.gitea/workflows/ci.yaml

@@ -207,11 +207,66 @@ jobs:
         run: pnpm run test:e2e
         timeout-minutes: 5
 
+  # conformance proves the client's local move preview (the ported dawg reader +
+  # validator, ui/src/lib/dict) byte-for-byte against the authoritative Go engine:
+  # a Go step generates golden parity vectors from the release dictionaries, then the
+  # gated Vitest suite replays them. It spans both toolchains, so it runs whenever the
+  # Go engine side or the UI side changed.
+  conformance:
+    needs: changes
+    if: ${{ needs.changes.outputs.go == 'true' || needs.changes.outputs.ui == 'true' }}
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+    env:
+      GOPRIVATE: gitea.iliadenisov.ru/*
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Fetch dictionary DAWGs
+        run: |
+          mkdir -p "${GITHUB_WORKSPACE}/dawg"
+          curl -fsSL -o /tmp/dawg.tar.gz "https://gitea.iliadenisov.ru/developer/scrabble-dictionary/releases/download/${DICT_VERSION}/scrabble-dawg-${DICT_VERSION}.tar.gz"
+          tar xzf /tmp/dawg.tar.gz -C "${GITHUB_WORKSPACE}/dawg"
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.work
+          cache: true
+
+      - name: Generate golden parity vectors
+        run: |
+          go run ./backend/cmd/dictgen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/dictgold
+          go run ./backend/cmd/validategen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/validgold
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - name: Install pnpm
+        run: npm install -g pnpm@11.0.9
+
+      - name: Install deps
+        working-directory: ui
+        run: pnpm install --frozen-lockfile
+
+      - name: Local-eval conformance (reader + validator vs the Go engine)
+        working-directory: ui
+        env:
+          DICT_DAWG_DIR: ${{ github.workspace }}/dawg
+          DICT_GOLD_DIR: /tmp/dictgold
+          DICT_VALID_DIR: /tmp/validgold
+        run: pnpm exec vitest run src/lib/dict/
+
   # gate is the single branch-protection required check. It always runs and passes
   # only when each upstream job succeeded or was skipped (a path-filtered no-op),
   # failing the merge if any actually failed or was cancelled.
   gate:
-    needs: [unit, integration, ui]
+    needs: [unit, integration, ui, conformance]
     if: always()
     runs-on: ubuntu-latest
     defaults:
@@ -221,7 +276,7 @@ jobs:
       - name: Aggregate required checks
         run: |
           fail=
-          for r in "unit:${{ needs.unit.result }}" "integration:${{ needs.integration.result }}" "ui:${{ needs.ui.result }}"; do
+          for r in "unit:${{ needs.unit.result }}" "integration:${{ needs.integration.result }}" "ui:${{ needs.ui.result }}" "conformance:${{ needs.conformance.result }}"; do
             name="${r%%:*}"; res="${r#*:}"
             echo "$name = $res"
             case "$res" in
@@ -340,6 +395,23 @@ jobs:
           docker logs --tail 50 scrabble-backend || true
           exit 1
 
+      - name: Probe the /dict edge route reaches the gateway
+        run: |
+          set -u
+          # The client fetches each game's dictionary blob at {edge}/dict/{variant}/{version}
+          # for the local move preview. If caddy does not route /dict to the gateway the request
+          # falls to the static landing and the client silently gets a non-dawg blob. Probed
+          # unauthenticated it must be the gateway's 401 (the route reaches the gateway), never a
+          # 404/200 from the landing catch-all.
+          out="$(docker run --rm --network edge alpine:3.20 wget -S -q -O /dev/null http://scrabble/dict/scrabble_en/v1 2>&1 || true)"
+          echo "$out" | grep -E "HTTP/" || true
+          if echo "$out" | grep -q " 401"; then
+            echo "ok: /dict reaches the gateway (401 unauthenticated)"
+          else
+            echo "FAIL: /dict did not reach the gateway (expected 401) — caddy route missing?"
+            exit 1
+          fi
+
       - name: Probe the Telegram validator and bot liveness
         run: |
           set -u

backend/cmd/dictgen/main.go

@@ -0,0 +1,193 @@
+// Command dictgen dumps golden parity vectors from the committed dawg
+// dictionaries so the TypeScript dawg reader can be checked byte-for-byte
+// against the authoritative Go dafsa reader.
+//
+// For each *.dawg file it writes, into the output directory:
+//
+//   - <name>.words.bin — every stored word as alphabet-index bytes, in index
+//     order, framed as [1-byte length][length index bytes]. The word at stream
+//     position k has IndexOfB == k.
+//   - <name>.neg.bin — negative lookups (sequences whose IndexOfB is -1), same
+//     framing, to exercise the not-found path at varying depths.
+//   - <name>.meta.json — NumAdded/NumNodes/NumEdges plus the alphabet size, for
+//     a header-parse sanity cross-check on the TS side.
+//
+// It is a development tool (not built into any service), analogous to
+// cmd/jetgen. Run it from the repository root:
+//
+//	go run ./backend/cmd/dictgen -dawg-dir ../scrabble-solver/dawg -out <dir>
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	dawg "github.com/iliadenisov/dafsa"
+)
+
+// meta is the per-dictionary sanity payload cross-checked by the TS reader.
+type meta struct {
+	NumAdded int `json:"numAdded"`
+	NumNodes int `json:"numNodes"`
+	NumEdges int `json:"numEdges"`
+	Alphabet int `json:"alphabet"`
+}
+
+func main() {
+	dawgDir := flag.String("dawg-dir", "../scrabble-solver/dawg", "directory holding the .dawg files")
+	outDir := flag.String("out", "", "output directory for the golden files (required)")
+	negCount := flag.Int("neg", 20000, "number of negative lookups to emit per dictionary")
+	flag.Parse()
+
+	if *outDir == "" {
+		fail("-out is required")
+	}
+	if err := os.MkdirAll(*outDir, 0o755); err != nil {
+		fail("mkdir out: %v", err)
+	}
+
+	files, err := filepath.Glob(filepath.Join(*dawgDir, "*.dawg"))
+	if err != nil {
+		fail("glob: %v", err)
+	}
+	sort.Strings(files)
+	if len(files) == 0 {
+		fail("no .dawg files in %s", *dawgDir)
+	}
+
+	for _, f := range files {
+		if err := process(f, *outDir, *negCount); err != nil {
+			fail("%s: %v", filepath.Base(f), err)
+		}
+	}
+}
+
+// process emits the golden files for a single dawg dictionary.
+func process(path, outDir string, negCount int) error {
+	name := strings.TrimSuffix(filepath.Base(path), ".dawg")
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	finder, err := dawg.Read(bytes.NewReader(data), 0)
+	if err != nil {
+		return fmt.Errorf("read dawg: %w", err)
+	}
+	defer finder.Close()
+
+	// Stream every stored word in index order; keep a decimated sample and the
+	// maximum alphabet index for negative generation.
+	wf, err := os.Create(filepath.Join(outDir, name+".words.bin"))
+	if err != nil {
+		return err
+	}
+	bw := bufio.NewWriter(wf)
+
+	var (
+		count  int
+		maxIx  byte
+		sample [][]byte
+	)
+	finder.EnumerateB(func(index int, word []byte, final bool) int {
+		if !final {
+			return 0 // Continue
+		}
+		if index != count {
+			panic(fmt.Sprintf("%s: enumerate index gap: got %d want %d", name, index, count))
+		}
+		writeWord(bw, word)
+		for _, b := range word {
+			if b > maxIx {
+				maxIx = b
+			}
+		}
+		if count%4 == 0 && len(sample) < 60000 {
+			sample = append(sample, append([]byte(nil), word...))
+		}
+		count++
+		return 0 // Continue
+	})
+	if err := bw.Flush(); err != nil {
+		return err
+	}
+	if err := wf.Close(); err != nil {
+		return err
+	}
+	if count != finder.NumAdded() {
+		return fmt.Errorf("word count %d != NumAdded %d", count, finder.NumAdded())
+	}
+
+	alphabet := int(maxIx) + 1
+
+	// Negatives: mutate sampled real words and keep the ones the reader rejects.
+	nf, err := os.Create(filepath.Join(outDir, name+".neg.bin"))
+	if err != nil {
+		return err
+	}
+	nbw := bufio.NewWriter(nf)
+	rng := rand.New(rand.NewSource(1))
+	neg := 0
+	for neg < negCount && len(sample) > 0 {
+		base := sample[rng.Intn(len(sample))]
+		cand := append([]byte(nil), base...)
+		switch rng.Intn(3) {
+		case 0: // extend by one index
+			cand = append(cand, byte(rng.Intn(alphabet)))
+		case 1: // flip one index
+			if len(cand) > 0 {
+				cand[rng.Intn(len(cand))] = byte(rng.Intn(alphabet))
+			}
+		case 2: // drop the tail and flip the new last index
+			if len(cand) > 1 {
+				cand = cand[:len(cand)-1]
+				cand[len(cand)-1] = byte(rng.Intn(alphabet))
+			}
+		}
+		if finder.IndexOfB(cand) == -1 {
+			writeWord(nbw, cand)
+			neg++
+		}
+	}
+	if err := nbw.Flush(); err != nil {
+		return err
+	}
+	if err := nf.Close(); err != nil {
+		return err
+	}
+
+	m := meta{NumAdded: finder.NumAdded(), NumNodes: finder.NumNodes(), NumEdges: finder.NumEdges(), Alphabet: alphabet}
+	mb, err := json.MarshalIndent(m, "", "  ")
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(filepath.Join(outDir, name+".meta.json"), mb, 0o644); err != nil {
+		return err
+	}
+
+	fmt.Printf("%-12s words=%d negatives=%d alphabet=%d nodes=%d edges=%d\n",
+		name, count, neg, alphabet, finder.NumNodes(), finder.NumEdges())
+	return nil
+}
+
+// writeWord frames one index-byte word as [length][bytes].
+func writeWord(w *bufio.Writer, word []byte) {
+	if len(word) > 255 {
+		panic(fmt.Sprintf("word too long to frame: %d", len(word)))
+	}
+	w.WriteByte(byte(len(word)))
+	w.Write(word)
+}
+
+func fail(format string, args ...any) {
+	fmt.Fprintf(os.Stderr, "dictgen: "+format+"\n", args...)
+	os.Exit(1)
+}

