test(metatype): lock type_info round-trip example (currently bails)

type_info($T) is still unimplemented, so the round-trip
define(declare("ShapeCopy"), type_info(Shape)) bails with
"type_info is not yet implemented" plus the downstream
enum-inference cascade. Snapshot pins that current behavior;
the next commit implements type_info and turns this green.

examples/0619-comptime-metatype-type-info.sx

@@ -0,0 +1,34 @@
+// Comptime reflection — `type_info($T)`: reflect a SOURCE enum INTO a `TypeInfo`
+// value, then feed that value straight back to `define` to mint a byte-identical
+// copy. This is the inverse of `define`'s decode: `type_info` reads a type's
+// variants (name + payload type) out of the type table and constructs the same
+// `.enum(EnumInfo{ variants })` value the `define` examples write by hand.
+//
+// Round-trip: `ShapeCopy` is reconstructed purely from `type_info(Shape)` — no
+// literal variant list — and constructs/matches like the original.
+#import "modules/std.sx";
+#import "modules/std/meta.sx";
+
+Shape :: enum {
+    circle: f64;
+    rect: i64;
+    empty;
+}
+
+// Reflect Shape → TypeInfo, then reconstruct an identical nominal enum.
+ShapeCopy :: define(declare("ShapeCopy"), type_info(Shape));
+
+describe :: (s: ShapeCopy) {
+    if s == {
+        case .circle: (r) { print("circle r={}\n", r); }
+        case .rect:   (n) { print("rect n={}\n", n); }
+        case .empty:       { print("empty\n"); }
+    }
+}
+
+main :: () -> i32 {
+    describe(.circle(2.5));
+    describe(.rect(7));
+    describe(.empty);
+    return 0;
+}

examples/expected/0619-comptime-metatype-type-info.exit

@@ -0,0 +1 @@
+1

examples/expected/0619-comptime-metatype-type-info.stderr

@@ -0,0 +1,17 @@
+error: type_info is not yet implemented
+  --> examples/0619-comptime-metatype-type-info.sx:19:43
+   |
+19 | ShapeCopy :: define(declare("ShapeCopy"), type_info(Shape));
+   |                                           ^^^^^^^^^
+
+error: cannot infer enum type for '.circle' — use an explicit type or assign to a typed variable
+  --> examples/0619-comptime-metatype-type-info.sx:30:14
+   |
+30 |     describe(.circle(2.5));
+   |              ^^^^^^^
+
+error: cannot infer enum type for '.rect' — use an explicit type or assign to a typed variable
+  --> examples/0619-comptime-metatype-type-info.sx:31:14
+   |
+31 |     describe(.rect(7));
+   |              ^^^^^

examples/expected/0619-comptime-metatype-type-info.stdout

@@ -0,0 +1 @@
+