chore: scaffold tracks and tooling

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

fsharp/tests/M00Sanity.fs

@@ -0,0 +1,23 @@
+module Snake.Tests.M00Sanity
+
+open System.Text.Json
+open Expecto
+open Snake.Tests
+
+[<Tests>]
+let tests =
+    testList "M00 sanity" [
+        test "arithmetic" { Expect.equal (1 + 1) 2 "1 + 1" }
+
+        test "fixture loads and cases hold" {
+            Expect.equal ((Fixtures.load "m00-sanity").GetProperty("function").GetString()) "sanity" "function"
+            for c in Fixtures.cases "m00-sanity" do
+                let a = c.GetProperty("args").EnumerateArray() |> Seq.map (fun e -> e.GetInt32()) |> List.ofSeq
+                Expect.equal (List.sum a) (c.GetProperty("expected").GetInt32()) (c.GetProperty("name").GetString())
+        }
+
+        test "opt decodes null" {
+            use d = JsonDocument.Parse("null")
+            Expect.isNone (Fixtures.opt (fun e -> e.GetInt32()) d.RootElement) "null"
+        }
+    ]