backend/cmd/validategen/main.go

@@ -0,0 +1,486 @@
+// Command validategen produces golden conformance fixtures for the TypeScript
+// move validator (ui/src/lib/dict/validate.ts). For each variant it self-plays
+// greedy games with the authoritative scrabble-solver engine to build realistic
+// board positions, then records a battery of candidate plays — the engine's own
+// top move, letter-mutated variants, random scatters and (on the empty board) an
+// off-centre translation — each paired with the ground-truth result of
+// ValidatePlayOpts (legal, score, the words formed). The TS conformance test
+// replays these and must agree exactly.
+//
+// It is a development tool (not built into any service), analogous to
+// cmd/dictgen. Run it from the repository root:
+//
+//	go run ./backend/cmd/validategen -dawg-dir ../scrabble-solver/dawg -out <dir>
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"math/rand"
+	"os"
+	"path/filepath"
+
+	"gitea.iliadenisov.ru/developer/scrabble-solver/board"
+	"gitea.iliadenisov.ru/developer/scrabble-solver/rack"
+	"gitea.iliadenisov.ru/developer/scrabble-solver/rules"
+	"gitea.iliadenisov.ru/developer/scrabble-solver/scrabble"
+	"gitea.iliadenisov.ru/developer/scrabble-solver/selfplay"
+	dawg "github.com/iliadenisov/dafsa"
+)
+
+// blankTile marks a blank tile in a drawn hand (matches selfplay).
+const blankTile byte = 0xff
+
+// variantSpec pairs a variant label with its ruleset and dawg file.
+type variantSpec struct {
+	name  string
+	rules *rules.Ruleset
+	dawg  string
+}
+
+// cell is an occupied board square or a placement (alphabet-index letter).
+type cell struct {
+	R, C, Letter int
+	Blank        bool
+}
+
+// word mirrors scrabble.Word in index space.
+type word struct {
+	Row, Col, Dir int
+	Letters       []int
+	Blanks        []bool
+	Score         int
+}
+
+// fixture is one candidate play with the engine's ground-truth verdict.
+type fixture struct {
+	Board            int    `json:"board"` // index into the boards list
+	Dir              int    `json:"dir"`
+	IgnoreCrossWords bool   `json:"ignoreCrossWords"`
+	Tiles            []cell `json:"tiles"`
+	Legal            bool   `json:"legal"`
+	Score            int    `json:"score"`
+	Bonus            int    `json:"bonus"`
+	Main             *word  `json:"main,omitempty"`
+	Cross            []word `json:"cross,omitempty"`
+}
+
+// alphaEntry mirrors one row of the per-variant alphabet table the server sends the
+// client (index, concrete letter as the ruleset emits it, tile value), so the adapter
+// cross-test can drive the letter-space client path exactly as production does.
+type alphaEntry struct {
+	Index  int    `json:"index"`
+	Letter string `json:"letter"`
+	Value  int    `json:"value"`
+}
+
+// variantFile is the whole conformance payload for one variant.
+type variantFile struct {
+	Variant  string       `json:"variant"`
+	Rows     int          `json:"rows"`
+	Cols     int          `json:"cols"`
+	Center   int          `json:"center"`
+	RackSize int          `json:"rackSize"`
+	Bingo    int          `json:"bingo"`
+	Values   []int        `json:"values"`
+	Premiums []int        `json:"premiums"` // row-major rules.Premium codes
+	Alphabet []alphaEntry `json:"alphabet"`
+	Boards   [][]cell     `json:"boards"`
+	Fixtures []fixture    `json:"fixtures"`
+}
+
+func main() {
+	dawgDir := flag.String("dawg-dir", "../scrabble-solver/dawg", "directory holding the .dawg files")
+	outDir := flag.String("out", "", "output directory for the fixture files (required)")
+	games := flag.Int("games", 6, "self-play games per (variant, rule)")
+	plies := flag.Int("plies", 40, "maximum plies captured per game")
+	flag.Parse()
+	if *outDir == "" {
+		fail("-out is required")
+	}
+	if err := os.MkdirAll(*outDir, 0o755); err != nil {
+		fail("mkdir out: %v", err)
+	}
+
+	specs := []variantSpec{
+		{"scrabble_en", rules.English(), "en_sowpods.dawg"},
+		{"scrabble_ru", rules.RussianScrabble(), "ru_scrabble.dawg"},
+		{"erudit_ru", rules.Erudit(), "ru_erudit.dawg"},
+	}
+	for _, sp := range specs {
+		if err := generate(sp, *dawgDir, *outDir, *games, *plies); err != nil {
+			fail("%s: %v", sp.name, err)
+		}
+	}
+}
+
+func generate(sp variantSpec, dawgDir, outDir string, games, plies int) error {
+	data, err := os.ReadFile(filepath.Join(dawgDir, sp.dawg))
+	if err != nil {
+		return err
+	}
+	finder, err := dawg.Read(bytes.NewReader(data), 0)
+	if err != nil {
+		return fmt.Errorf("read dawg: %w", err)
+	}
+	defer finder.Close()
+
+	rs := sp.rules
+	solver := scrabble.NewSolver(rs, finder)
+
+	out := variantFile{
+		Variant: sp.name, Rows: rs.Rows, Cols: rs.Cols, Center: rs.Center,
+		RackSize: rs.RackSize, Bingo: rs.Bingo, Values: rs.Values,
+		Premiums: premiumCodes(rs), Alphabet: alphabetOf(rs),
+	}
+
+	// Capture under both the standard rule and the single-word rule, building the
+	// board with the same rule so positions are reachable under it.
+	for _, ignore := range []bool{false, true} {
+		opts := scrabble.PlayOptions{IgnoreCrossWords: ignore}
+		for g := range games {
+			seed := int64(g*1000) + boolseed(ignore) + variantSeed(sp.name)
+			playAndCapture(&out, rs, solver, opts, seed, plies)
+		}
+	}
+
+	b, err := json.Marshal(&out)
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(filepath.Join(outDir, sp.name+".fixtures.json"), b, 0o644); err != nil {
+		return err
+	}
+	fmt.Printf("%-12s boards=%d fixtures=%d\n", sp.name, len(out.Boards), len(out.Fixtures))
+	return nil
+}
+
+// playAndCapture greedily self-plays one game, recording candidate plays against
+// each board position along the way.
+func playAndCapture(out *variantFile, rs *rules.Ruleset, solver *scrabble.Solver, opts scrabble.PlayOptions, seed int64, plies int) {
+	rng := rand.New(rand.NewSource(seed))
+	bag := selfplay.NewBag(rs, seed)
+	b := board.New(rs.Rows, rs.Cols)
+	hands := [2][]byte{bag.Draw(rs.RackSize), bag.Draw(rs.RackSize)}
+
+	passes := 0
+	for turn := range plies {
+		p := turn % 2
+		rk := rackOf(hands[p], rs.Size())
+		moves := solver.GenerateMovesOpts(b, rk, scrabble.Both, opts)
+		if len(moves) == 0 {
+			if passes++; passes >= 4 {
+				break
+			}
+			continue
+		}
+		passes = 0
+		top := moves[0]
+
+		boardIdx := len(out.Boards)
+		out.Boards = append(out.Boards, boardCells(b))
+		captureCandidates(out, rs, solver, opts, b, boardIdx, top, rng)
+
+		scrabble.Apply(b, top)
+		hands[p] = removeUsed(hands[p], top)
+		if need := rs.RackSize - len(hands[p]); need > 0 {
+			hands[p] = append(hands[p], bag.Draw(need)...)
+		}
+		if len(hands[p]) == 0 && bag.Len() == 0 {
+			break
+		}
+	}
+}
+
+// captureCandidates records the engine's top move plus derived candidates for one
+// board, each with its ValidatePlayOpts verdict.
+func captureCandidates(out *variantFile, rs *rules.Ruleset, solver *scrabble.Solver, opts scrabble.PlayOptions, b *board.Board, boardIdx int, top scrabble.Move, rng *rand.Rand) {
+	size := rs.Size()
+	record := func(tiles []scrabble.Placement) {
+		if len(tiles) == 0 {
+			return
+		}
+		out.Fixtures = append(out.Fixtures, makeFixture(solver, opts, b, boardIdx, tiles))
+	}
+
+	// The engine's own top move (legal).
+	record(top.Tiles)
+
+	// Letter-mutated variants: usually reject on the dictionary, occasionally form
+	// a different legal word.
+	for range 3 {
+		mut := clonePlacements(top.Tiles)
+		i := rng.Intn(len(mut))
+		mut[i].Letter = byte((int(mut[i].Letter) + 1 + rng.Intn(size-1)) % size)
+		record(mut)
+	}
+
+	// Random scatters: exercise geometry, dictionary and connectivity paths.
+	for range 3 {
+		record(randomScatter(b, size, 2+rng.Intn(4), rng))
+	}
+
+	// Single tiles abutting the board exercise the direction inference — a single
+	// tile is ambiguous, its orientation resolved from which axis it extends.
+	for range 3 {
+		if t, ok := randomAdjacentSingle(b, size, rng); ok {
+			record([]scrabble.Placement{t})
+		}
+	}
+
+	// On the empty board, an off-centre translation of the first move exercises the
+	// first-move centre rule.
+	if b.IsEmpty() {
+		shifted := clonePlacements(top.Tiles)
+		ok := true
+		for i := range shifted {
+			shifted[i].Row++
+			shifted[i].Col++
+			if !b.InBounds(shifted[i].Row, shifted[i].Col) {
+				ok = false
+				break
+			}
+		}
+		if ok {
+			record(shifted)
+		}
+	}
+}
+
+// makeFixture validates a candidate against board b and serializes it with its
+// ground truth. Word breakdown is recorded only for legal plays (the TS test
+// checks words only then); an illegal play records legal=false alone.
+func makeFixture(solver *scrabble.Solver, opts scrabble.PlayOptions, b *board.Board, boardIdx int, tiles []scrabble.Placement) fixture {
+	// Infer the orientation exactly as the backend evaluate does (dir-less), so the
+	// fixture matches the real eval path and pins the client's ported inference.
+	dir := playDirectionMirror(solver, b, tiles, opts)
+	fx := fixture{
+		Board:            boardIdx,
+		Dir:              int(dir),
+		IgnoreCrossWords: opts.IgnoreCrossWords,
+		Tiles:            placementCells(tiles),
+	}
+	m, err := solver.ValidatePlayOpts(b, dir, tiles, opts)
+	if err == nil {
+		fx.Legal = true
+		fx.Score = m.Score
+		fx.Bonus = m.Bonus
+		fx.Main = toWord(m.Main)
+		for _, cw := range m.Cross {
+			fx.Cross = append(fx.Cross, *toWord(cw))
+		}
+	}
+	return fx
+}
+
+func placementCells(ts []scrabble.Placement) []cell {
+	cs := make([]cell, len(ts))
+	for i, t := range ts {
+		cs[i] = cell{R: t.Row, C: t.Col, Letter: int(t.Letter), Blank: t.Blank}
+	}
+	return cs
+}
+
+func toWord(w scrabble.Word) *word {
+	letters := make([]int, len(w.Letters))
+	for i, l := range w.Letters {
+		letters[i] = int(l)
+	}
+	return &word{
+		Row: w.Row, Col: w.Col, Dir: int(w.Dir),
+		Letters: letters, Blanks: append([]bool(nil), w.Blanks...), Score: w.Score,
+	}
+}
+
+func alphabetOf(rs *rules.Ruleset) []alphaEntry {
+	n := rs.Alphabet.Size()
+	out := make([]alphaEntry, n)
+	for i := range n {
+		ch, _ := rs.Alphabet.Character(byte(i))
+		out[i] = alphaEntry{Index: i, Letter: ch, Value: rs.Values[i]}
+	}
+	return out
+}
+
+func premiumCodes(rs *rules.Ruleset) []int {
+	codes := make([]int, rs.Rows*rs.Cols)
+	for i := range codes {
+		codes[i] = int(rs.PremiumAt(i))
+	}
+	return codes
+}
+
+func boardCells(b *board.Board) []cell {
+	var cs []cell
+	for r := 0; r < b.Rows(); r++ {
+		for c := 0; c < b.Cols(); c++ {
+			if b.Filled(r, c) {
+				v := b.At(r, c)
+				cs = append(cs, cell{R: r, C: c, Letter: int(v&0x3f) - 1, Blank: v&0x80 != 0})
+			}
+		}
+	}
+	return cs
+}
+
+func clonePlacements(ts []scrabble.Placement) []scrabble.Placement {
+	return append([]scrabble.Placement(nil), ts...)
+}
+
+// randomScatter picks n distinct empty in-bounds squares with random letters.
+func randomScatter(b *board.Board, size, n int, rng *rand.Rand) []scrabble.Placement {
+	seen := map[[2]int]bool{}
+	var ts []scrabble.Placement
+	for tries := 0; tries < n*20 && len(ts) < n; tries++ {
+		r := rng.Intn(b.Rows())
+		c := rng.Intn(b.Cols())
+		if seen[[2]int{r, c}] || b.Filled(r, c) {
+			continue
+		}
+		seen[[2]int{r, c}] = true
+		ts = append(ts, scrabble.Placement{Row: r, Col: c, Letter: byte(rng.Intn(size)), Blank: rng.Intn(10) == 0})
+	}
+	return ts
+}
+
+// randomAdjacentSingle picks a random empty in-bounds square abutting at least one
+// filled square, with a random letter — a single-tile play whose orientation the
+// inference must resolve. It returns ok=false on an empty board.
+func randomAdjacentSingle(b *board.Board, size int, rng *rand.Rand) (scrabble.Placement, bool) {
+	var cands [][2]int
+	for r := 0; r < b.Rows(); r++ {
+		for c := 0; c < b.Cols(); c++ {
+			if b.Filled(r, c) {
+				continue
+			}
+			if b.Filled(r-1, c) || b.Filled(r+1, c) || b.Filled(r, c-1) || b.Filled(r, c+1) {
+				cands = append(cands, [2]int{r, c})
+			}
+		}
+	}
+	if len(cands) == 0 {
+		return scrabble.Placement{}, false
+	}
+	rc := cands[rng.Intn(len(cands))]
+	return scrabble.Placement{Row: rc[0], Col: rc[1], Letter: byte(rng.Intn(size)), Blank: rng.Intn(10) == 0}, true
+}
+
+// playDirectionMirror mirrors engine (*Game).playDirection: the geometric
+// resolution, except a single tile under the single-word rule tries both
+// orientations through the solver and keeps the higher-scoring legal one (H wins
+// ties). It reproduces the orientation the backend evaluate infers.
+func playDirectionMirror(solver *scrabble.Solver, b *board.Board, placements []scrabble.Placement, opts scrabble.PlayOptions) scrabble.Direction {
+	geo := resolveDirectionMirror(b, placements)
+	if len(placements) != 1 || !opts.IgnoreCrossWords {
+		return geo
+	}
+	best, found, bestScore := geo, false, 0
+	for _, dir := range [...]scrabble.Direction{scrabble.Horizontal, scrabble.Vertical} {
+		m, err := solver.ValidatePlayOpts(b, dir, placements, opts)
+		if err != nil {
+			continue
+		}
+		if !found || m.Score > bestScore {
+			best, found, bestScore = dir, true, m.Score
+		}
+	}
+	return best
+}
+
+// resolveDirectionMirror mirrors engine.resolveDirection.
+func resolveDirectionMirror(b *board.Board, placements []scrabble.Placement) scrabble.Direction {
+	if len(placements) >= 2 {
+		row := placements[0].Row
+		for _, p := range placements[1:] {
+			if p.Row != row {
+				return scrabble.Vertical
+			}
+		}
+		return scrabble.Horizontal
+	}
+	if len(placements) == 1 {
+		p := placements[0]
+		h := runLengthMirror(b, p.Row, p.Col, scrabble.Horizontal)
+		v := runLengthMirror(b, p.Row, p.Col, scrabble.Vertical)
+		if v >= 2 && v > h {
+			return scrabble.Vertical
+		}
+		if h >= 2 {
+			return scrabble.Horizontal
+		}
+		if v >= 2 {
+			return scrabble.Vertical
+		}
+	}
+	return scrabble.Horizontal
+}
+
+// runLengthMirror mirrors engine.runLength.
+func runLengthMirror(b *board.Board, row, col int, dir scrabble.Direction) int {
+	dr, dc := 0, 1
+	if dir == scrabble.Vertical {
+		dr, dc = 1, 0
+	}
+	n := 1
+	for r, c := row-dr, col-dc; b.Filled(r, c); r, c = r-dr, c-dc {
+		n++
+	}
+	for r, c := row+dr, col+dc; b.Filled(r, c); r, c = r+dr, c+dc {
+		n++
+	}
+	return n
+}
+
+// rackOf builds a generation rack from a hand of tiles (reimplemented from the
+// unexported selfplay helper).
+func rackOf(tiles []byte, size int) rack.Rack {
+	r := rack.New(size)
+	for _, t := range tiles {
+		if t == blankTile {
+			r.AddBlank()
+		} else {
+			r.Add(t)
+		}
+	}
+	return r
+}
+
+// removeUsed returns the hand with the tiles consumed by m removed.
+func removeUsed(tiles []byte, m scrabble.Move) []byte {
+	out := append([]byte(nil), tiles...)
+	for _, p := range m.Tiles {
+		want := p.Letter
+		if p.Blank {
+			want = blankTile
+		}
+		for i, t := range out {
+			if t == want {
+				out = append(out[:i], out[i+1:]...)
+				break
+			}
+		}
+	}
+	return out
+}
+
+func boolseed(b bool) int64 {
+	if b {
+		return 500000
+	}
+	return 0
+}
+
+func variantSeed(name string) int64 {
+	var s int64
+	for _, r := range name {
+		s = s*131 + int64(r)
+	}
+	return s
+}
+
+func fail(format string, args ...any) {
+	fmt.Fprintf(os.Stderr, "validategen: "+format+"\n", args...)
+	os.Exit(1)
+}

backend/internal/engine/registry.go

@@ -21,11 +21,13 @@ var dictFiles = map[Variant]string{
 	VariantErudit:          "ru_erudit.dawg",
 }
 
-// entry is one resident dictionary: the loaded finder and the solver built over
-// it. The finder is retained so Close can release it.
+// entry is one resident dictionary: the loaded finder, the solver built over it
+// and the file it was loaded from. The finder is retained so Close can release
+// it; path is retained so the raw bytes can be re-read for the client download.
 type entry struct {
 	finder dawg.Finder
 	solver *scrabble.Solver
+	path   string
 }
 
 // Registry holds the dictionaries resident in memory, addressed by variant and
@@ -130,7 +132,7 @@ func (r *Registry) Load(v Variant, version, dir string) error {
 	if old, ok := r.entries[v][version]; ok {
 		_ = old.finder.Close()
 	}
-	r.entries[v][version] = entry{finder: finder, solver: scrabble.NewSolver(rs, finder)}
+	r.entries[v][version] = entry{finder: finder, solver: scrabble.NewSolver(rs, finder), path: path}
 	r.latest[v] = version
 	return nil
 }
@@ -202,6 +204,30 @@ func (r *Registry) Versions(v Variant) []string {
 	return versions
 }
 
+// DictBytes returns the raw serialized DAWG for the (variant, version) pair,
+// re-read from the file it was loaded from — the same immutable bytes the solver
+// holds. It backs the client-side dictionary download for the local move
+// preview. It returns ErrUnknownVariant or ErrUnknownVersion when that dictionary
+// is not resident, and wraps any read error. The file is read outside the lock.
+func (r *Registry) DictBytes(v Variant, version string) ([]byte, error) {
+	r.mu.RLock()
+	versions, ok := r.entries[v]
+	if !ok {
+		r.mu.RUnlock()
+		return nil, fmt.Errorf("%w: %s", ErrUnknownVariant, v)
+	}
+	e, ok := versions[version]
+	r.mu.RUnlock()
+	if !ok {
+		return nil, fmt.Errorf("%w: %s/%s", ErrUnknownVersion, v, version)
+	}
+	data, err := os.ReadFile(e.path)
+	if err != nil {
+		return nil, fmt.Errorf("engine: read %s/%s dictionary bytes from %s: %w", v, version, e.path, err)
+	}
+	return data, nil
+}
+
 // Lookup reports whether word is present in the (variant, version) dictionary,
 // backing the unlimited word-check tool. It returns ErrUnknownVariant or
 // ErrUnknownVersion when that dictionary is not resident, and an error when word

backend/internal/game/service.go

@@ -1649,6 +1649,14 @@ func (svc *Service) lookupWord(variant engine.Variant, version, word string) (bo
 	return present, nil
 }
 
