersionColumn, UpdatedAtColumn}
+		mutableColumns      = postgres.ColumnList{ActiveVersionColumn, UpdatedAtColumn}
+		defaultColumns      = postgres.ColumnList{IDColumn, UpdatedAtColumn}
+	)
+
+	return dictionaryStateTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		ID:            IDColumn,
+		ActiveVersion: ActiveVersionColumn,
+		UpdatedAt:     UpdatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}

backend/internal/postgres/jet/backend/table/table_use_schema.go

@@ -15,6 +15,7 @@ func UseSchema(schema string) {
 	Blocks = Blocks.FromSchema(schema)
 	ChatMessages = ChatMessages.FromSchema(schema)
 	Complaints = Complaints.FromSchema(schema)
+	DictionaryState = DictionaryState.FromSchema(schema)
 	EmailConfirmations = EmailConfirmations.FromSchema(schema)
 	FriendCodes = FriendCodes.FromSchema(schema)
 	Friendships = Friendships.FromSchema(schema)

backend/internal/postgres/migrations/00001_baseline.sql

@@ -158,7 +158,7 @@ CREATE TABLE game_moves (
 -- Word-check complaints captured in the context of a game's pinned dictionary. The
 -- admin review queue resolves them with a disposition that also feeds the offline
 -- dictionary-rebuild pipeline: an accepted complaint records whether the word is to be
--- added or removed, and is marked applied once a rebuilt version is hot-reloaded.
+-- added or removed, and is marked applied once a rebuilt version is installed.
 CREATE TABLE complaints (
     complaint_id       uuid        PRIMARY KEY,
     complainant_id     uuid        NOT NULL REFERENCES accounts (account_id),
@@ -180,6 +180,19 @@ CREATE TABLE complaints (
 );
 CREATE INDEX complaints_status_idx ON complaints (status);
 
+-- The active dictionary version new games pin, kept as the single source of truth
+-- so it survives a restart (the in-memory engine.Registry is rebuilt from the
+-- dictionary directory on every boot). A singleton row: id is always true. The
+-- admin dictionary-update flow sets active_version after it writes and loads a new
+-- version; new games read it, while in-flight games keep the version stamped on
+-- their games.dict_version (docs/ARCHITECTURE.md §5).
+CREATE TABLE dictionary_state (
+    id             boolean     PRIMARY KEY DEFAULT true,
+    active_version text        NOT NULL,
+    updated_at     timestamptz NOT NULL DEFAULT now(),
+    CONSTRAINT dictionary_state_singleton_chk CHECK (id)
+);
+
 -- Per-account lifetime statistics, recomputed incrementally on each game finish.
 -- Guests have no durable stats. A draw increments draws only. max_word_points is the
 -- best single move score (folding in every word the move formed and the all-tiles bonus).

backend/internal/server/handlers_admin_console.go

@@ -7,7 +7,6 @@ import (
 	"html/template"
 	"net/http"
 	"net/url"
-	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
@@ -18,6 +17,7 @@ import (
 
 	"scrabble/backend/internal/account"
 	"scrabble/backend/internal/adminconsole"
+	"scrabble/backend/internal/dictadmin"
 	"scrabble/backend/internal/engine"
 	"scrabble/backend/internal/game"
 	"scrabble/backend/internal/ratewatch"
@@ -60,7 +60,8 @@ func (s *Server) registerConsole(router *gin.Engine) {
 	gm.GET("/messages", s.consoleMessages)
 	gm.GET("/messages.csv", s.consoleMessagesCSV)
 	gm.GET("/dictionary", s.consoleDictionary)
-	gm.POST("/dictionary/reload", s.consoleReloadDictionary)
+	gm.POST("/dictionary/upload", s.consoleUploadDictionary)
+	gm.POST("/dictionary/install", s.consoleInstallDictionary)
 	gm.POST("/dictionary/changes/apply", s.consoleApplyChanges)
 	gm.GET("/broadcast", s.consoleBroadcast)
 	gm.POST("/broadcast", s.consolePostBroadcast)
@@ -70,7 +71,7 @@ func (s *Server) registerConsole(router *gin.Engine) {
 // dictionary versions.
 func (s *Server) consoleDashboard(c *gin.Context) {
 	ctx := c.Request.Context()
-	view := adminconsole.DashboardView{Variants: s.variantVersions()}
+	view := adminconsole.DashboardView{Variants: s.variantVersions(), ActiveVersion: s.games.ActiveVersion()}
 	view.Accounts, _ = s.accounts.CountAccounts(ctx)
 	view.Games, _ = s.games.CountGames(ctx, "")
 	view.ActiveGames, _ = s.games.CountGames(ctx, game.StatusActive)
@@ -473,7 +474,7 @@ func (s *Server) consoleResolveComplaint(c *gin.Context) {
 
