feat(profile): advertise per-variant dictionary versions for offline preload

The Profile now carries dict_versions (game variant -> current dictionary
version), populated from the dictionary registry at the profileResponse
choke point, so an installed PWA can preload the matching dawg per enabled
variant off the existing cold-start profile request instead of adding a
round-trip for a rare feature.

Wire path: FBS DictVersion table + Profile.dict_versions (additive,
backward-compatible trailing field) -> backend dto/registry -> gateway
ProfileResp + FBS encoder -> client codec decode into a per-variant map on
model.Profile. Empty in a degenerate no-dictionary deployment; the mock
serves v1.3.0 for all three variants. Codec decode covered by a
bite-tested round-trip unit test.

backend/internal/server/banner.go

@@ -8,6 +8,7 @@ import (
 
 	"scrabble/backend/internal/account"
 	"scrabble/backend/internal/ads"
+	"scrabble/backend/internal/engine"
 	"scrabble/backend/internal/notify"
 )
 
@@ -56,9 +57,34 @@ func (s *Server) profileResponse(ctx context.Context, acc account.Account) profi
 	r := profileResponseFor(acc)
 	r.Banner = s.bannerFor(ctx, acc)
 	s.fillLinkedIdentities(ctx, &r, acc.ID)
+	r.DictVersions = s.currentDictVersions()
 	return r
 }
 
+// currentDictVersions reports the current dictionary version of every game variant with a
+// resident dictionary, as engine.Variant stable labels. It backs profileResponse.DictVersions
+// so an offline-capable client preloads the matching dawg per variant off the cold-start
+// profile. A variant without a loaded dictionary is omitted (Registry.Latest reports
+// ErrUnknownVariant); the returned slice is nil only when no variant is resident.
+func (s *Server) currentDictVersions() []dictVersion {
+	if s.registry == nil {
+		return nil // no dictionary registry wired (e.g. a minimal test server): advertise none
+	}
+	variants := []engine.Variant{engine.VariantEnglish, engine.VariantRussianScrabble, engine.VariantErudit}
+	out := make([]dictVersion, 0, len(variants))
+	for _, v := range variants {
+		version, _, err := s.registry.Latest(v)
+		if err != nil {
+			continue
+		}
+		out = append(out, dictVersion{Variant: v.String(), Version: version})
+	}
+	if len(out) == 0 {
+		return nil
+	}
+	return out
+}
+
 // fillLinkedIdentities sets the profile's confirmed email address and platform-linked
 // flags from the account's identities, so the client offers the right link / unlink /
 // change-email controls. A read failure leaves them zero (no controls), logged as a

backend/internal/server/dto.go

@@ -63,6 +63,20 @@ type profileResponse struct {
 	Email          string `json:"email"`
 	TelegramLinked bool   `json:"telegram_linked"`
 	VkLinked       bool   `json:"vk_linked"`
+	// DictVersions lists the current dictionary version per game variant (engine.Variant
+	// stable labels). An installed PWA preparing for offline play reads it to preload the
+	// right dawg per enabled variant off this cold-start response, without an extra request.
+	// Filled outside the pure projection (it reads the dictionary registry), so it is empty
+	// for callers that build the DTO without a Server. See Server.profileResponse.
+	DictVersions []dictVersion `json:"dict_versions,omitempty"`
+}
+
+// dictVersion pairs a game variant's stable label (engine.Variant.String) with its current
+// dictionary version. profileResponse.DictVersions carries the set so an offline-capable
+// client preloads the matching dawg per variant.
+type dictVersion struct {
+	Variant string `json:"variant"`
+	Version string `json:"version"`
 }
 
 // tileDTO is one placed (or to-place) tile.

gateway/internal/backendclient/api.go

@@ -42,6 +42,15 @@ type ProfileResp struct {
 	Email          string `json:"email"`
 	TelegramLinked bool   `json:"telegram_linked"`
 	VkLinked       bool   `json:"vk_linked"`
+	// DictVersions is the current dictionary version per game variant, forwarded verbatim
+	// into the Profile payload so an offline-capable client preloads the matching dawg.
+	DictVersions []DictVersion `json:"dict_versions,omitempty"`
+}
+
+// DictVersion pairs a game variant's stable label with its current dictionary version.
+type DictVersion struct {
+	Variant string `json:"variant"`
+	Version string `json:"version"`
 }
 