+// DictBytes returns the raw serialized dictionary for the (variant, version) pair
+// from the registry, backing the client-side dictionary download used by the
+// local move preview. It surfaces engine.ErrUnknownVariant /
+// engine.ErrUnknownVersion when that dictionary is not resident.
+func (svc *Service) DictBytes(variant engine.Variant, version string) ([]byte, error) {
+	return svc.registry.DictBytes(variant, version)
+}
+
 // hintsRemaining is a player's remaining hint budget: the unspent per-game
 // allowance plus the profile wallet.
 func hintsRemaining(allowance, used, wallet int) int {

backend/internal/server/handlers.go

@@ -90,6 +90,9 @@ func (s *Server) registerRoutes() {
 		u.GET("/games/:id/draft", s.handleGetDraft)
 		u.PUT("/games/:id/draft", s.handleSaveDraft)
 		u.POST("/games/:id/hide", s.handleHideGame)
+		// Raw dictionary download for the client-side local move preview, keyed by
+		// the game's pinned (variant, version); immutable, so cached hard.
+		u.GET("/dict/:variant/:version", s.handleDictBytes)
 	}
 	if s.feedback != nil {
 		u.POST("/feedback", s.handleFeedbackSubmit)

backend/internal/server/handlers_dict.go

@@ -0,0 +1,31 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"scrabble/backend/internal/engine"
+)
+
+// handleDictBytes streams the raw serialized dictionary for a (variant, version)
+// pair so the client can validate and score moves locally — the local move
+// preview — instead of a network round trip per tile arrangement. It is reached
+// only through the gateway's session-gated /dict route (which resolves the
+// X-User-ID this group requires), and served with a long immutable cache lifetime
+// because a published dictionary version never changes. An unknown variant or a
+// version that is not resident is a 404.
+func (s *Server) handleDictBytes(c *gin.Context) {
+	variant, err := engine.ParseVariant(c.Param("variant"))
+	if err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "unknown variant"})
+		return
+	}
+	data, err := s.games.DictBytes(variant, c.Param("version"))
+	if err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "dictionary not found"})
+		return
+	}
+	c.Header("Cache-Control", "public, max-age=31536000, immutable")
+	c.Data(http.StatusOK, "application/octet-stream", data)
+}

deploy/caddy/Caddyfile

@@ -53,7 +53,7 @@
 	# The game SPA and the Connect edge are served by the gateway. Strip any
 	# client-supplied X-Scrabble-Honeypot here so the gateway only ever honours the
 	# tag the honeypot block sets below (a client cannot self-tag a real request).
-	@gateway path /app /app/* /telegram /telegram/* /vk /vk/* /scrabble.edge.v1.Gateway/*
+	@gateway path /app /app/* /telegram /telegram/* /vk /vk/* /dict/* /scrabble.edge.v1.Gateway/*
 	handle @gateway {
 		reverse_proxy gateway:8081 {
 			header_up -X-Scrabble-Honeypot

docs/ARCHITECTURE.md

@@ -352,6 +352,17 @@ Key points:
 - History is dictionary-independent (§9.1): the engine emits decoded
   `MoveRecord`s and reconstructs the board from them with `engine.ReplayBoard`
   (alphabet only, no dictionary).
+- The **client mirrors this validation path for an instant move preview** (the
+  local eval, `ui/src/lib/dict`): the dawg reader and the
+  validate/score/direction slice are ported to TypeScript, byte-for-byte against
+  this engine and pinned by the `conformance` CI job. Composing a move is scored
+  on-device with no round trip. It is an **advisory accelerator only** —
+  `submit_play` re-validates on the server, so a wrong or spoofed local result
+  cannot corrupt a game. The pinned per-game dictionary blob is fetched once
+  through a **session-gated `GET /dict/{variant}/{version}`** edge route
+  (immutable; cached in IndexedDB best-effort) and reused across sessions; any
+  miss, storage eviction or a bad-connection breaker falls back to the network
+  `evaluate`. The warm-up overlay is `docs/UI_DESIGN.md`.
 
 ## 6. Game rules
 

docs/FUNCTIONAL.md

@@ -163,7 +163,10 @@ tile that extends
 an existing word (down a column or across a row) is accepted. A play is validated
 against the game's dictionary at submit time and scored; an unlimited preview
 reports the word(s) a tentative move would form and its score, or that it is not
-legal, and the move is offered for submission only once it is confirmed legal. The dictionary check tool is
+legal, and the move is offered for submission only once it is confirmed legal. The preview is
+computed **on-device** for an instant response once the game's dictionary has loaded — a
+brief warm-up shows on the first open otherwise — and falls back to the server whenever the
+local dictionary is unavailable. The dictionary check tool is
 unlimited and offers a complaint on any result; for a word it finds, it also links out to an
 external reference dictionary (gramota.ru for Russian games, scrabblewordfinder.org for
 English) to look it up. Hints are governed per game —

docs/FUNCTIONAL_ru.md

@@ -171,7 +171,9 @@ _Вход сейчас только через провайдера, поэто
 слово (по столбцу или по строке), принимается. Ход проверяется по словарю партии при
 сдаче и считается; безлимитный предпросмотр показывает слово (или слова), которое
 образует предполагаемый ход, и его очки — либо что ход недопустим, — и ход можно
-отправить только после подтверждения, что он допустим. Инструмент проверки слова безлимитный и
+отправить только после подтверждения, что он допустим. Предпросмотр считается **на устройстве**
+и отвечает мгновенно, как только словарь партии загружен — иначе при первом открытии показывается
+короткий прогрев, — и уходит на сервер, если локальный словарь недоступен. Инструмент проверки слова безлимитный и
 предлагает пожаловаться на любой результат; для найденного слова он также даёт ссылку на
 внешний справочный словарь (gramota.ru для русских игр, scrabblewordfinder.org для английских),
 чтобы его посмотреть. Подсказки управляются настройками

docs/TESTING.md

@@ -21,6 +21,15 @@ tests or touching CI.
   mock for the friends screen (code issue/redeem, accept a request), the lobby
   invitations section, the stats screen, profile editing, and the GCG export's
   finished-only visibility.
+- **Local-eval conformance** — the client's on-device move preview (the ported
+  dawg reader + validator, `ui/src/lib/dict`) is checked byte-for-byte against the
+  authoritative Go engine. `backend/cmd/dictgen` and `backend/cmd/validategen` emit
+  golden vectors from the release dictionaries — every stored word plus a battery of
+  plays across both cross-word rules and all variants, each with the engine's
+  legality, score, words and inferred direction. The gated Vitest suites
+  (`ui/src/lib/dict/*.parity.test.ts`, skipped without their `DICT_*` env) replay
+  them and must agree exactly; the `conformance` CI job runs the whole loop, so a
+  drift in the port fails the merge.
 - **Engine** — correctness of scoring and move generation is owned
   by `scrabble-solver`'s own GCG-backed tests. `backend/internal/engine` adds, on
   top of the embedded solver: per-variant smoke tests (load all three committed

docs/UI_DESIGN.md

@@ -427,6 +427,20 @@ enabled on the first, uncached load) and flip in place when an event refreshes t
   raises a badge on the lobby ⚙️ tab (combined with the friend-request count) and a "1" on the
   Info tab.
 
+## Dictionary warm-up overlay (`components/DictWarmup.svelte`)
+
+Opening a game whose local move-preview dictionary is not yet cached shows a brief,
+non-dismissable warm-up overlay while it downloads (a returning player's cached
+dictionary loads from IndexedDB in a few ms, so the flash-guard suppresses it then).
+A darker-than-onboarding scrim covers
+the board; centred on it, a large emoji cycles through a fixed playful sequence — one
+per 500 ms tick (300 ms still, then a 200 ms clockwise spin with the current glyph
+fading out and the next fading in), looping — under a constant "Loading…" caption.
+Reduce-motion drops the spin to a plain cross-fade. A ~120 ms flash-guard suppresses
+the overlay for a disk-cached dictionary that loads in a few ms; a cold (network) load
+shows it until the dictionary is ready or a 5 s cap elapses, after which the preview
+falls back to the network. See docs/ARCHITECTURE.md §5 (the local eval).
+
 ## Caveat
 
 Emoji are rendered by the platform's system emoji font, so their exact look varies across

gateway/cmd/gateway/main.go

@@ -194,6 +194,7 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	edge := connectsrv.NewServer(connectsrv.Deps{
 		Registry:     registry,
 		Sessions:     sessions,
+		Backend:      backend,
 		Limiter:      limiter,
 		Tracker:      tracker,
 		Banlist:      banlist,

gateway/internal/backendclient/api.go

@@ -483,6 +483,13 @@ func (c *Client) Evaluate(ctx context.Context, userID, gameID string, tiles []Pl
 	return out, err
 }
 
+// DictBytes fetches the raw serialized dictionary for a (variant, version) pair,
+// backing the client-side local move preview. It returns the blob and the
+// backend's Cache-Control header, forwarded so the immutable blob is cached hard.
+func (c *Client) DictBytes(ctx context.Context, userID, variant, version string) ([]byte, string, error) {
+	return c.getRaw(ctx, "/api/v1/user/dict/"+url.PathEscape(variant)+"/"+url.PathEscape(version), userID, "Cache-Control")
+}
+
 // CheckWord looks a word up in the game's pinned dictionary. The word is carried as
 // repeated ?idx= alphabet indices; the backend echoes the decoded concrete word.
 func (c *Client) CheckWord(ctx context.Context, userID, gameID string, word []int) (WordCheckResp, error) {

gateway/internal/backendclient/client.go

@@ -125,6 +125,34 @@ func (c *Client) do(ctx context.Context, method, path, userID, clientIP string,
 	return nil
 }
 
+// getRaw performs one REST GET, returning the raw (un-decoded) response body and
+// the value of respHeader (e.g. Cache-Control). userID, when non-empty, is
+// forwarded as X-User-ID. A non-2xx response is returned as an *APIError. Unlike
+// do it does not JSON-decode, so it carries a binary payload such as a dictionary
+// blob.
+func (c *Client) getRaw(ctx context.Context, path, userID, respHeader string) ([]byte, string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
+	if err != nil {
+		return nil, "", fmt.Errorf("backendclient: new request: %w", err)
+	}
+	if userID != "" {
+		req.Header.Set("X-User-ID", userID)
+	}
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, "", fmt.Errorf("backendclient: GET %s: %w", path, err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, "", fmt.Errorf("backendclient: read response: %w", err)
+	}
+	if resp.StatusCode >= http.StatusMultipleChoices {
+		return nil, "", parseAPIError(resp.StatusCode, data)
+	}
+	return data, resp.Header.Get(respHeader), nil
+}
+
 // parseAPIError extracts the backend's {error:{code,message}} envelope.
 func parseAPIError(status int, data []byte) *APIError {
 	var env struct {

gateway/internal/connectsrv/server.go

@@ -68,6 +68,7 @@ const (
 type Server struct {
 	registry   *transcode.Registry
 	sessions   *session.Cache
+	backend    *backendclient.Client
 	limiter    *ratelimit.Limiter
 	tracker    *ratelimit.Tracker
 	banlist    *ratelimit.Banlist
@@ -91,7 +92,10 @@ type Server struct {
 type Deps struct {
 	Registry *transcode.Registry
 	Sessions *session.Cache
-	Limiter  *ratelimit.Limiter
+	// Backend is the REST client backing the session-gated /dict blob route; a nil
+	// value disables that route (it 404s).
+	Backend *backendclient.Client
+	Limiter *ratelimit.Limiter
 	// Tracker accumulates limiter rejections for the periodic report; nil
 	// selects a private tracker (rejections are then only counted, never
 	// reported).
@@ -142,6 +146,7 @@ func NewServer(d Deps) *Server {
 	return &Server{
 		registry:     d.Registry,
 		sessions:     d.Sessions,
+		backend:      d.Backend,
 		limiter:      limiter,
 		tracker:      tracker,
 		banlist:      banlist,
@@ -183,6 +188,9 @@ func (s *Server) HTTPHandler() http.Handler {
 		// does not serve the app shell at the operator path.
 		mux.Handle("/_gm/", http.NotFoundHandler())
 	}
+	// The client-side local move preview pulls each game's pinned dictionary blob
+	// through this session-gated route (not public); see dictBytesHandler.
+	mux.Handle("/dict/", s.dictBytesHandler())
 	// The embedded UI: the game SPA under /app/ (web), /telegram/ (the Telegram Mini
 	// App) and /vk/ (the VK Mini App) — the single-origin model (docs/ARCHITECTURE.md
 	// §13). All sit below the h2c wrap so the Connect edge (a more specific prefix) keeps
@@ -397,6 +405,75 @@ func (s *Server) limitAdmin(next http.Handler) http.Handler {
 	})
 }
 
+// dictBytesHandler serves the raw dictionary blob for a (variant, version) pair to
+// a signed-in client (the local move preview), proxying the backend's authed
+// endpoint. It is session-gated — not public — bounds the download with the
+// user-class limiter, and forwards the backend's immutable Cache-Control so the
+// browser caches the blob hard. Only GET is allowed; the path is
+// /dict/{variant}/{version}.
+func (s *Server) dictBytesHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if s.backend == nil {
+			http.NotFound(w, r)
+			return
+		}
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		ip := peerIP(r.RemoteAddr, r.Header)
+		if !s.limiter.Allow("user:"+ip, s.userPolicy) {
+			s.noteRateLimited(r.Context(), classUser, ip, "dict")
+			http.Error(w, "rate limited", http.StatusTooManyRequests)
+			return
+		}
+		uid, _, err := s.resolve(r.Context(), r.Header, ip)
+		if err != nil {
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+			return
+		}
+		variant, version, ok := parseDictPath(r.URL.Path)
+		if !ok {
+			http.NotFound(w, r)
+			return
+		}
+		data, cacheControl, err := s.backend.DictBytes(r.Context(), uid, variant, version)
+		if err != nil {
+			var apiErr *backendclient.APIError
+			if errors.As(err, &apiErr) && apiErr.Status < http.StatusInternalServerError {
+				http.NotFound(w, r) // unknown variant or version
+				return
+			}
+			s.log.Warn("dict fetch failed", zap.Error(err))
+			http.Error(w, "bad gateway", http.StatusBadGateway)
+			return
+		}
+		if cacheControl != "" {
+			w.Header().Set("Cache-Control", cacheControl)
+		}
+		w.Header().Set("Content-Type", "application/octet-stream")
+		_, _ = w.Write(data)
+	})
+}
+
+// parseDictPath splits /dict/{variant}/{version}; both segments must be present
+// and non-empty, and the version must not contain a further slash.
+func parseDictPath(p string) (variant, version string, ok bool) {
+	rest, found := strings.CutPrefix(p, "/dict/")
+	if !found {
+		return "", "", false
+	}
+	i := strings.IndexByte(rest, '/')
+	if i <= 0 || i == len(rest)-1 {
+		return "", "", false
+	}
+	variant, version = rest[:i], rest[i+1:]
+	if strings.Contains(version, "/") {
+		return "", "", false
+	}
+	return variant, version, true
+}
+
 // resolve extracts and resolves the Authorization bearer token to an account id
 // and its guest flag, returning a Connect Unauthenticated error when it is missing
 // or unknown.