 // consoleDictionary renders the resident versions and the pending wordlist changes.
 func (s *Server) consoleDictionary(c *gin.Context) {
-	view := adminconsole.DictionaryView{Variants: s.variantVersions()}
+	view := adminconsole.DictionaryView{Variants: s.variantVersions(), ActiveVersion: s.games.ActiveVersion()}
 	if changes, err := s.games.DictionaryChanges(c.Request.Context()); err == nil {
 		for _, ch := range changes {
 			action := "remove"
@@ -486,28 +487,172 @@ func (s *Server) consoleDictionary(c *gin.Context) {
 	s.renderConsole(c, "dictionary", "dictionary", "Dictionary", view)
 }
 
-// consoleReloadDictionary hot-loads a dictionary version from its subdirectory.
-func (s *Server) consoleReloadDictionary(c *gin.Context) {
-	version := trimForm(c, "version")
-	if version == "" {
-		s.renderConsoleMessage(c, "Reload failed", "a version is required", "/_gm/dictionary")
+// previewSampleCap bounds how many added/removed words the update preview lists per
+// variant; the full totals are always shown.
+const previewSampleCap = 200
+
+// largeRemovalThreshold flags a removal large enough that the operator should pause
+// before confirming: a rebuilt dictionary normally drops a handful of words, not
+// thousands.
+const largeRemovalThreshold = 1000
+
+// consoleUploadDictionary accepts a scrabble-dawg release archive, stages it under
+// the dictionary directory and renders the per-variant word diff against the active
+// dictionary. The operator confirms it with consoleInstallDictionary. The archive
+// is bounded, its file name fixes the version, and a version already resident is
+// rejected (versions are immutable).
+func (s *Server) consoleUploadDictionary(c *gin.Context) {
+	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, dictadmin.MaxArchiveBytes)
+	file, header, err := c.Request.FormFile("archive")
+	if err != nil {
+		s.renderConsoleMessage(c, "Upload failed", "choose a scrabble-dawg-vX.Y.Z.tar.gz archive (max 64 MiB)", "/_gm/dictionary")
 		return
 	}
-	dir := filepath.Join(s.dictDir, version)
-	loaded, err := s.registry.LoadAvailable(dir, version)
+	defer func() { _ = file.Close() }()
+
+	version, err := dictadmin.ParseVersionFromName(header.Filename)
+	if err != nil {
+		s.renderConsoleMessage(c, "Upload failed", "the file name must be scrabble-dawg-vX.Y.Z.tar.gz", "/_gm/dictionary")
+		return
+	}
+	if s.versionResident(version) {
+		s.renderConsoleMessage(c, "Already resident", fmt.Sprintf("version %s is already loaded; versions are immutable", version), "/_gm/dictionary")
+		return
+	}
+
+	mgr := dictadmin.New(s.dictDir)
+	token, variants, err := mgr.Stage(file)
 	if err != nil {
 		s.consoleError(c, err)
 		return
 	}
-	if len(loaded) == 0 {
-		s.renderConsoleMessage(c, "Nothing loaded", "no dictionary files found in "+dir, "/_gm/dictionary")
+	if len(variants) != len(engine.Variants()) {
+		mgr.Discard(token)
+		s.renderConsoleMessage(c, "Incomplete archive",
+			fmt.Sprintf("the archive carries %d of %d variants; a release must contain all of them", len(variants), len(engine.Variants())),
+			"/_gm/dictionary")
 		return
 	}
-	names := make([]string, len(loaded))
-	for i, v := range loaded {
-		names[i] = v.String()
+
+	staged, err := mgr.StagedDir(token)
+	if err != nil {
+		s.consoleError(c, err)
+		return
 	}
-	s.renderConsoleMessage(c, "Reloaded", fmt.Sprintf("loaded %v as version %q", names, version), "/_gm/dictionary")
+	rows, err := s.diffStaged(staged, variants)
+	if err != nil {
+		mgr.Discard(token)
+		s.consoleError(c, err)
+		return
+	}
+	s.renderConsole(c, "dictionary_preview", "dictionary", "Dictionary update", adminconsole.DictionaryPreviewView{
+		Version:       version,
+		Token:         token,
+		ActiveVersion: s.games.ActiveVersion(),
+		Variants:      rows,
+	})
+}
+
+// consoleInstallDictionary promotes a staged upload into its version directory,
+// loads it into the registry and makes it the active version new games pin. The
+// version is taken from the (editable) form field, re-validated and checked for
+// immutability.
+func (s *Server) consoleInstallDictionary(c *gin.Context) {
+	token := trimForm(c, "token")
+	version := trimForm(c, "version")
