fix(deploy): route /dict through caddy to the gateway (local eval)

The edge caddy @gateway matcher was missing /dict/*, so the client's dictionary
fetch fell to the static landing catch-all: it received a non-dawg blob (200 OK),
which the reader parsed into a bogus finder that reports every word missing — a
valid first move showed as illegal with no network fallback. Add /dict/* to the
gateway route.

Hardening + the cross-test that would have caught it:
- reader: reject a blob whose 32-bit size header != its byte length, so a
  non-dawg page or a truncated download now throws and the loader falls back to
  the network preview instead of silently validating against garbage.
- eval.parity: an adapter conformance suite that drives evaluateLocal through the
  real letter-space path (the server alphabet table, a letter board and letter
  placements) against the engine — the algorithm-level validate.parity did not
  exercise the adapter. validategen now emits the alphabet table for it.
- a CI deploy probe asserts {edge}/dict reaches the gateway (401), not the landing.
- the DebugPanel reports the feature flag, the bad-connection breaker and the
  cached dictionaries with their sizes; its reset also clears the dict cache.

backend/cmd/validategen/main.go

@@ -67,18 +67,28 @@ type fixture struct {
 	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
-	Boards   [][]cell  `json:"boards"`
-	Fixtures []fixture `json:"fixtures"`
+	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() {
@@ -123,7 +133,7 @@ func generate(sp variantSpec, dawgDir, outDir string, games, plies int) error {
 	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),
+		Premiums: premiumCodes(rs), Alphabet: alphabetOf(rs),
 	}
 
 	// Capture under both the standard rule and the single-word rule, building the
@@ -284,6 +294,16 @@ func toWord(w scrabble.Word) *word {
 	}
 }
 
+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 {