ui/scripts/bundle-size.mjs

@@ -19,8 +19,10 @@ import { join } from 'node:path';
 
 const DIST = 'dist';
 
-// Per-chunk gzip budgets in KB.
-const BUDGET = { app: 100, shared: 30, landing: 5 };
+// Per-chunk gzip budgets in KB. The app entry was raised to 110 when the local
+// move-preview wiring landed (the heavy dict subsystem stays in lazy chunks; this
+// covers the small in-entry game/debug wiring it needs).
+const BUDGET = { app: 110, shared: 30, landing: 5 };
 
 // gzipped returns the gzipped byte size of a built asset, or 0 when the reference is not a
 // local file (e.g. the Telegram SDK loaded from a CDN) or is missing.

ui/src/components/DebugPanel.svelte

@@ -4,18 +4,39 @@
   // snapshot (no secrets, no initData values, no IP) and shares it through the OS share sheet (or a
   // clipboard copy on desktop) — a support aid for reproducing client-specific issues, e.g. the
   // Telegram Android presentation quirks. Drawn from the top, just under the app header.
+  import { onMount } from 'svelte';
   import { app, closeDebug, resetOnboarding } from '../lib/app.svelte';
   import { connection } from '../lib/connection.svelte';
   import { shareText } from '../lib/share';
   import { telegramChromeDiag } from '../lib/telegram';
 
-  const report = [
-    `app: ${__APP_VERSION__}`,
-    `locale: ${app.locale}  theme: ${app.theme}  reduceMotion: ${app.reduceMotion}`,
-    `online: ${connection.online}  streamAlive: ${app.streamAlive}`,
-    `userId: ${app.session?.userId ?? '—'}  guest: ${app.profile?.isGuest ?? '—'}`,
-    telegramChromeDiag(),
-  ].join('\n');
+  // The local move-preview snapshot — the feature flag, the bad-connection breaker and the
+  // dictionaries cached in IndexedDB with their sizes — loads async so a report about the
+  // preview is precise. Dynamically imported so the debug panel keeps the dict code lazy.
+  let dictInfo = $state('local eval: …');
+  onMount(() => {
+    void (async () => {
+      try {
+        const m = await import('../lib/dict');
+        const list = await m.listCachedDicts();
+        const cached = list.length ? list.map((d) => `${d.key}=${(d.bytes / 1024).toFixed(0)}KB`).join(' ') : 'none';
+        dictInfo = `dict breaker: ${m.dictLoadingDisabled() ? 'TRIPPED' : 'ok'}\ndicts cached: ${cached}`;
+      } catch {
+        dictInfo = 'local eval: n/a';
+      }
+    })();
+  });
+
+  const report = $derived(
+    [
+      `app: ${__APP_VERSION__}`,
+      `locale: ${app.locale}  theme: ${app.theme}  reduceMotion: ${app.reduceMotion}`,
+      `online: ${connection.online}  streamAlive: ${app.streamAlive}`,
+      `userId: ${app.session?.userId ?? '—'}  guest: ${app.profile?.isGuest ?? '—'}`,
+      telegramChromeDiag(),
+      dictInfo,
+    ].join('\n'),
+  );
 
   let label = $state('Share');
   async function share(e: MouseEvent): Promise<void> {
@@ -33,6 +54,13 @@
   function resetVisited(e: MouseEvent): void {
     e.stopPropagation();
     resetOnboarding();
+    // Also clear the local move-preview dictionary cache (safe — it re-downloads).
+    // Dynamically imported so the debug panel keeps the dict code out of the app bundle.
+    void import('../lib/dict').then((m) => {
+      m.clearDictCache();
+      m.clearDictInstances();
+      m.bustDictHttpCache(); // also bypass the browser HTTP cache on the next load (a true cold test)
+    });
     resetLabel = 'Cleared — relaunch';
     setTimeout(() => (resetLabel = 'Reset visited'), 1800);
   }

ui/src/components/DictWarmup.svelte

@@ -0,0 +1,81 @@
+<script lang="ts">
+  import { onMount, onDestroy } from 'svelte';
+  import { t } from '../lib/i18n/index.svelte';
+  import { app } from '../lib/app.svelte';
+
+  // A cute emoji cycler shown while a game's dictionary warms for the local move
+  // preview (docs/UI_DESIGN.md). One emoji per 500ms tick — 300ms static, then a
+  // 200ms clockwise spin with the current emoji fading out and the next fading in —
+  // looping through the sequence; the ten emojis span the 5s warm-up cap.
+  const EMOJIS = ['🎲', '🤔', '📡', '📀', '💾', '⏳', '🐌', '🙈', '🇷🇺', '✌️'];
+  const TICK_MS = 500;
+  const SPIN_MS = 200;
+
+  let index = $state(0);
+  let timer: ReturnType<typeof setInterval> | null = null;
+
+  onMount(() => {
+    timer = setInterval(() => (index = (index + 1) % EMOJIS.length), TICK_MS);
+  });
+  onDestroy(() => {
+    if (timer) clearInterval(timer);
+  });
+
+  // A simultaneous fade + clockwise spin used as both the in and out transition on the
+  // keyed glyph, so the outgoing and incoming emoji cross-fade in place. Under
+  // reduce-motion it degrades to a plain fade.
+  function spinFade(_node: Element, { duration = SPIN_MS }: { duration?: number } = {}) {
+    const spin = !app.reduceMotion;
+    return {
+      duration,
+      css: (u: number) => (spin ? `opacity:${u};transform:rotate(${(1 - u) * 360}deg)` : `opacity:${u}`),
+    };
+  }
+</script>
+
+<div class="overlay" role="status" aria-live="polite">
+  <div class="box">
+    <div class="stage">
+      {#key index}
+        <span class="emoji" in:spinFade out:spinFade>{EMOJIS[index]}</span>
+      {/key}
+    </div>
+    <span class="caption">{t('dict.loading')}</span>
+  </div>
+</div>
+
+<style>
+  .overlay {
+    position: fixed;
+    inset: 0;
+    z-index: 200;
+    display: grid;
+    place-items: center;
+    /* Darker than the onboarding scrim — this blocks the board until the dictionary is ready. */
+    background: rgba(0, 0, 0, 0.72);
+    padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);
+  }
+  .box {
+    display: grid;
+    justify-items: center;
+    gap: 1rem;
+  }
+  .stage {
+    display: grid;
+    place-items: center;
+    /* Reserve the glyph box so the caption never shifts as the emoji swaps. */
+    width: 4rem;
+    height: 4rem;
+  }
+  .emoji {
+    grid-area: 1 / 1;
+    font-size: 3.25rem; /* about twice a tab-bar button */
+    line-height: 1;
+    will-change: transform, opacity;
+  }
+  .caption {
+    color: #fff;
+    font-size: 1rem;
+    opacity: 0.85;
+  }
+</style>

ui/src/game/Game.svelte

@@ -4,6 +4,7 @@
   import TabBar from '../components/TabBar.svelte';
   import TapConfirm from '../components/TapConfirm.svelte';
   import Modal from '../components/Modal.svelte';
+  import DictWarmup from '../components/DictWarmup.svelte';
   import Board from './Board.svelte';
   import Rack from './Rack.svelte';
   import { gateway } from '../lib/gateway';
@@ -50,6 +51,15 @@
   let placement = $state<Placement>(newPlacement([]));
   let preview = $state<EvalResult | null>(null);
   let busy = $state(false);
+
+  // The local move-preview subsystem (dynamically imported when enabled) and the warm-up
+  // overlay state. dict is null until the subsystem loads, or when the feature is disabled.
+  let dict = $state<typeof import('../lib/dict') | null>(null);
+  let dictWarming = $state(false);
+  let warmStarted = false;
+  // Aborts the in-flight dictionary download (at the warm-up cap, or when leaving the game)
+  // so a large download does not keep starving the channel on a slow link.
+  let warmCtrl: AbortController | null = null;
   let zoomed = $state(false);
   let selected = $state<number | null>(null);
   let focus = $state<{ row: number; col: number } | null>(null);
@@ -244,6 +254,24 @@
     void load();
     void loadFriends();
     void loadBlocked();
+    // Load the local move-preview subsystem (kept out of the initial bundle) when enabled,
+    // so composing a move can be scored on-device; the network preview stays the fallback.
+    // Skipped in mock mode (no dictionary server; the mock uses the network preview path and
+    // must never see the warm-up overlay, which would intercept the e2e's taps).
+    if (import.meta.env.MODE !== 'mock') {
+      void import('../lib/dict').then((m) => {
+        dict = m;
+      });
+    }
+  });
+
+  // Warm the game's dictionary for the local move preview once, when both the game and the
+  // dynamically-imported preview subsystem are available (see warmDict).
+  $effect(() => {
+    if (dict && view && !warmStarted) {
+      warmStarted = true;
+      void warmDict();
+    }
   });
 
   // cacheSnapshot returns the open game's current state as a CachedGame for the delta reducers.
@@ -569,6 +597,10 @@
     clearReorder();
   }
   onDestroy(() => {
+    // Leaving the game: abort a still-downloading dictionary and any in-flight preview so they
+    // stop holding the channel.
+    warmCtrl?.abort();
+    evalCtrl?.abort();
     window.removeEventListener('pointermove', onWinMove);
     window.removeEventListener('pointerup', onWinUp);
     window.removeEventListener('pointerdown', onExtraPointer);
@@ -638,19 +670,74 @@
     scheduleDraftSave();
   }
 
+  // warmDict loads the game's dictionary for the local move preview when the player opens the
+  // game. When it is already cached the preview is instant and no overlay shows; a cold
+  // dictionary downloads behind a non-dismissable warm-up overlay, which hides on load or after
+  // a 5s cap — the preview then uses the network until the download finishes in the background.
+  // The bad-connection breaker skips the overlay and goes straight to the network.
+  async function warmDict() {
+    const d = dict;
+    const v = view;
+    if (!d || !v) return;
+    if (d.hasDawg(v.game.variant, v.game.dictVersion) || d.dictLoadingDisabled()) return;
+    const ctrl = new AbortController();
+    warmCtrl = ctrl;
+    let settled = false;
+    // A short flash-guard: a disk-cached dictionary loads in a few ms, so only show the
+    // overlay if the load has not settled by now — a cold (network) load always outlasts it.
+    const grace = setTimeout(() => {
+      if (!settled) dictWarming = true;
+    }, 120);
+    const loaded = await Promise.race([
+      d.getDawg(v.game.variant, v.game.dictVersion, ctrl.signal),
+      new Promise<null>((r) => setTimeout(() => r(null), 5000)),
+    ]);
+    settled = true;
+    clearTimeout(grace);
+    dictWarming = false;
+    if (!loaded) {
+      // Did not load within the cap: abort the download so it stops starving the channel this
+      // session, and count the miss toward the bad-connection breaker (3 -> stop warming).
+      ctrl.abort();
+      d.noteDictMiss();
+    }
+  }
+
   let previewTimer: ReturnType<typeof setTimeout> | null = null;
+  let evalCtrl: AbortController | null = null;
   function recompute() {
     preview = null;
     if (previewTimer) clearTimeout(previewTimer);
+    // The tiles changed: cancel any in-flight network preview (evaluate is non-mutating, so
+    // aborting is safe) — a stale, out-of-order response cannot overwrite the newer one, and
+    // rapid placements do not pile up requests on a slow link.
+    evalCtrl?.abort();
+    evalCtrl = null;
     // Off-turn the composition is position-only: no score preview or evaluate.
     if (!isMyTurn) return;
     const sub = toSubmit(placement);
     if (!sub) return;
+    // Instant on-device preview when the game's dictionary is warm; the network otherwise.
+    const d = dict;
+    const v = view;
+    if (d && v) {
+      const reader = d.peekDawg(v.game.variant, v.game.dictVersion);
+      if (reader && hasAlphabet(v.game.variant)) {
+        try {
+          preview = d.evaluateLocal(reader, v.game.variant, board, sub.tiles, v.game.multipleWordsPerTurn);
+          return;
+        } catch {
+          /* fall through to the network preview */
+        }
+      }
+    }
+    const ctrl = new AbortController();
+    evalCtrl = ctrl;
     previewTimer = setTimeout(async () => {
       try {
-        preview = await gateway.evaluate(id, sub.tiles, variant);
+        preview = await gateway.evaluate(id, sub.tiles, variant, ctrl.signal);
       } catch {
-        /* best-effort */
+        /* best-effort (or aborted) */
       }
     }, 250);
   }
@@ -1122,6 +1209,11 @@
   {/if}
 </Screen>
 
+<!-- Warm-up overlay while the game's dictionary loads for the local move preview. -->
+{#if dictWarming}
+  <DictWarmup />
+{/if}
+
 <!-- Reusable game-screen pieces, arranged differently by the portrait and landscape branches
      above so the markup and logic stay single-sourced (see the {#if landscape} split). -->
 {#snippet scoreboardBlock()}

ui/src/lib/alphabet.ts

@@ -73,6 +73,12 @@ export function valueForLetter(variant: Variant, letter: string): number {
   return i === undefined ? 0 : t.values[i];
 }
 
+/** alphabetValues returns a variant's tile values indexed by alphabet letter index, or an
+ * empty array when the table is not yet cached. The local move validator scores with it. */
+export function alphabetValues(variant: Variant): readonly number[] {
+  return cache.get(variant)?.values ?? [];
+}
+
 /** indexForLetter maps a display letter to its wire index; a blank ("?") maps to the blank
  * sentinel. It throws when the letter is outside the cached alphabet — a placement bug, not
  * user input (the UI constrains every entry point to the variant's alphabet). */

ui/src/lib/client.ts

@@ -91,12 +91,19 @@ export interface GatewayClient {
   exchange(gameId: string, tiles: string[], variant: Variant): Promise<MoveResult>;
   resign(gameId: string): Promise<MoveResult>;
   hint(gameId: string): Promise<HintResult>;
-  evaluate(gameId: string, tiles: PlacedTile[], variant: Variant): Promise<EvalResult>;
+  evaluate(gameId: string, tiles: PlacedTile[], variant: Variant, signal?: AbortSignal): Promise<EvalResult>;
   checkWord(gameId: string, word: string, variant: Variant): Promise<WordCheckResult>;
   complaint(gameId: string, word: string, note: string): Promise<void>;
   /** Hide a finished game from the caller's own lobby list; per-account, irreversible. */
   hideGame(gameId: string): Promise<void>;
 