+	if !dictadmin.ValidVersion(version) {
+		s.renderConsoleMessage(c, "Install failed", "the version must look like vX.Y.Z", "/_gm/dictionary")
+		return
+	}
+	if s.versionResident(version) {
+		s.renderConsoleMessage(c, "Already resident", fmt.Sprintf("version %s is already loaded; versions are immutable", version), "/_gm/dictionary")
+		return
+	}
+
+	mgr := dictadmin.New(s.dictDir)
+	dest, err := mgr.Install(token, version)
+	if err != nil {
+		s.consoleError(c, err)
+		return
+	}
+	loaded, err := s.registry.LoadAvailable(dest, version)
+	if err != nil {
+		s.consoleError(c, err)
+		return
+	}
+	if len(loaded) != len(engine.Variants()) {
+		s.renderConsoleMessage(c, "Install incomplete",
+			fmt.Sprintf("loaded %d of %d variants from %s", len(loaded), len(engine.Variants()), version), "/_gm/dictionary")
+		return
+	}
+	if err := s.games.SetActiveVersion(c.Request.Context(), version); err != nil {
+		s.consoleError(c, err)
+		return
+	}
+	s.renderConsoleMessage(c, "Updated",
+		fmt.Sprintf("dictionary %s installed and activated; new games now use it, games in progress keep their version", version),
+		"/_gm/dictionary")
+}
+
+// diffStaged computes the word diff of each staged variant against the active
+// dictionary, projected into the preview rows.
+func (s *Server) diffStaged(staged string, variants []engine.Variant) ([]adminconsole.VariantDiffRow, error) {
+	active := s.games.ActiveVersion()
+	rows := make([]adminconsole.VariantDiffRow, 0, len(variants))
+	for _, v := range variants {
+		newFinder, err := engine.OpenFinder(staged, v)
+		if err != nil {
+			return nil, err
+		}
+		oldFinder, err := s.registry.Finder(v, active)
+		if err != nil {
+			_ = newFinder.Close()
+			return nil, fmt.Errorf("active dictionary %s/%s not resident: %w", v, active, err)
+		}
+		diff, err := engine.DiffWords(v, oldFinder, newFinder)
+		_ = newFinder.Close()
+		if err != nil {
+			return nil, err
+		}
+		rows = append(rows, diffRow(v, diff))
+	}
+	return rows, nil
+}
+
+// diffRow projects a variant's word diff into its preview row, capping the sample
+// lists and flagging a large removal.
+func diffRow(v engine.Variant, d engine.WordDiff) adminconsole.VariantDiffRow {
+	added, addedTrunc := sampleWords(d.Added)
+	removed, removedTrunc := sampleWords(d.Removed)
+	return adminconsole.VariantDiffRow{
+		Variant:          v.String(),
+		AddedCount:       len(d.Added),
+		RemovedCount:     len(d.Removed),
+		AddedSample:      added,
+		RemovedSample:    removed,
+		AddedTruncated:   addedTrunc,
+		RemovedTruncated: removedTrunc,
+		LargeRemoval:     len(d.Removed) >= largeRemovalThreshold,
+	}
+}
+
+// sampleWords returns at most previewSampleCap words and whether the list was cut.
+func sampleWords(words []string) ([]string, bool) {
+	if len(words) <= previewSampleCap {
+		return words, false
+	}
+	return words[:previewSampleCap], true
+}
+
+// versionResident reports whether version is loaded for any variant (covering the
+// flat seed and every uploaded subdirectory), backing the immutability guard.
+func (s *Server) versionResident(version string) bool {
+	for _, v := range engine.Variants() {
+		if _, err := s.registry.Finder(v, version); err == nil {
+			return true
+		}
+	}
+	return false
 }
 
 // consoleApplyChanges marks a variant's pending accepted changes applied in a

backend/internal/server/server.go

@@ -63,9 +63,10 @@ type Deps struct {
 	// Links drives account linking & merge: the /api/v1/user/link
 	// endpoints. A nil Links disables them.
 	Links *link.Service
-	// Registry holds the resident dictionaries; the admin console reads
-	// its versions and hot-reloads new ones. DictDir is the dictionary directory a
-	// reload reads a version subdirectory from. A nil Registry disables the console.
+	// Registry holds the resident dictionaries; the admin console reads its
+	// versions and installs new ones uploaded through it. DictDir is the dictionary
+	// directory the console stages uploads in and writes version subdirectories to.
+	// A nil Registry disables the console.
 	Registry *engine.Registry
 	DictDir  string
 	// Connector is the backend's Telegram connector client for operator broadcasts;