feat(scala): m01–m06 port with shared fixtures

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scala/test/Fixtures.test.scala

@@ -2,8 +2,7 @@ package snake
 
 import java.nio.file.{Files, Paths}
 
-/** Loads shared fixtures from ../fixtures/<name>.json.
-  * Typed decoders (point, direction, status, action, state, opt) arrive with the model (Task 11). */
+/** Loads shared fixtures from ../fixtures/<name>.json and decodes them into the course's types. */
 object Fixtures:
   private val dir = Paths.get(sys.props.getOrElse("user.dir", ".")).resolve("..").resolve("fixtures").normalize
 
@@ -16,3 +15,38 @@ object Fixtures:
   /** Decode a nullable JSON value into an Option. */
   def opt[A](v: ujson.Value)(f: ujson.Value => A): Option[A] =
     if v.isNull then None else Some(f(v))
+
+  def point(v: ujson.Value): Point = Point(v("x").num.toInt, v("y").num.toInt)
+
+  def direction(v: ujson.Value): Direction = Direction.valueOf(v.str)
+
+  def status(v: ujson.Value): Status = Status.valueOf(v.str)
+
+  def action(v: ujson.Value): Action = v("tag").str match
+    case "Tick"        => Action.Tick
+    case "Turn"        => Action.Turn(direction(v("dir")))
+    case "TogglePause" => Action.TogglePause
+    case "Restart"     => Action.Restart
+    case "Frame"       => Action.Frame
+    case other         => throw new IllegalArgumentException(s"unknown action tag: $other")
+
+  def gameState(v: ujson.Value): GameState = GameState(
+    width = v("width").num.toInt,
+    height = v("height").num.toInt,
+    snake = v("snake").arr.toList.map(point),
+    dir = direction(v("dir")),
+    nextDir = direction(v("nextDir")),
+    apple = opt(v("apple"))(point),
+    seed = v("seed").num.toLong,
+    score = v("score").num.toInt,
+    status = status(v("status")),
+    frame = v("frame").num.toInt
+  )
+
+  def shape(v: ujson.Value): Shape = v("tag").str match
+    case "Rect" => Shape.Rect(v("x").num.toInt, v("y").num.toInt, v("w").num.toInt, v("h").num.toInt, v("color").str)
+    case "Text" =>
+      Shape.Text(v("x").num.toInt, v("y").num.toInt, v("text").str, v("color").str, v("size").num.toInt, v("align").str)
+    case other => throw new IllegalArgumentException(s"unknown shape tag: $other")
+
+  def list[A](v: ujson.Value)(f: ujson.Value => A): List[A] = v.arr.toList.map(f)