+  // --- dictionary (local move preview) ---
+  /** Fetch the raw serialized dictionary blob for a (variant, version) pair. Session-gated;
+   *  lets the client validate and score a move locally instead of a network round trip.
+   *  opts.signal aborts a stalled download; opts.reload bypasses the browser HTTP cache (the
+   *  debug reset, for testing a cold load). */
+  fetchDict(variant: Variant, version: string, opts?: { signal?: AbortSignal; reload?: boolean }): Promise<ArrayBuffer>;
+
   // --- draft ---
   /** The player's server-persisted client-side composition (rack order + board tiles), so a
    *  reload or a second device resumes the same arrangement. The JSON is opaque to the

ui/src/lib/dict/dawg.parity.test.ts

@@ -0,0 +1,71 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync, existsSync } from 'node:fs';
+import { join } from 'node:path';
+import { Dawg } from './dawg';
+
+// Conformance gate for the ported dawg reader: it must agree with the
+// authoritative Go dafsa reader on indexOf for EVERY stored word and EVERY
+// negative, across all three shipped dictionaries. The golden vectors are
+// produced by `go run ./backend/cmd/dictgen`; point the test at them with:
+//   DICT_DAWG_DIR=<scrabble-solver>/dawg DICT_GOLD_DIR=<dictgen out>
+// When those are unset the suite skips (kept out of the default unit run until
+// a committed sample fixture lands in Phase 1).
+const dawgDir = process.env.DICT_DAWG_DIR;
+const goldDir = process.env.DICT_GOLD_DIR;
+const ready = !!dawgDir && !!goldDir && existsSync(dawgDir) && existsSync(goldDir);
+
+const names = ['en_sowpods', 'ru_scrabble', 'ru_erudit'];
+
+// eachWord walks the [1-byte length][index bytes] framing emitted by dictgen.
+function* eachWord(buf: Buffer): Generator<Uint8Array> {
+  let off = 0;
+  while (off < buf.length) {
+    const len = buf[off];
+    yield buf.subarray(off + 1, off + 1 + len);
+    off += 1 + len;
+  }
+}
+
+describe.skipIf(!ready)('dawg reader parity vs Go dafsa', () => {
+  for (const name of names) {
+    it(
+      name,
+      () => {
+        const bytes = new Uint8Array(readFileSync(join(dawgDir!, `${name}.dawg`)));
+        const meta = JSON.parse(readFileSync(join(goldDir!, `${name}.meta.json`), 'utf8'));
+        const dawg = new Dawg(bytes);
+
+        expect(dawg.numAdded).toBe(meta.numAdded);
+        expect(dawg.numNodes).toBe(meta.numNodes);
+
+        // Every stored word: indexOf(word) equals its position in index order.
+        let idx = 0;
+        let mismatches = 0;
+        const firstBad: string[] = [];
+        for (const word of eachWord(readFileSync(join(goldDir!, `${name}.words.bin`)))) {
+          const got = dawg.indexOf(word);
+          if (got !== idx) {
+            mismatches++;
+            if (firstBad.length < 5) firstBad.push(`idx ${idx}: got ${got} word [${Array.from(word)}]`);
+          }
+          idx++;
+        }
+        expect(idx).toBe(meta.numAdded);
+        expect(mismatches, firstBad.join('; ')).toBe(0);
+
+        // Negatives must resolve to -1.
+        let negMismatches = 0;
+        const firstNeg: string[] = [];
+        for (const word of eachWord(readFileSync(join(goldDir!, `${name}.neg.bin`)))) {
+          const got = dawg.indexOf(word);
+          if (got !== -1) {
+            negMismatches++;
+            if (firstNeg.length < 5) firstNeg.push(`got ${got} word [${Array.from(word)}]`);
+          }
+        }
+        expect(negMismatches, firstNeg.join('; ')).toBe(0);
+      },
+      120_000,
+    );
+  }
+});

ui/src/lib/dict/dawg.ts

@@ -0,0 +1,202 @@
+// In-memory reader for the dafsa DAWG binary format, ported byte-for-byte from
+// github.com/iliadenisov/dafsa (bits.go / disk.go / dawg.go). It answers the one
+// query the local move validator needs: given a word as alphabet-index bytes, is
+// it stored in the dictionary and at what insertion index.
+//
+// The Go reader treats the file as a big-endian, MSB-first bit stream. Every
+// field this reader touches on the lookup path is at most ~31 bits wide, so the
+// bit reader accumulates into a plain JavaScript number (no BigInt) and stays
+// exact. Faithfulness to the Go reader is enforced by dawg.parity.test.ts, which
+// checks indexOf against the authoritative Go output across the whole dictionary.
+
+// bitsLen returns the number of bits needed to represent x (Go math/bits.Len).
+function bitsLen(x: number): number {
+  return x === 0 ? 0 : 32 - Math.clz32(x);
+}
+
+/**
+ * Dawg is a read-only view over a serialized dafsa dictionary held in memory.
+ * Construct it from the raw bytes of a `.dawg` file, then call {@link indexOf}.
+ */
+export class Dawg {
+  private readonly bytes: Uint8Array;
+  private p = 0; // current position, in bits
+
+  private readonly cbits: number;
+  private readonly abits: number;
+  private readonly numEdges: number;
+  private readonly wbits: number;
+  private readonly firstNodeOffset: number;
+  private readonly hasEmptyWord: boolean;
+
+  /** Number of words stored (dafsa NumAdded). */
+  readonly numAdded: number;
+  /** Number of graph nodes (dafsa NumNodes). */
+  readonly numNodes: number;
+
+  // Scratch for the last edge resolved by getEdge, mirroring dafsa's edgeEnd +
+  // final flag. Reused to keep the lookup path allocation-free.
+  private eNode = 0;
+  private eCount = 0;
+  private eFinal = false;
+
+  constructor(bytes: Uint8Array) {
+    this.bytes = bytes;
+
+    // Reject anything that is not a serialized dawg — e.g. an HTML error page or a
+    // truncated download routed here by mistake. The 32-bit big-endian header size is
+    // the total byte length; if it does not match, the blob is not a dawg. Without
+    // this guard a non-dawg blob would parse into a bogus reader that silently reports
+    // every word as missing (so the caller must throw here to fall back to the network).
+    const declaredSize = ((bytes[0] << 24) | (bytes[1] << 16) | (bytes[2] << 8) | bytes[3]) >>> 0;
+    if (declaredSize !== bytes.length) {
+      throw new Error(`dawg: not a dawg blob (size header ${declaredSize} != ${bytes.length} bytes)`);
+    }
+
+    // Header: 32-bit size (skipped — the whole file is already in memory), then
+    // cbits, abits, the language code string, and the word/node/edge counts.
+    this.p = 32;
+    this.cbits = this.readBits(8);
+    this.abits = this.readBits(8);
+    this.skipString(); // language code — not needed to walk index bytes
+
+    const numAdded = this.readUnsigned();
+    const numNodes = this.readUnsigned();
+    this.numEdges = this.readUnsigned();
+    this.firstNodeOffset = this.p;
+    this.hasEmptyWord = this.readBits(1) === 1;
+
+    this.numAdded = numAdded;
+    this.numNodes = numNodes;
+    this.wbits = bitsLen(numAdded);
+  }
+
+  /**
+   * indexOf returns the insertion index of the given word (as alphabet-index
+   * bytes), or -1 if the word was never added. Mirrors dafsa IndexOfB.
+   */
+  indexOf(word: ArrayLike<number>): number {
+    let skipped = 0;
+    let node = 0; // rootNode
+    let final = this.hasEmptyWord;
+    for (let i = 0; i < word.length; i++) {
+      if (!this.getEdge(node, word[i])) {
+        return -1;
+      }
+      node = this.eNode;
+      final = this.eFinal;
+      skipped += this.eCount;
+    }
+    return final ? skipped : -1;
+  }
+
+  /** has reports whether the word (as alphabet-index bytes) is in the dictionary. */
+  has(word: ArrayLike<number>): boolean {
+    return this.indexOf(word) >= 0;
+  }
+
+  // getEdge resolves the outgoing edge for ch from the node at the given bit
+  // offset. On success it fills eNode/eCount/eFinal and returns true. Mirrors
+  // dafsa (*dawg).getEdge.
+  private getEdge(node: number, ch: number): boolean {
+    if (this.numEdges <= 0) {
+      return false;
+    }
+    const pos = node === 0 ? this.firstNodeOffset : node;
+    this.p = pos;
+    const nodeFinal = this.readBits(1);
+    const fallthrough = this.readBits(1);
+
+    if (fallthrough === 1) {
+      const edgeCh = this.readBits(this.cbits);
+      if (edgeCh === ch) {
+        this.eCount = nodeFinal;
+        this.eNode = this.p; // the fallthrough target is the physically next node
+        this.eFinal = this.readBits(1) === 1;
+        return true;
+      }
+      return false;
+    }
+
+    const singleEdge = this.readBits(1);
+    let numEdges = 1;
+    const nskiplen = bitsLen(this.wbits);
+    let nskip = 0;
+    if (singleEdge !== 1) {
+      numEdges = this.readUnsigned();
+      nskip = this.readBits(nskiplen);
+    }
+
+    const base = this.p; // bit offset of the first edge record
+    const recordBits = this.cbits + nskip + this.abits;
+
+    // Binary search over the edges, which are sorted ascending by character.
+    let high = numEdges;
+    let low = -1;
+    while (high - low > 1) {
+      const probe = (high + low) >> 1;
+      // The first edge omits its (zero) skip field, so every later record is
+      // shifted back by nskip bits.
+      let seekTo = base + probe * recordBits;
+      if (probe > 0) {
+        seekTo -= nskip;
+      }
+      this.p = seekTo;
+      const edgeCh = this.readBits(this.cbits);
+      const cmp = edgeCh - ch;
+      if (cmp === 0) {
+        this.eCount = probe > 0 ? this.readBits(nskip) : nodeFinal;
+        this.eNode = this.readBits(this.abits);
+        this.p = this.eNode;
+        this.eFinal = this.readBits(1) === 1;
+        return true;
+      } else if (cmp < 0) {
+        low = probe;
+      } else {
+        high = probe;
+      }
+    }
+    return false;
+  }
+
+  // readBits reads n (<= 32) bits MSB-first from the current position and
+  // advances it. Mirrors dafsa (*bitSeeker).ReadBits for the widths on this path.
+  private readBits(n: number): number {
+    let result = 0;
+    let p = this.p;
+    const bytes = this.bytes;
+    while (n > 0) {
+      const byteIndex = p >>> 3;
+      const bitInByte = p & 7;
+      const avail = 8 - bitInByte;
+      const take = avail < n ? avail : n;
+      const shift = avail - take;
+      const chunk = (bytes[byteIndex] >>> shift) & ((1 << take) - 1);
+      result = result * (1 << take) + chunk;
+      p += take;
+      n -= take;
+    }
+    this.p = p;
+    return result;
+  }
+
+  // readUnsigned reads a dafsa "7code" varint (7 payload bits per byte, high bit
+  // continues). Mirrors dafsa readUnsigned.
+  private readUnsigned(): number {
+    let result = 0;
+    for (;;) {
+      const d = this.readBits(8);
+      result = result * 128 + (d & 0x7f);
+      if ((d & 0x80) === 0) {
+        break;
+      }
+    }
+    return result;
+  }
+
+  // skipString advances past a 7code-length-prefixed byte string.
+  private skipString(): void {
+    const n = this.readUnsigned();
+    this.p += n * 8;
+  }
+}

ui/src/lib/dict/direction.ts

@@ -0,0 +1,73 @@
+// Play-direction inference, ported from the backend engine (direction.go
+// resolveDirection/runLength and domain.go (*Game).playDirection, v1.1.1). The
+// client sends tiles without an orientation; the server infers it, so the local
+// move preview must infer the same one or its words and score would diverge.
+
+import { validatePlay, Horizontal, Vertical, type Board, type Ruleset, type Placement, type Direction, type Dict } from './validate';
+
+// runLength mirrors engine.runLength: how many cells the word through (row, col)
+// along dir spans, counting the target square plus the filled runs either side.
+function runLength(b: Board, row: number, col: number, dir: Direction): number {
+  let dr = 0;
+  let dc = 1;
+  if (dir === Vertical) {
+    dr = 1;
+    dc = 0;
+  }
+  let n = 1;
+  for (let r = row - dr, c = col - dc; b.filled(r, c); r -= dr, c -= dc) n++;
+  for (let r = row + dr, c = col + dc; b.filled(r, c); r += dr, c += dc) n++;
+  return n;
+}
+
+/**
+ * resolveDirection infers a play's orientation from geometry alone, mirroring
+ * engine.resolveDirection: two or more tiles by the line they share; a single tile
+ * by the axis along which it abuts existing tiles, preferring the longer word and
+ * horizontal on a tie; a tile abutting nothing falls back to horizontal.
+ */
+export function resolveDirection(b: Board, placements: Placement[]): Direction {
+  if (placements.length >= 2) {
+    const row = placements[0].row;
+    for (let i = 1; i < placements.length; i++) {
+      if (placements[i].row !== row) return Vertical;
+    }
+    return Horizontal;
+  }
+  if (placements.length === 1) {
+    const p = placements[0];
+    const h = runLength(b, p.row, p.col, Horizontal);
+    const v = runLength(b, p.row, p.col, Vertical);
+    if (v >= 2 && v > h) return Vertical;
+    if (h >= 2) return Horizontal;
+    if (v >= 2) return Vertical;
+  }
+  return Horizontal;
+}
+
+/**
+ * playDirection resolves the orientation for a live play, mirroring engine
+ * (*Game).playDirection. It is the geometric resolution, except a single tile under
+ * the single-word rule (ignoreCrossWords) is ambiguous — its two orientations may
+ * differ in legality — so both are tried through the validator and the
+ * higher-scoring legal one is kept (horizontal breaks a tie).
+ */
+export function playDirection(b: Board, rs: Ruleset, dict: Dict, placements: Placement[]): Direction {
+  const geo = resolveDirection(b, placements);
+  if (placements.length !== 1 || !rs.ignoreCrossWords) {
+    return geo;
+  }
+  let best = geo;
+  let found = false;
+  let bestScore = 0;
+  for (const dir of [Horizontal, Vertical] as Direction[]) {
+    const r = validatePlay(b, rs, dict, dir, placements);
+    if (!r.legal || !r.move) continue;
+    if (!found || r.move.score > bestScore) {
+      best = dir;
+      found = true;
+      bestScore = r.move.score;
+    }
+  }
+  return best;
+}