 // BannerResp is the advertising-banner block of an eligible viewer's profile: the

gateway/internal/transcode/encode.go

@@ -95,6 +95,7 @@ func encodeProfile(p backendclient.ProfileResp) []byte {
 		banner = encodeBanner(b, *p.Banner)
 	}
 	prefs := buildStringVector(b, p.VariantPreferences, fb.ProfileStartVariantPreferencesVector)
+	dictVersions := encodeDictVersions(b, p.DictVersions)
 	fb.ProfileStart(b)
 	fb.ProfileAddUserId(b, uid)
 	fb.ProfileAddDisplayName(b, name)
@@ -111,6 +112,9 @@ func encodeProfile(p backendclient.ProfileResp) []byte {
 	fb.ProfileAddEmail(b, email)
 	fb.ProfileAddTelegramLinked(b, p.TelegramLinked)
 	fb.ProfileAddVkLinked(b, p.VkLinked)
+	if dictVersions != 0 {
+		fb.ProfileAddDictVersions(b, dictVersions)
+	}
 	if p.Banner != nil {
 		fb.ProfileAddBanner(b, banner)
 	}
@@ -118,6 +122,31 @@ func encodeProfile(p backendclient.ProfileResp) []byte {
 	return b.FinishedBytes()
 }
 
+// encodeDictVersions builds the Profile's dict_versions vector — one DictVersion table per
+// variant/version pair — and returns its offset, or 0 when there are none (the field is then
+// omitted). Every child table and its strings are created before the vector is opened, per the
+// FlatBuffers rule against nesting a table under one still being built; the caller invokes it
+// before ProfileStart for the same reason.
+func encodeDictVersions(b *flatbuffers.Builder, dvs []backendclient.DictVersion) flatbuffers.UOffsetT {
+	if len(dvs) == 0 {
+		return 0
+	}
+	offsets := make([]flatbuffers.UOffsetT, len(dvs))
+	for i, dv := range dvs {
+		variant := b.CreateString(dv.Variant)
+		version := b.CreateString(dv.Version)
+		fb.DictVersionStart(b)
+		fb.DictVersionAddVariant(b, variant)
+		fb.DictVersionAddVersion(b, version)
+		offsets[i] = fb.DictVersionEnd(b)
+	}
+	fb.ProfileStartDictVersionsVector(b, len(offsets))
+	for i := len(offsets) - 1; i >= 0; i-- {
+		b.PrependUOffsetT(offsets[i])
+	}
+	return b.EndVector(len(offsets))
+}
+
 // optString creates a FlatBuffers string for a non-empty value, or 0 to omit the
 // optional field (the client then reads it as absent).
 func optString(b *flatbuffers.Builder, s string) flatbuffers.UOffsetT {

pkg/fbs/scrabble.fbs

@@ -223,6 +223,13 @@ table BannerInfo {
 // suppresses out-of-app platform push, leaving only the in-app live stream. banner
 // carries the advertising-banner block for an eligible viewer, absent otherwise
 // (all added trailing — backward-compatible).
+// DictVersion is one variant's current dictionary version, carried on the profile so an offline
+// client learns it from an existing cold-start request (no extra call for a rarely-used feature).
+table DictVersion {
+  variant:string;
+  version:string;
+}
+
 table Profile {
   user_id:string;
   display_name:string;
@@ -245,6 +252,10 @@ table Profile {
   email:string;
   telegram_linked:bool;
   vk_linked:bool;
+  // dict_versions carries each variant's current dictionary version so an offline client can
+  // preload the right dictionary and pin a new local game without a separate request (added
+  // trailing — backward-compatible).
+  dict_versions:[DictVersion];
 }
 
 // BlockStatus reports the caller's current manual block. The UI fetches it after any operation

pkg/fbs/scrabblefb/DictVersion.go

@@ -0,0 +1,71 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type DictVersion struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsDictVersion(buf []byte, offset flatbuffers.UOffsetT) *DictVersion {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &DictVersion{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishDictVersionBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsDictVersion(buf []byte, offset flatbuffers.UOffsetT) *DictVersion {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &DictVersion{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedDictVersionBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *DictVersion) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *DictVersion) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *DictVersion) Variant() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *DictVersion) Version() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func DictVersionStart(builder *flatbuffers.Builder) {
+	builder.StartObject(2)
+}
+func DictVersionAddVariant(builder *flatbuffers.Builder, variant flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(variant), 0)
+}
+func DictVersionAddVersion(builder *flatbuffers.Builder, version flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(version), 0)
+}
+func DictVersionEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

pkg/fbs/scrabblefb/Profile.go

@@ -211,8 +211,28 @@ func (rcv *Profile) MutateVkLinked(n bool) bool {
 	return rcv._tab.MutateBoolSlot(34, n)
 }
 
