docs(metatype): type_info($T) enum reflection done; update plan/checkpoint

current/PLAN-METATYPE.md

@@ -10,7 +10,8 @@ Comptime type metaprogramming with the smallest possible compiler surface:
 - **`define(handle, info) -> Type`** — fill a declared handle's body from a
   `TypeInfo` *value*, and return the handle (so the one-shot form chains).
 - **`type_info($T) -> TypeInfo`** — reflect a type INTO data (the inverse of
-  `define`'s decode). *Pending.*
+  `define`'s decode). *Done for enums* (`interp.zig:reflectTypeInfo`,
+  `examples/0619`); struct/tuple widening pending.
 - **`field_type($T, i) -> Type`** — the i-th field / variant-payload / element
   type of `$T`. *Done.*
 
@@ -109,10 +110,12 @@ while red. Examples: `06xx` (comptime), `11xx` (diagnostics).
 - [ ] **`make_enum(variants: []EnumVariant)`** sx helper over a COMPUTED
       (non-literal) variant list — exercises the interpreter decoding a value-arg
       slice in `define`.
-- [ ] **`type_info($T) -> TypeInfo`** — reflect a type INTO a value (inverse of
-      `define`'s decode): widen `TypeInfo` past `` `enum `` (struct/tuple) AND
-      construct a `[]EnumVariant`-style value in the interpreter. Bails loudly today
-      in `call.zig:tryLowerReflectionCall`. Round-trips through `define` once it lands.
+- [x] **`type_info($T) -> TypeInfo`** (enum-only) — reflect an `enum`/`tagged_union`
+      INTO a value (inverse of `define`'s decode): `interp.zig:reflectTypeInfo`
+      constructs the `.enum(EnumInfo{ variants })` Value `defineEnum` decodes, so
+      `define(declare(n), type_info(T))` round-trips. `examples/0619`. Non-enum args
+      rejected loudly at lower time. **Still pending:** widen `TypeInfo` past
+      `` `enum `` (struct/tuple variants) + the matching `define` decode arms.
 - [~] **Validation + loud diagnostics** — by-VALUE self-reference DONE
       (`checkInfiniteSize` Pass 1g: loud "infinitely sized" diagnostic + cycle
       break, covers source + comptime types; `examples/1178`, issue 0139 resolved).