ui/src/lib/dict/eval.parity.test.ts

@@ -0,0 +1,110 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync, existsSync } from 'node:fs';
+import { join } from 'node:path';
+import { Dawg } from './dawg';
+import { evaluateLocal } from './eval';
+import { setAlphabet } from '../alphabet';
+import type { Board as ClientBoard, BoardCell } from '../board';
+import type { PlacedTile } from '../client';
+import type { Variant } from '../model';
+
+// End-to-end conformance for the local-eval ADAPTER: it drives evaluateLocal through
+// the real letter-space client path (the server-sent alphabet table, a letter board,
+// letter placements) and asserts it matches the Go engine's EvalResult for every
+// fixture. This is the cross-test the algorithm-level validate.parity suite does not
+// cover — it exercises the letter<->index mapping, the ruleset assembly and the word
+// decode, not just the index-space validator. Env-gated like the other parity suites.
+const dawgDir = process.env.DICT_DAWG_DIR;
+const validDir = process.env.DICT_VALID_DIR;
+const ready = !!dawgDir && !!validDir && existsSync(dawgDir) && existsSync(validDir);
+
+const dawgFile: Record<string, string> = {
+  scrabble_en: 'en_sowpods.dawg',
+  scrabble_ru: 'ru_scrabble.dawg',
+  erudit_ru: 'ru_erudit.dawg',
+};
+
+interface FxCell {
+  R: number;
+  C: number;
+  Letter: number;
+  Blank: boolean;
+}
+interface FxWord {
+  Letters: number[];
+}
+interface Fx {
+  board: number;
+  ignoreCrossWords: boolean;
+  tiles: FxCell[];
+  legal: boolean;
+  score: number;
+  main?: FxWord;
+  cross?: FxWord[];
+}
+interface Alpha {
+  index: number;
+  letter: string;
+  value: number;
+}
+interface VF {
+  rows: number;
+  cols: number;
+  alphabet: Alpha[];
+  boards: (FxCell[] | null)[];
+  fixtures: Fx[];
+}
+
+describe.skipIf(!ready)('local-eval adapter parity vs Go engine', () => {
+  for (const variant of Object.keys(dawgFile)) {
+    it(
+      variant,
+      () => {
+        const vf: VF = JSON.parse(readFileSync(join(validDir!, `${variant}.fixtures.json`), 'utf8'));
+        const dawg = new Dawg(new Uint8Array(readFileSync(join(dawgDir!, dawgFile[variant]))));
+        const v = variant as Variant;
+
+        // Seed the alphabet cache exactly as the server would (wire entries, lower-cased
+        // letters); the adapter re-encodes through it, just like production.
+        setAlphabet(v, vf.alphabet.map((a) => ({ index: a.index, letter: a.letter, value: a.value })));
+        const upper = vf.alphabet.map((a) => a.letter.toUpperCase());
+        const lower = vf.alphabet.map((a) => a.letter);
+
+        let legalCount = 0;
+        let mismatches = 0;
+        const first: string[] = [];
+
+        for (let fi = 0; fi < vf.fixtures.length; fi++) {
+          const fx = vf.fixtures[fi];
+
+          // Build the client's letter-space board and placements from the fixture.
+          const board: ClientBoard = Array.from({ length: vf.rows }, () =>
+            Array.from({ length: vf.cols }, () => null as BoardCell | null),
+          );
+          for (const cl of vf.boards[fx.board] ?? []) board[cl.R][cl.C] = { letter: upper[cl.Letter], blank: cl.Blank };
+          const tiles: PlacedTile[] = fx.tiles.map((t) => ({ row: t.R, col: t.C, letter: upper[t.Letter], blank: t.Blank }));
+
+          const res = evaluateLocal(dawg, v, board, tiles, !fx.ignoreCrossWords);
+
+          if (fx.legal) legalCount++;
+
+          let ok = res.legal === fx.legal;
+          if (ok && fx.legal) {
+            const wantWords = [fx.main!, ...(fx.cross ?? [])].map((w) => w.Letters.map((i) => lower[i]).join(''));
+            ok = res.score === fx.score && res.words.length === wantWords.length && res.words.every((w, i) => w === wantWords[i]);
+          }
+          if (!ok) {
+            mismatches++;
+            if (first.length < 8) {
+              first.push(`#${fi} exp legal=${fx.legal} score=${fx.score} got legal=${res.legal} score=${res.score} words=${JSON.stringify(res.words)}`);
+            }
+          }
+        }
+
+        expect(legalCount, 'fixtures should include legal plays').toBeGreaterThan(0);
+        expect(mismatches, first.join(' | ')).toBe(0);
+      },
+      120_000,
+    );
+  }
+});

ui/src/lib/dict/eval.ts

@@ -0,0 +1,104 @@
+// The local move preview: it produces the same EvalResult the network `evaluate`
+// returns (legality, score, the words formed, the inferred orientation), computed
+// on-device from a loaded dictionary so composing a move needs no round trip. It
+// adapts the client's letter-space board and placements into the validator's
+// index space (lib/dict/validate.ts), assembling the per-variant ruleset from the
+// static geometry/constants (lib/premiums.ts) and the server-sent tile values
+// (lib/alphabet.ts). The server stays authoritative — submit re-validates — so any
+// throw here is caught by the caller, which falls back to the network preview.
+
+import { validatePlay, Horizontal, type Board as VBoard, type Ruleset, type Placement as VPlacement, type Dict } from './validate';
+import { playDirection } from './direction';
+import type { Board as ClientBoard } from '../board';
+import type { PlacedTile } from '../client';
+import type { EvalResult, Variant } from '../model';
+import { premiumGrid, centre, BOARD_SIZE, RACK_SIZE, BINGO, type Premium } from '../premiums';
+import { alphabetValues, indexForLetter, letterForIndex } from '../alphabet';
+
+function letterMultOf(p: Premium): number {
+  return p === 'DL' ? 2 : p === 'TL' ? 3 : 1;
+}
+function wordMultOf(p: Premium): number {
+  return p === 'DW' ? 2 : p === 'TW' ? 3 : 1;
+}
+
+// buildBoard adapts the client's letter-space board into the validator's
+// index-space read view, precomputing the letter indices once.
+function buildBoard(variant: Variant, board: ClientBoard): VBoard {
+  const grid: ({ letter: number; blank: boolean } | null)[] = new Array(BOARD_SIZE * BOARD_SIZE).fill(null);
+  let empty = true;
+  for (let r = 0; r < BOARD_SIZE; r++) {
+    for (let c = 0; c < BOARD_SIZE; c++) {
+      const cell = board[r][c];
+      if (cell) {
+        grid[r * BOARD_SIZE + c] = { letter: indexForLetter(variant, cell.letter), blank: cell.blank };
+        empty = false;
+      }
+    }
+  }
+  const inBounds = (r: number, c: number): boolean => r >= 0 && r < BOARD_SIZE && c >= 0 && c < BOARD_SIZE;
+  return {
+    inBounds,
+    filled: (r, c) => inBounds(r, c) && grid[r * BOARD_SIZE + c] !== null,
+    cellAt: (r, c) => grid[r * BOARD_SIZE + c]!,
+    isEmpty: () => empty,
+  };
+}
+
+// buildRuleset assembles the per-variant scoring rules the validator needs.
+function buildRuleset(variant: Variant, multipleWords: boolean): Ruleset {
+  const prem = premiumGrid(variant);
+  const ctr = centre(variant);
+  const values = alphabetValues(variant);
+  return {
+    cols: BOARD_SIZE,
+    center: ctr.row * BOARD_SIZE + ctr.col,
+    rackSize: RACK_SIZE,
+    bingo: BINGO[variant],
+    values,
+    letterMult: (r, c) => letterMultOf(prem[r][c]),
+    wordMult: (r, c) => wordMultOf(prem[r][c]),
+    ignoreCrossWords: !multipleWords,
+  };
+}
+
+// decodeWord turns a word's alphabet indices back into a lower-cased string, the
+// form the network EvalResult carries (the caption renders it directly).
+function decodeWord(variant: Variant, letters: number[]): string {
+  let s = '';
+  for (const i of letters) s += letterForIndex(variant, i);
+  return s.toLowerCase();
+}
+
+/**
+ * evaluateLocal computes the move preview for tiles placed on board in the given
+ * game, returning the same shape as the network `evaluate`. dict is the loaded
+ * dictionary reader for the game's (variant, version); multipleWords is the game's
+ * cross-word rule. It may throw if the variant's alphabet table is not loaded — the
+ * caller guards with hasAlphabet and falls back to the network on any failure.
+ */
+export function evaluateLocal(
+  dict: Dict,
+  variant: Variant,
+  board: ClientBoard,
+  tiles: PlacedTile[],
+  multipleWords: boolean,
+): EvalResult {
+  const vboard = buildBoard(variant, board);
+  const rs = buildRuleset(variant, multipleWords);
+  const vtiles: VPlacement[] = tiles.map((t) => ({
+    row: t.row,
+    col: t.col,
+    letter: indexForLetter(variant, t.letter),
+    blank: t.blank,
+  }));
+
+  const dir = playDirection(vboard, rs, dict, vtiles);
+  const res = validatePlay(vboard, rs, dict, dir, vtiles);
+  if (!res.legal || !res.move) {
+    return { legal: false, score: 0, words: [], dir: '' };
+  }
+  const m = res.move;
+  const words = [m.main, ...m.cross].map((w) => decodeWord(variant, w.letters));
+  return { legal: true, score: m.score, words, dir: dir === Horizontal ? 'H' : 'V' };
+}

ui/src/lib/dict/index.ts

@@ -0,0 +1,7 @@
+// Public surface of the local move-preview subsystem, imported dynamically by the
+// game so the whole dict subsystem (the reader, the validator, the cache) stays out
+// of the initial app bundle — it is a progressive enhancement over the network
+// preview, which remains the fallback.
+export { evaluateLocal } from './eval';
+export { getDawg, peekDawg, hasDawg, dictLoadingDisabled, noteDictMiss, clearDictInstances, bustDictHttpCache } from './loader';
+export { clearDictCache, listCachedDicts } from './store';

ui/src/lib/dict/loader.ts

@@ -0,0 +1,136 @@
+// Loads the dictionary reader for a (variant, version) pair for the local move
+// preview, three tiers deep: an in-memory reader instance, then the persistent
+// IndexedDB blob cache, then a session-gated network fetch (which repopulates the
+// cache). Every tier is best-effort: on any failure getDawg resolves to null and
+// the caller falls back to the network `evaluate`. Concurrent requests for the
+// same dictionary share one in-flight load.
+
+import { Dawg } from './dawg';
+import { dictKey, idbGetDawg, idbPutDawg, idbDelDawg, requestPersist } from './store';
+import { gateway } from '../gateway';
+import type { Variant } from '../model';
+
+// Loaded readers by key. A dictionary is immutable, so an instance is reused for
+// the whole app session once loaded.
+const instances = new Map<string, Dawg>();
+// In-flight loads by key, so overlapping callers (prefetch + a game open) share one.
+const inflight = new Map<string, Promise<Dawg | null>>();
+
+// Bad-connection breaker: after a few dictionaries fail to become available in a session
+// (a load that failed or a warm-up that hit its cap), stop attempting them so the player
+// is not stuck re-watching the warm-up overlay when switching games. Session-scoped (in
+// memory) — an app relaunch is a natural retry, when the connection may have recovered.
+// Cached dictionaries still load.
+const MISS_LIMIT = 3;
+let misses = 0;
+let dictDisabled = false;
+
+/**
+ * noteDictMiss records that a dictionary did not become available in time — a load that
+ * failed or a warm-up that hit its cap. After MISS_LIMIT in a session the breaker trips.
+ */
+export function noteDictMiss(): void {
+  if (!dictDisabled && ++misses >= MISS_LIMIT) dictDisabled = true;
+}
+
+/** dictLoadingDisabled reports whether the bad-connection breaker has tripped for this
+ *  session, so callers can skip the warm-up overlay and go straight to the network. */
+export function dictLoadingDisabled(): boolean {
+  return dictDisabled;
+}
+
+// One-shot: the debug reset sets this so the next network fetch bypasses the browser HTTP
+// cache. The immutable dict blob is otherwise cached for a year, so clearing IndexedDB alone
+// still reloads it instantly from the HTTP cache — this forces a genuinely cold load.
+let bustNext = false;
+
+/** bustDictHttpCache makes the next dictionary download bypass the browser HTTP cache. */
+export function bustDictHttpCache(): void {
+  bustNext = true;
+}
+
+/**
+ * getDawg resolves the reader for the (variant, version) dictionary, or null when
+ * it cannot be obtained (no session, offline, storage or decode failure) — the
+ * caller then previews over the network instead. Successful loads are cached in
+ * memory and, when freshly fetched, in IndexedDB.
+ */
+export function getDawg(variant: Variant, version: string, signal?: AbortSignal): Promise<Dawg | null> {
+  const key = dictKey(variant, version);
+  const have = instances.get(key);
+  if (have) return Promise.resolve(have);
+  const pending = inflight.get(key);
+  if (pending) return pending;
+  const p = load(variant, version, key, signal).finally(() => inflight.delete(key));
+  inflight.set(key, p);
+  return p;
+}
+
+async function load(variant: Variant, version: string, key: string, signal?: AbortSignal): Promise<Dawg | null> {
+  // Tier 1: the persistent cache.
+  try {
+    const cached = await idbGetDawg(key);
+    if (cached) {
+      const reader = new Dawg(new Uint8Array(cached));
+      instances.set(key, reader);
+      return reader;
+    }
+  } catch {
+    // A cached blob the reader rejected (a stale or partial entry): evict it so the next
+    // load re-fetches instead of failing on it forever, then fall through to the network.
+    void idbDelDawg(key);
+  }
+
+  // Tier 2: the session-gated download — gated by the bad-connection breaker. A caller's
+  // signal aborts it (the warm-up giving up at its cap, or the game being left) so a large
+  // download does not keep starving the channel on a slow link; the caller counts the miss.
+  if (dictDisabled) return null;
+  let buf: ArrayBuffer;
+  const reload = bustNext;
+  bustNext = false;
+  try {
+    buf = await gateway.fetchDict(variant, version, { signal, reload });
+  } catch {
+    return null; // network error or aborted
+  }
+
+  let reader: Dawg;
+  try {
+    reader = new Dawg(new Uint8Array(buf));
+  } catch {
+    return null; // not a dawg — do not cache it
+  }
+  instances.set(key, reader);
+  void idbPutDawg(key, buf);
+  void requestPersist();
+  return reader;
+}
+
+/**
+ * hasDawg reports whether the (variant, version) reader is already loaded in
+ * memory (a warm hit), so the UI can decide instantly whether to preview locally
+ * or show the warm-up state while the dictionary loads.
+ */
+export function hasDawg(variant: Variant, version: string): boolean {
+  return instances.has(dictKey(variant, version));
+}
+
+/**
+ * peekDawg returns the already-loaded reader for (variant, version), or null. It is
+ * a synchronous in-memory lookup (no load), so the move preview can validate locally
+ * without awaiting when the dictionary is already warm.
+ */
+export function peekDawg(variant: Variant, version: string): Dawg | null {
+  return instances.get(dictKey(variant, version)) ?? null;
+}
+
+/**
+ * clearDictInstances drops the in-memory readers (e.g. on logout). The persistent
+ * IndexedDB cache is left intact — a dictionary version is immutable and reusable
+ * by the next account on the device.
+ */
+export function clearDictInstances(): void {
+  instances.clear();
+  misses = 0;
+  dictDisabled = false;
+}