+func (rcv *Profile) DictVersions(obj *DictVersion, j int) bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(36))
+	if o != 0 {
+		x := rcv._tab.Vector(o)
+		x += flatbuffers.UOffsetT(j) * 4
+		x = rcv._tab.Indirect(x)
+		obj.Init(rcv._tab.Bytes, x)
+		return true
+	}
+	return false
+}
+
+func (rcv *Profile) DictVersionsLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(36))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
 func ProfileStart(builder *flatbuffers.Builder) {
-	builder.StartObject(16)
+	builder.StartObject(17)
 }
 func ProfileAddUserId(builder *flatbuffers.Builder, userId flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(userId), 0)
@@ -265,6 +285,12 @@ func ProfileAddTelegramLinked(builder *flatbuffers.Builder, telegramLinked bool)
 func ProfileAddVkLinked(builder *flatbuffers.Builder, vkLinked bool) {
 	builder.PrependBoolSlot(15, vkLinked, false)
 }
+func ProfileAddDictVersions(builder *flatbuffers.Builder, dictVersions flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(16, flatbuffers.UOffsetT(dictVersions), 0)
+}
+func ProfileStartDictVersionsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
 func ProfileEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }

ui/src/gen/fbs/scrabblefb.ts

@@ -17,6 +17,7 @@ export { ChatPostRequest } from './scrabblefb/chat-post-request.js';
 export { CheckWordRequest } from './scrabblefb/check-word-request.js';
 export { ComplaintRequest } from './scrabblefb/complaint-request.js';
 export { CreateInvitationRequest } from './scrabblefb/create-invitation-request.js';
+export { DictVersion } from './scrabblefb/dict-version.js';
 export { DraftRequest } from './scrabblefb/draft-request.js';
 export { DraftView } from './scrabblefb/draft-view.js';
 export { EmailConfirmLinkRequest } from './scrabblefb/email-confirm-link-request.js';

ui/src/gen/fbs/scrabblefb/dict-version.ts

@@ -0,0 +1,60 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+export class DictVersion {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):DictVersion {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsDictVersion(bb:flatbuffers.ByteBuffer, obj?:DictVersion):DictVersion {
+  return (obj || new DictVersion()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsDictVersion(bb:flatbuffers.ByteBuffer, obj?:DictVersion):DictVersion {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new DictVersion()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+variant():string|null
+variant(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+variant(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+version():string|null
+version(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+version(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+static startDictVersion(builder:flatbuffers.Builder) {
+  builder.startObject(2);
+}
+
+static addVariant(builder:flatbuffers.Builder, variantOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, variantOffset, 0);
+}
+
+static addVersion(builder:flatbuffers.Builder, versionOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(1, versionOffset, 0);
+}
+
+static endDictVersion(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createDictVersion(builder:flatbuffers.Builder, variantOffset:flatbuffers.Offset, versionOffset:flatbuffers.Offset):flatbuffers.Offset {
+  DictVersion.startDictVersion(builder);
+  DictVersion.addVariant(builder, variantOffset);
+  DictVersion.addVersion(builder, versionOffset);
+  return DictVersion.endDictVersion(builder);
+}
+}

ui/src/gen/fbs/scrabblefb/profile.ts

@@ -3,6 +3,7 @@
 import * as flatbuffers from 'flatbuffers';
 
 import { BannerInfo } from '../scrabblefb/banner-info.js';
+import { DictVersion } from '../scrabblefb/dict-version.js';
 
 
 export class Profile {
@@ -124,8 +125,18 @@ vkLinked():boolean {
   return offset ? !!this.bb!.readInt8(this.bb_pos + offset) : false;
 }
 
+dictVersions(index: number, obj?:DictVersion):DictVersion|null {
+  const offset = this.bb!.__offset(this.bb_pos, 36);
+  return offset ? (obj || new DictVersion()).__init(this.bb!.__indirect(this.bb!.__vector(this.bb_pos + offset) + index * 4), this.bb!) : null;
+}
+
+dictVersionsLength():number {
+  const offset = this.bb!.__offset(this.bb_pos, 36);
+  return offset ? this.bb!.__vector_len(this.bb_pos + offset) : 0;
+}
+
 static startProfile(builder:flatbuffers.Builder) {
-  builder.startObject(16);
+  builder.startObject(17);
 }
 
 static addUserId(builder:flatbuffers.Builder, userIdOffset:flatbuffers.Offset) {
@@ -204,6 +215,22 @@ static addVkLinked(builder:flatbuffers.Builder, vkLinked:boolean) {
   builder.addFieldInt8(15, +vkLinked, +false);
 }
 
