R4: push enrichment — events carry a state delta, kill the last poll

Enrich the in-app live stream into a delta channel so the UI renders a move from the event without a follow-up game.state, and make the matchmaking poll a stream-down fallback.

- pkg/fbs: trailing fields on opponent_moved (move+game+bag_len), your_turn (move_count), match_found (state), game_over (game), notify (account/invitation/state), MoveResult (rack+bag_len); regenerate Go + TS.
- backend: notify owns the FB encoding (encode.go + payload.go input structs); game/lobby/social map their domain types in. emitMove builds the move delta; game.Service.InitialState feeds match_found/game_started the recipient's initial StateView; friends/invitations notify carry their account/invitation. The move-commit response (submit_play/pass/exchange/resign) returns the actor's refilled rack + bag size.
- gateway: MoveResult transcode carries rack+bag_len.
- ui: pure lib/gamedelta.ts reducer advances the per-game cache keyed on move_count (idempotent + gap-safe); app.svelte seeds the cache on match_found/game_started; Game.svelte applies the delta (commit/pass/exchange/resign drop their load()); NewGame polls only while app.streamAlive is false.
- docs: ARCHITECTURE §10, FUNCTIONAL(+ru), backend/gateway/ui READMEs; PRERELEASE R4 marked done + Refinements.

ui/src/gen/fbs/scrabblefb/move-result.ts

@@ -34,8 +34,28 @@ game(obj?:GameView):GameView|null {
   return offset ? (obj || new GameView()).__init(this.bb!.__indirect(this.bb_pos + offset), this.bb!) : null;
 }
 
+rack(index: number):number|null {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.readUint8(this.bb!.__vector(this.bb_pos + offset) + index) : 0;
+}
+
+rackLength():number {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.__vector_len(this.bb_pos + offset) : 0;
+}
+
+rackArray():Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? new Uint8Array(this.bb!.bytes().buffer, this.bb!.bytes().byteOffset + this.bb!.__vector(this.bb_pos + offset), this.bb!.__vector_len(this.bb_pos + offset)) : null;
+}
+
+bagLen():number {
+  const offset = this.bb!.__offset(this.bb_pos, 10);
+  return offset ? this.bb!.readInt32(this.bb_pos + offset) : 0;
+}
+
 static startMoveResult(builder:flatbuffers.Builder) {
-  builder.startObject(2);
+  builder.startObject(4);
 }
 
 static addMove(builder:flatbuffers.Builder, moveOffset:flatbuffers.Offset) {
@@ -46,6 +66,26 @@ static addGame(builder:flatbuffers.Builder, gameOffset:flatbuffers.Offset) {
   builder.addFieldOffset(1, gameOffset, 0);
 }
 
+static addRack(builder:flatbuffers.Builder, rackOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(2, rackOffset, 0);
+}
+
+static createRackVector(builder:flatbuffers.Builder, data:number[]|Uint8Array):flatbuffers.Offset {
+  builder.startVector(1, data.length, 1);
+  for (let i = data.length - 1; i >= 0; i--) {
+    builder.addInt8(data[i]!);
+  }
+  return builder.endVector();
+}
+
+static startRackVector(builder:flatbuffers.Builder, numElems:number) {
+  builder.startVector(1, numElems, 1);
+}
+
+static addBagLen(builder:flatbuffers.Builder, bagLen:number) {
+  builder.addFieldInt32(3, bagLen, 0);
+}
+
 static endMoveResult(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;