ui/src/lib/dict/store.ts

@@ -0,0 +1,154 @@
+// Persistent cache for dictionary DAWG blobs, keyed by `${variant}@${version}`.
+// It lives in its own IndexedDB database, separate from session.ts's 'scrabble'
+// DB, so the multi-hundred-KB binary blobs never interfere with the session /
+// prefs store or its schema versioning. Everything here is best-effort: any
+// failure resolves to a miss or a no-op and the caller falls back to the network.
+
+const DB_NAME = 'scrabble-dict';
+const STORE = 'dawg';
+
+let dbPromise: Promise<IDBDatabase> | null | undefined;
+
+function openDb(): Promise<IDBDatabase> | null {
+  if (dbPromise !== undefined) return dbPromise;
+  if (typeof indexedDB === 'undefined') {
+    dbPromise = null;
+    return null;
+  }
+  dbPromise = new Promise<IDBDatabase>((resolve, reject) => {
+    const req = indexedDB.open(DB_NAME, 1);
+    req.onupgradeneeded = () => req.result.createObjectStore(STORE);
+    req.onsuccess = () => resolve(req.result);
+    req.onerror = () => reject(req.error);
+  }).catch(() => {
+    dbPromise = null;
+    throw new Error('indexedDB unavailable');
+  });
+  return dbPromise;
+}
+
+/** dictKey is the persistent cache key for a (variant, version) dictionary. */
+export function dictKey(variant: string, version: string): string {
+  return `${variant}@${version}`;
+}
+
+/** idbGetDawg returns the cached blob for key, or null on a miss or any failure. */
+export async function idbGetDawg(key: string): Promise<ArrayBuffer | null> {
+  const db = openDb();
+  if (!db) return null;
+  try {
+    const d = await db;
+    return await new Promise<ArrayBuffer | null>((resolve, reject) => {
+      const r = d.transaction(STORE, 'readonly').objectStore(STORE).get(key);
+      r.onsuccess = () => resolve((r.result ?? null) as ArrayBuffer | null);
+      r.onerror = () => reject(r.error);
+    });
+  } catch {
+    return null;
+  }
+}
+
+/** idbPutDawg stores the blob under key, swallowing any failure (best-effort). */
+export async function idbPutDawg(key: string, data: ArrayBuffer): Promise<void> {
+  const db = openDb();
+  if (!db) return;
+  try {
+    const d = await db;
+    await new Promise<void>((resolve, reject) => {
+      const tx = d.transaction(STORE, 'readwrite');
+      tx.objectStore(STORE).put(data, key);
+      tx.oncomplete = () => resolve();
+      tx.onerror = () => reject(tx.error);
+    });
+  } catch {
+    /* best-effort: a failed persist just re-downloads next time */
+  }
+}
+
+/** idbDelDawg removes a cached blob — e.g. a stale or partial entry the reader rejected, so
+ *  the next load re-fetches instead of failing on it forever. Best-effort. */
+export async function idbDelDawg(key: string): Promise<void> {
+  const db = openDb();
+  if (!db) return;
+  try {
+    const d = await db;
+    await new Promise<void>((resolve) => {
+      const tx = d.transaction(STORE, 'readwrite');
+      tx.objectStore(STORE).delete(key);
+      tx.oncomplete = () => resolve();
+      tx.onerror = () => resolve();
+    });
+  } catch {
+    /* best-effort */
+  }
+}
+
+let persistRequested = false;
+
+/**
+ * requestPersist asks the browser (once) not to evict this origin's storage, so a
+ * cached dictionary survives storage pressure. The grant is honoured unevenly
+ * across platforms (see docs), so it is only a hint — the cache stays best-effort.
+ */
+export async function requestPersist(): Promise<void> {
+  if (persistRequested) return;
+  persistRequested = true;
+  try {
+    if (typeof navigator !== 'undefined' && navigator.storage?.persist) {
+      await navigator.storage.persist();
+    }
+  } catch {
+    /* ignore — persistence is only a hint */
+  }
+}
+
+/**
+ * listCachedDicts returns the key (variant@version) and byte length of every cached
+ * dictionary blob, for the debug panel's local-dictionary readout. Best-effort: an
+ * empty list on any failure.
+ */
+export async function listCachedDicts(): Promise<Array<{ key: string; bytes: number }>> {
+  const db = openDb();
+  if (!db) return [];
+  try {
+    const d = await db;
+    return await new Promise((resolve) => {
+      const out: Array<{ key: string; bytes: number }> = [];
+      const req = d.transaction(STORE, 'readonly').objectStore(STORE).openCursor();
+      req.onsuccess = () => {
+        const cur = req.result;
+        if (!cur) {
+          resolve(out);
+          return;
+        }
+        const v = cur.value as ArrayBuffer;
+        out.push({ key: String(cur.key), bytes: v?.byteLength ?? 0 });
+        cur.continue();
+      };
+      req.onerror = () => resolve(out);
+    });
+  } catch {
+    return [];
+  }
+}
+
+/**
+ * clearDictCache empties the dictionary blob store (backs the DebugPanel reset). The
+ * store is cleared rather than the database deleted, to avoid a delete blocked on an
+ * open handle. Best-effort: a failure just leaves the cache to be reused.
+ */
+export async function clearDictCache(): Promise<void> {
+  const db = openDb();
+  if (!db) return;
+  try {
+    const d = await db;
+    await new Promise<void>((resolve, reject) => {
+      const tx = d.transaction(STORE, 'readwrite');
+      tx.objectStore(STORE).clear();
+      tx.oncomplete = () => resolve();
+      tx.onerror = () => reject(tx.error);
+    });
+  } catch {
+    /* best-effort */
+  }
+}

ui/src/lib/dict/validate.parity.test.ts

@@ -0,0 +1,163 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync, existsSync } from 'node:fs';
+import { join } from 'node:path';
+import { Dawg } from './dawg';
+import { validatePlay, type Board, type Ruleset, type Placement, type Cell, type Direction } from './validate';
+import { playDirection } from './direction';
+import { premiumGrid, centre, BINGO, RACK_SIZE, BOARD_SIZE } from '../premiums';
+import type { Variant } from '../model';
+
+// Conformance gate for the ported validator: for every fixture produced by
+// `go run ./backend/cmd/validategen`, validatePlay must agree with the Go engine
+// on legality, and — when legal — on the score, the bonus and the exact words
+// formed (main + cross), across all variants and both cross-word rules. Point it
+// at the fixtures + dictionaries with:
+//   DICT_DAWG_DIR=<scrabble-solver>/dawg DICT_VALID_DIR=<validategen out>
+// It skips when those are unset (kept out of the default unit run until a
+// committed sample fixture lands).
+const dawgDir = process.env.DICT_DAWG_DIR;
+const validDir = process.env.DICT_VALID_DIR;
+const ready = !!dawgDir && !!validDir && existsSync(dawgDir) && existsSync(validDir);
+
+const dawgFile: Record<string, string> = {
+  scrabble_en: 'en_sowpods.dawg',
+  scrabble_ru: 'ru_scrabble.dawg',
+  erudit_ru: 'ru_erudit.dawg',
+};
+
+interface FxCell {
+  R: number;
+  C: number;
+  Letter: number;
+  Blank: boolean;
+}
+interface FxWord {
+  Letters: number[];
+  Score: number;
+}
+interface Fx {
+  board: number;
+  dir: number;
+  ignoreCrossWords: boolean;
+  tiles: FxCell[];
+  legal: boolean;
+  score: number;
+  bonus: number;
+  main?: FxWord;
+  cross?: FxWord[];
+}
+interface VF {
+  rows: number;
+  cols: number;
+  center: number;
+  rackSize: number;
+  bingo: number;
+  values: number[];
+  premiums: number[];
+  boards: (FxCell[] | null)[];
+  fixtures: Fx[];
+}
+
+// Mirror rules.Premium.LetterMult / WordMult over the premium codes
+// (0 none, 1 DL, 2 TL, 3 DW, 4 TW) emitted by validategen.
+const letterMultOf = (code: number): number => (code === 1 ? 2 : code === 2 ? 3 : 1);
+const wordMultOf = (code: number): number => (code === 3 ? 2 : code === 4 ? 3 : 1);
+
+function makeBoard(rows: number, cols: number, cells: FxCell[]): Board {
+  const grid: (Cell | null)[] = new Array(rows * cols).fill(null);
+  for (const cl of cells) grid[cl.R * cols + cl.C] = { letter: cl.Letter, blank: cl.Blank };
+  const inBounds = (r: number, c: number) => r >= 0 && r < rows && c >= 0 && c < cols;
+  return {
+    inBounds,
+    filled: (r, c) => inBounds(r, c) && grid[r * cols + c] !== null,
+    cellAt: (r, c) => grid[r * cols + c] as Cell,
+    isEmpty: () => cells.length === 0,
+  };
+}
+
+function arrEq(a: number[], b: number[]): boolean {
+  if (a.length !== b.length) return false;
+  for (let i = 0; i < a.length; i++) if (a[i] !== b[i]) return false;
+  return true;
+}
+
+describe.skipIf(!ready)('validator parity vs Go engine', () => {
+  for (const variant of Object.keys(dawgFile)) {
+    it(
+      variant,
+      () => {
+        const vf: VF = JSON.parse(readFileSync(join(validDir!, `${variant}.fixtures.json`), 'utf8'));
+        const dawg = new Dawg(new Uint8Array(readFileSync(join(dawgDir!, dawgFile[variant]))));
+        const v = variant as Variant;
+
+        // Pin the client's static per-variant rule constants to the engine's ruleset.
+        expect(RACK_SIZE, 'rack size').toBe(vf.rackSize);
+        expect(BINGO[v], 'bingo').toBe(vf.bingo);
+        const ctr = centre(v);
+        expect(ctr.row * BOARD_SIZE + ctr.col, 'centre').toBe(vf.center);
+        const clientPrem = premiumGrid(v);
+        const premCode = (p: string): number => (p === 'DL' ? 1 : p === 'TL' ? 2 : p === 'DW' ? 3 : p === 'TW' ? 4 : 0);
+        let premOk = true;
+        for (let r = 0; r < vf.rows; r++)
+          for (let c = 0; c < vf.cols; c++) if (premCode(clientPrem[r][c]) !== vf.premiums[r * vf.cols + c]) premOk = false;
+        expect(premOk, 'premium grid matches engine').toBe(true);
+
+        let legalCount = 0;
+        let illegalCount = 0;
+        let mismatches = 0;
+        let dirMismatches = 0;
+        const first: string[] = [];
+        const firstDir: string[] = [];
+
+        for (let fi = 0; fi < vf.fixtures.length; fi++) {
+          const fx = vf.fixtures[fi];
+          const board = makeBoard(vf.rows, vf.cols, vf.boards[fx.board] ?? []);
+          const rs: Ruleset = {
+            cols: vf.cols,
+            center: vf.center,
+            rackSize: vf.rackSize,
+            bingo: vf.bingo,
+            values: vf.values,
+            letterMult: (r, c) => letterMultOf(vf.premiums[r * vf.cols + c]),
+            wordMult: (r, c) => wordMultOf(vf.premiums[r * vf.cols + c]),
+            ignoreCrossWords: fx.ignoreCrossWords,
+          };
+          const tiles: Placement[] = fx.tiles.map((t) => ({ row: t.R, col: t.C, letter: t.Letter, blank: t.Blank }));
+          const res = validatePlay(board, rs, dawg, fx.dir as Direction, tiles);
+
+          const gotDir = playDirection(board, rs, dawg, tiles);
+          if (gotDir !== fx.dir) {
+            dirMismatches++;
+            if (firstDir.length < 8) firstDir.push(`#${fi} dir exp ${fx.dir} got ${gotDir}`);
+          }
+
+          if (fx.legal) legalCount++;
+          else illegalCount++;
+
+          let ok = res.legal === fx.legal;
+          if (ok && fx.legal) {
+            const m = res.move!;
+            ok =
+              m.score === fx.score &&
+              m.bonus === fx.bonus &&
+              arrEq(m.main.letters, fx.main!.Letters) &&
+              m.cross.length === (fx.cross?.length ?? 0) &&
+              m.cross.every((w, i) => arrEq(w.letters, fx.cross![i].Letters));
+          }
+          if (!ok) {
+            mismatches++;
+            if (first.length < 8) {
+              first.push(`#${fi} exp legal=${fx.legal} score=${fx.score} got legal=${res.legal} score=${res.move?.score ?? '-'}`);
+            }
+          }
+        }
+
+        expect(legalCount, 'fixtures should include legal plays').toBeGreaterThan(0);
+        expect(illegalCount, 'fixtures should include illegal plays').toBeGreaterThan(0);
+        expect(mismatches, first.join(' | ')).toBe(0);
+        expect(dirMismatches, firstDir.join(' | ')).toBe(0);
+      },
+      120_000,
+    );
+  }
+});