+static addDictVersions(builder:flatbuffers.Builder, dictVersionsOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(16, dictVersionsOffset, 0);
+}
+
+static createDictVersionsVector(builder:flatbuffers.Builder, data:flatbuffers.Offset[]):flatbuffers.Offset {
+  builder.startVector(4, data.length, 4);
+  for (let i = data.length - 1; i >= 0; i--) {
+    builder.addOffset(data[i]!);
+  }
+  return builder.endVector();
+}
+
+static startDictVersionsVector(builder:flatbuffers.Builder, numElems:number) {
+  builder.startVector(4, numElems, 4);
+}
+
 static endProfile(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;

ui/src/lib/codec.test.ts

@@ -712,6 +712,28 @@ describe('codec', () => {
     expect(decodeProfile(b.asUint8Array()).variantPreferences).toEqual(['erudit_ru', 'scrabble_en']);
   });
 
+  it('decodes the profile dictionary versions into a per-variant map', () => {
+    const b = new Builder(128);
+    const uid = b.createString('u-1');
+    const en = fb.DictVersion.createDictVersion(b, b.createString('scrabble_en'), b.createString('v1.3.0'));
+    const er = fb.DictVersion.createDictVersion(b, b.createString('erudit_ru'), b.createString('v1.2.0'));
+    const vec = fb.Profile.createDictVersionsVector(b, [en, er]);
+    fb.Profile.startProfile(b);
+    fb.Profile.addUserId(b, uid);
+    fb.Profile.addDictVersions(b, vec);
+    b.finish(fb.Profile.endProfile(b));
+    expect(decodeProfile(b.asUint8Array()).dictVersions).toEqual({ scrabble_en: 'v1.3.0', erudit_ru: 'v1.2.0' });
+  });
+
+  it('decodes an absent dict_versions vector to an empty map', () => {
+    const b = new Builder(64);
+    const uid = b.createString('u-1');
+    fb.Profile.startProfile(b);
+    fb.Profile.addUserId(b, uid);
+    b.finish(fb.Profile.endProfile(b));
+    expect(decodeProfile(b.asUint8Array()).dictVersions).toEqual({});
+  });
+
   it('encodes the update-profile variant preferences', () => {
     const buf = encodeUpdateProfile({
       displayName: 'Kaya',

ui/src/lib/codec.ts

@@ -364,9 +364,25 @@ export function decodeProfile(buf: Uint8Array): Profile {
     email: s(p.email()),
     telegramLinked: p.telegramLinked(),
     vkLinked: p.vkLinked(),
+    dictVersions: decodeDictVersions(p),
   };
 }
 
+// decodeDictVersions reads the profile's per-variant current dictionary versions into a
+// variant-keyed map, so the offline preloader can look up the version for each enabled
+// variant. An entry with an unknown variant or empty version is skipped.
+function decodeDictVersions(p: fb.Profile): Partial<Record<Variant, string>> {
+  const out: Partial<Record<Variant, string>> = {};
+  for (let i = 0; i < p.dictVersionsLength(); i++) {
+    const dv = p.dictVersions(i);
+    if (!dv) continue;
+    const variant = s(dv.variant()) as Variant;
+    const version = s(dv.version());
+    if (variant && version) out[variant] = version;
+  }
+  return out;
+}
+
 // decodeVariantPreferences reads the Profile.variant_preferences vector (the variants
 // the player enabled in Settings).
 function decodeVariantPreferences(p: fb.Profile): Variant[] {

ui/src/lib/mock/data.ts

@@ -42,6 +42,9 @@ export const PROFILE: Profile = {
   email: 'you@example.com',
   telegramLinked: false,
   vkLinked: false,
+  // Every variant's current dictionary version, as the backend advertises it on the profile —
+  // the offline preloader targets `variant@version`.
+  dictVersions: { erudit_ru: 'v1.3.0', scrabble_ru: 'v1.3.0', scrabble_en: 'v1.3.0' },
 };
 
 // Seed social/account data for the mock (pnpm start + Playwright). The mock profile

ui/src/lib/model.ts

@@ -161,6 +161,10 @@ export interface Profile {
   /** Whether a Telegram / VK identity is attached — drives the Add / Unlink controls. */
   telegramLinked: boolean;
   vkLinked: boolean;
+  /** Current dictionary version per game variant (deployment-wide, not per-account). An
+   *  offline-capable PWA reads it to preload the matching dawg for each enabled variant off
+   *  this cold-start response. Empty only in a degenerate deployment with no resident dictionary. */
+  dictVersions: Partial<Record<Variant, string>>;
 }
 
 /** Banner is the advertising-banner block of an eligible viewer's profile. */