ui/src/lib/dict/validate.ts

@@ -0,0 +1,338 @@
+// Local move validator + scorer, ported from the scrabble-solver engine
+// (scrabble/score.go and scrabble/solver.go, v1.1.1). It answers exactly what the
+// server `evaluate` endpoint answers — is a play legal, what words does it form,
+// and for how many points — so the client can preview a move without a round
+// trip. The server stays authoritative: `submit_play` re-validates on commit, so
+// this is an advisory accelerator, never a source of truth.
+//
+// Everything here works in alphabet-index space, mirroring the Go engine. The
+// caller adapts the client's board/placements (letters) into indices via
+// lib/alphabet.ts and the premium geometry via lib/premiums.ts. Faithfulness to
+// the Go engine is pinned by validate.parity.test.ts against golden fixtures.
+
+/** Horizontal is an across play (fixed row, axis along columns). Mirrors scrabble.Horizontal. */
+export const Horizontal = 0;
+/** Vertical is a down play (fixed column, axis along rows). Mirrors scrabble.Vertical. */
+export const Vertical = 1;
+export type Direction = typeof Horizontal | typeof Vertical;
+
+/** A single newly-placed tile (alphabet-index letter; blank scores 0). */
+export interface Placement {
+  row: number;
+  col: number;
+  letter: number;
+  blank: boolean;
+}
+
+/** An occupied board square: an alphabet-index letter and whether it is a blank. */
+export interface Cell {
+  letter: number;
+  blank: boolean;
+}
+
+/**
+ * Board is the minimal read view the validator needs over the current position.
+ * cellAt is only consulted for squares that filled() reports as occupied.
+ */
+export interface Board {
+  inBounds(row: number, col: number): boolean;
+  /** filled reports whether (row, col) is on the board AND occupied. */
+  filled(row: number, col: number): boolean;
+  cellAt(row: number, col: number): Cell;
+  /** isEmpty reports whether the whole board is empty (first-move detection). */
+  isEmpty(): boolean;
+}
+
+/**
+ * Ruleset carries the per-variant scoring data the validator needs. values is
+ * indexed by alphabet letter index; letterMult/wordMult return the premium
+ * multipliers of a square (1 when none); center is the row-major centre index;
+ * ignoreCrossWords selects the single-word-per-turn rule.
+ */
+export interface Ruleset {
+  cols: number;
+  center: number;
+  rackSize: number;
+  bingo: number;
+  values: readonly number[];
+  letterMult(row: number, col: number): number;
+  wordMult(row: number, col: number): number;
+  ignoreCrossWords: boolean;
+}
+
+/** Dict is the dictionary membership test (see Dawg.indexOf). */
+export interface Dict {
+  indexOf(word: ArrayLike<number>): number;
+}
+
+/** A word formed by a play, with its location, letters (indices) and score. */
+export interface Word {
+  row: number;
+  col: number;
+  dir: Direction;
+  letters: number[];
+  blanks: boolean[];
+  score: number;
+}
+
+/** A scored play: the main word, any cross words, the bingo bonus and the total. */
+export interface Move {
+  dir: Direction;
+  tiles: Placement[];
+  main: Word;
+  cross: Word[];
+  bonus: number;
+  score: number;
+}
+
+/** Reason a play is rejected. Mirrors the error conditions in the Go engine. */
+export type EvalError =
+  | 'empty'
+  | 'not-one-line'
+  | 'off-board'
+  | 'occupied'
+  | 'same-square'
+  | 'gap'
+  | 'too-short'
+  | 'main-not-in-dict'
+  | 'cross-not-in-dict'
+  | 'not-connected';
+
+/** Result of {@link validatePlay}: a scored move plus whether it is legal. */
+export interface ValidateResult {
+  move?: Move;
+  legal: boolean;
+  err?: EvalError;
+}
+
+// coord maps a line coordinate (fixed, axis) to a board (row, col) for dir.
+function coord(dir: Direction, fixed: number, axis: number): [number, number] {
+  return dir === Horizontal ? [fixed, axis] : [axis, fixed];
+}
+
+// fixedAxis is the inverse of coord: it splits (row, col) into (fixed, axis).
+function fixedAxis(dir: Direction, row: number, col: number): [number, number] {
+  return dir === Horizontal ? [row, col] : [col, row];
+}
+
+function perpendicular(d: Direction): Direction {
+  return d === Horizontal ? Vertical : Horizontal;
+}
+
+/**
+ * evaluate computes the words and score for placing tiles on b in direction dir.
+ * It checks geometry only (tiles on one line, on empty squares, contiguous); the
+ * dictionary and connectivity are layered on by {@link validatePlay}. Mirrors
+ * scrabble.EvaluateOpts.
+ */
+export function evaluate(
+  b: Board,
+  rs: Ruleset,
+  dir: Direction,
+  tiles: Placement[],
+): { move?: Move; err?: EvalError } {
+  if (tiles.length === 0) {
+    return { err: 'empty' };
+  }
+
+  const ts = tiles.slice().sort((x, y) => fixedAxis(dir, x.row, x.col)[1] - fixedAxis(dir, y.row, y.col)[1]);
+
+  const fixed = fixedAxis(dir, ts[0].row, ts[0].col)[0];
+  let prevAxis = 0;
+  for (let i = 0; i < ts.length; i++) {
+    const t = ts[i];
+    const [f, a] = fixedAxis(dir, t.row, t.col);
+    if (f !== fixed) return { err: 'not-one-line' };
+    if (!b.inBounds(t.row, t.col)) return { err: 'off-board' };
+    if (b.filled(t.row, t.col)) return { err: 'occupied' };
+    if (i > 0 && a === prevAxis) return { err: 'same-square' };
+    prevAxis = a;
+  }
+
+  const main = buildMainWord(b, rs, dir, fixed, ts);
+  if ('err' in main) return { err: main.err };
+
+  const move: Move = { dir, tiles: ts, main: main.word, cross: [], bonus: 0, score: main.word.score };
+  if (!rs.ignoreCrossWords) {
+    for (const t of ts) {
+      const cw = crossWord(b, rs, dir, t);
+      if (cw) {
+        move.cross.push(cw);
+        move.score += cw.score;
+      }
+    }
+  }
+  if (ts.length === rs.rackSize) {
+    move.bonus = rs.bingo;
+    move.score += rs.bingo;
+  }
+  return { move };
+}
+
+// buildMainWord assembles and scores the word along dir through the sorted
+// placements plus the existing tiles that extend and bridge them. Mirrors
+// scrabble.buildMainWord.
+function buildMainWord(
+  b: Board,
+  rs: Ruleset,
+  dir: Direction,
+  fixed: number,
+  ts: Placement[],
+): { word: Word } | { err: EvalError } {
+  const minA = fixedAxis(dir, ts[0].row, ts[0].col)[1];
+  const maxA = fixedAxis(dir, ts[ts.length - 1].row, ts[ts.length - 1].col)[1];
+
+  let start = minA;
+  for (;;) {
+    const [r, c] = coord(dir, fixed, start - 1);
+    if (!b.filled(r, c)) break;
+    start--;
+  }
+  let end = maxA;
+  for (;;) {
+    const [r, c] = coord(dir, fixed, end + 1);
+    if (!b.filled(r, c)) break;
+    end++;
+  }
+
+  const letters: number[] = [];
+  const blanks: boolean[] = [];
+  let letterSum = 0;
+  let wordMult = 1;
+  let ti = 0;
+  for (let a = start; a <= end; a++) {
+    const [r, c] = coord(dir, fixed, a);
+    if (ti < ts.length) {
+      const ta = fixedAxis(dir, ts[ti].row, ts[ti].col)[1];
+      if (ta === a) {
+        const t = ts[ti];
+        ti++;
+        if (!t.blank) letterSum += rs.values[t.letter] * rs.letterMult(r, c);
+        wordMult *= rs.wordMult(r, c);
+        letters.push(t.letter);
+        blanks.push(t.blank);
+        continue;
+      }
+    }
+    if (b.filled(r, c)) {
+      const cell = b.cellAt(r, c);
+      if (!cell.blank) letterSum += rs.values[cell.letter];
+      letters.push(cell.letter);
+      blanks.push(cell.blank);
+      continue;
+    }
+    return { err: 'gap' };
+  }
+
+  const [wr, wc] = coord(dir, fixed, start);
+  return { word: { row: wr, col: wc, dir, letters, blanks, score: letterSum * wordMult } };
+}
+
+// crossWord builds the perpendicular word formed by a single new tile, or null
+// when the tile has no perpendicular neighbour. Mirrors scrabble.crossWord.
+function crossWord(b: Board, rs: Ruleset, dir: Direction, t: Placement): Word | null {
+  const cdir = perpendicular(dir);
+  const [fixed, axis] = fixedAxis(cdir, t.row, t.col);
+
+  let start = axis;
+  for (;;) {
+    const [r, c] = coord(cdir, fixed, start - 1);
+    if (!b.filled(r, c)) break;
+    start--;
+  }
+  let end = axis;
+  for (;;) {
+    const [r, c] = coord(cdir, fixed, end + 1);
+    if (!b.filled(r, c)) break;
+    end++;
+  }
+  if (start === end) return null;
+
+  const letters: number[] = [];
+  const blanks: boolean[] = [];
+  let letterSum = 0;
+  let wordMult = 1;
+  for (let a = start; a <= end; a++) {
+    const [r, c] = coord(cdir, fixed, a);
+    if (a === axis) {
+      if (!t.blank) letterSum += rs.values[t.letter] * rs.letterMult(r, c);
+      wordMult *= rs.wordMult(r, c);
+      letters.push(t.letter);
+      blanks.push(t.blank);
+    } else {
+      const cell = b.cellAt(r, c);
+      if (!cell.blank) letterSum += rs.values[cell.letter];
+      letters.push(cell.letter);
+      blanks.push(cell.blank);
+    }
+  }
+  const [wr, wc] = coord(cdir, fixed, start);
+  return { row: wr, col: wc, dir: cdir, letters, blanks, score: letterSum * wordMult };
+}
+
+/**
+ * validatePlay scores a play and checks that every word it forms is in the
+ * dictionary and that it connects to the board (or covers the centre on the
+ * first move). legal is true exactly when the play is legal. Mirrors
+ * scrabble.ValidatePlayOpts.
+ */
+export function validatePlay(
+  b: Board,
+  rs: Ruleset,
+  dict: Dict,
+  dir: Direction,
+  tiles: Placement[],
+): ValidateResult {
+  const res = evaluate(b, rs, dir, tiles);
+  if (res.err) return { legal: false, err: res.err };
+  const m = res.move!;
+
+  if (m.main.letters.length < 2) return { move: m, legal: false, err: 'too-short' };
+  if (dict.indexOf(m.main.letters) < 0) return { move: m, legal: false, err: 'main-not-in-dict' };
+  for (const cw of m.cross) {
+    if (dict.indexOf(cw.letters) < 0) return { move: m, legal: false, err: 'cross-not-in-dict' };
+  }
+  if (!connected(b, rs, m)) return { move: m, legal: false, err: 'not-connected' };
+  return { move: m, legal: true };
+}
+
+// connected reports whether the play connects to the position (or covers the
+// centre on the first move). Mirrors (*Solver).connected.
+function connected(b: Board, rs: Ruleset, m: Move): boolean {
+  if (b.isEmpty()) {
+    const cr = Math.floor(rs.center / rs.cols);
+    const cc = rs.center % rs.cols;
+    return wordCovers(m.main, cr, cc);
+  }
+  if (rs.ignoreCrossWords) {
+    return m.main.letters.length > m.tiles.length;
+  }
+  return m.main.letters.length > m.tiles.length || touchesPerpendicular(b, m);
+}
+
+// touchesPerpendicular reports whether any new tile abuts an existing tile
+// perpendicular to the main word. Mirrors scrabble.touchesPerpendicular.
+function touchesPerpendicular(b: Board, m: Move): boolean {
+  const cdir = perpendicular(m.dir);
+  for (const t of m.tiles) {
+    const [fixed, axis] = fixedAxis(cdir, t.row, t.col);
+    let [r, c] = coord(cdir, fixed, axis - 1);
+    if (b.filled(r, c)) return true;
+    [r, c] = coord(cdir, fixed, axis + 1);
+    if (b.filled(r, c)) return true;
+  }
+  return false;
+}
+
+// wordCovers reports whether word w passes through square (r, c). Mirrors
+// scrabble.wordCovers.
+function wordCovers(w: Word, r: number, c: number): boolean {
+  for (let i = 0; i < w.letters.length; i++) {
+    let rr = w.row;
+    let cc = w.col;
+    if (w.dir === Horizontal) cc += i;
+    else rr += i;
+    if (rr === r && cc === c) return true;
+  }
+  return false;
+}

ui/src/lib/i18n/en.ts

@@ -4,6 +4,7 @@
 
 export const en = {
   'app.title': 'Scrabble',
+  'dict.loading': 'Loading…',
   'connection.connecting': 'Connecting…',
 
   'blocked.title': 'Account blocked',

ui/src/lib/i18n/ru.ts

@@ -5,6 +5,7 @@ import type { MessageKey } from './en';
 
 export const ru: Record<MessageKey, string> = {
   'app.title': 'Scrabble',
+  'dict.loading': 'Загрузка…',
   'connection.connecting': 'Подключение…',
 
   'blocked.title': 'Учётная запись заблокирована',

ui/src/lib/mock/client.ts

@@ -161,6 +161,11 @@ export class MockGateway implements GatewayClient {
     // The mock never blocks; the blocked screen is driven directly via the mock-mode __block seam.
     return { blocked: false, permanent: false, until: '', reason: '' };
   }
+  async fetchDict(_variant: Variant, _version: string, _opts?: { signal?: AbortSignal; reload?: boolean }): Promise<ArrayBuffer> {
+    // No local dictionary in mock mode; the caller falls back to the mock evaluate.
+    throw new Error('fetchDict unsupported in mock');
+  }
+
   async gamesList(): Promise<GameList> {
     return {
       games: [...this.games.values()].map((g) => structuredClone(g.view)),
@@ -432,7 +437,7 @@ export class MockGateway implements GatewayClient {
     };
   }
 
-  async evaluate(gameId: string, tiles: PlacedTile[], _variant: Variant): Promise<EvalResult> {
+  async evaluate(gameId: string, tiles: PlacedTile[], _variant: Variant, _signal?: AbortSignal): Promise<EvalResult> {
     const g = this.game(gameId);
     if (tiles.length === 0) return { legal: false, score: 0, words: [], dir: '' };
     let score = tiles.reduce((s, t) => s + valueForLetter(g.view.variant, t.blank ? '?' : t.letter), 0);

ui/src/lib/premiums.ts

@@ -85,5 +85,19 @@ export function centre(variant: Variant): { row: number; col: number } {
   return { row: 7, col: 7 };
 }
 
-// Tile values and the per-variant alphabet now arrive from the server (lib/alphabet.ts);
-// the board geometry above is all this module owns.
+/** RACK_SIZE is the number of tiles drawn to a full rack — 7 for every variant. It sizes
+ *  the all-tiles (bingo) bonus test in the local move preview. */
+export const RACK_SIZE = 7;
+
+/** BINGO is the all-tiles bonus per variant, ported from scrabble-solver/rules/rules.go:
+ *  50 for the Scrabble variants, 15 for Эрудит. The local move preview adds it when a play
+ *  uses the whole rack. The dict conformance test pins these to the engine's rulesets. */
+export const BINGO: Record<Variant, number> = {
+  scrabble_en: 50,
+  scrabble_ru: 50,
+  erudit_ru: 15,
+};
+
+// Tile values and the per-variant alphabet arrive from the server (lib/alphabet.ts); the
+// board geometry, centre, rack size and bingo above are the static per-variant constants
+// this module owns (all ported from scrabble-solver/rules/rules.go).

ui/src/lib/transport.ts

@@ -36,12 +36,13 @@ export function createTransport(baseUrl: string): GatewayClient {
   // exec runs one unary op, auto-retrying transient transport failures with capped backoff (so a
   // dropped connection or a rate-limit recovers seamlessly) and driving the global Connecting
   // indicator. A successful round-trip marks the gateway reachable; a domain result_code is final.
-  async function exec(messageType: string, payload: Uint8Array): Promise<Uint8Array> {
+  async function exec(messageType: string, payload: Uint8Array, signal?: AbortSignal): Promise<Uint8Array> {
     for (let attempt = 0; ; attempt++) {
       let res;
       try {
-        res = await client.execute({ messageType, payload, requestId: '' }, { headers: headers() });
+        res = await client.execute({ messageType, payload, requestId: '' }, { headers: headers(), signal });
       } catch (e) {
+        if (signal?.aborted) throw e; // an intentional cancel (e.g. the tiles moved) — do not retry
         const err = toGatewayError(e);
         if (retryable(err.code, messageType) && attempt < MAX_RETRIES) {
           reportOffline();
@@ -62,6 +63,23 @@ export function createTransport(baseUrl: string): GatewayClient {
       token = t;
     },
 
+    async fetchDict(variant, version, opts) {
+      if (!token) throw new Error('fetchDict: no session');
+      // Low priority so the browser schedules the (large) dictionary behind the game's own
+      // requests — the move eval, state and live events — on a slow link (EDGE). Ignored
+      // where the Priority Hints API is unsupported (iOS WebKit), which is harmless. The
+      // signal aborts a stalled download so it stops holding the channel; reload (the debug
+      // "clear") bypasses the browser HTTP cache to force a fresh copy.
+      const res = await fetch(`${origin}/dict/${encodeURIComponent(variant)}/${encodeURIComponent(version)}`, {
+        headers: { authorization: `Bearer ${token}` },
+        priority: 'low',
+        signal: opts?.signal,
+        cache: opts?.reload ? 'reload' : undefined,
+      } as RequestInit);
+      if (!res.ok) throw new Error(`fetchDict ${variant}/${version}: HTTP ${res.status}`);
+      return res.arrayBuffer();
+    },
+
     async authTelegram(initData) {
       return codec.decodeSession(await exec('auth.telegram', codec.encodeTelegramLogin(initData, browserOffset())));
     },
@@ -119,8 +137,8 @@ export function createTransport(baseUrl: string): GatewayClient {
     async hint(id) {
       return codec.decodeHintResult(await exec('game.hint', codec.encodeGameAction(id)));
     },
-    async evaluate(id, tiles, variant) {
-      return codec.decodeEvalResult(await exec('game.evaluate', codec.encodeEval(id, tiles, variant)));
+    async evaluate(id, tiles, variant, signal) {
+      return codec.decodeEvalResult(await exec('game.evaluate', codec.encodeEval(id, tiles, variant), signal));
     },
     async checkWord(id, word, variant) {
       return codec.decodeWordCheck(await exec('game.check_word', codec.encodeCheckWord(id, word, variant)));