green(reify): implement reify(.enum) — mint a flat enum from TypeInfo

REIFY Phase 0.2 (Phase 0 complete). Lowering.reifyType (lower/nominal.zig)
reads the flat-enum TypeInfo literal off the AST, synthesizes an
ast.EnumDecl, and feeds it through the SAME type_bridge.buildEnumInfo
path source enums use — so the minted type is byte-identical to a
hand-written `enum { value: i64; closed; }` and flows through enum
codegen (layout / construct / match) UNMODIFIED (Contract 2).

Wired at the `E :: reify(...)` const-decl hook in lower/decl.zig
(replacing the Phase-0.0 loud bail). Unsupported argument shapes bail
loudly via reifyBail — never a silent default. The generic.zig inline
reify path now reports it's only supported in a `::` binding (Phase 0).

examples/0614 green: reify a {value: i64, closed} enum, construct
.value(3) and .closed, match both -> "value 3" / "closed". Full suite
green (670 examples, 447 unit).

src/ir/lower.zig

@@ -1703,6 +1703,7 @@ pub const Lowering = struct {
     pub const registerErrorSetDecl = lower_nominal.registerErrorSetDecl;
     pub const registerStructDecl = lower_nominal.registerStructDecl;
     pub const registerEnumDecl = lower_nominal.registerEnumDecl;
+    pub const reifyType = lower_nominal.reifyType;
     pub const registerUnionDecl = lower_nominal.registerUnionDecl;
     pub const qualifyAnonType = lower_nominal.qualifyAnonType;
     pub const nominalIdOf = lower_nominal.nominalIdOf;

src/ir/lower/decl.zig

@@ -651,15 +651,15 @@ pub fn scanDecls(self: *Lowering, decls: []const *const Node) void {
                         .field_access => |fa| fa.field,
                         else => "",
                     };
-                    // `E :: reify(...)` — mint a nominal type from a `TypeInfo`
-                    // and register `E` as an alias to it. The interpreter-side
-                    // construction lands in Phase 0.2; until then bail LOUDLY
-                    // and poison `E` to `.unresolved` (so downstream `E.value`
-                    // gets a clean follow-on, not a silent default type).
+                    // `E :: reify(...)` — mint a NEW nominal type from a
+                    // `TypeInfo` literal and register `E` as an alias to it.
+                    // `reifyType` builds the type (or diagnoses + returns null);
+                    // either way `E` is bound (to the minted type, or poisoned
+                    // to `.unresolved` so downstream `E.value` gets a clean
+                    // follow-on rather than a silent default type).
                     if (std.mem.eql(u8, callee_name, "reify")) {
-                        if (self.diagnostics) |d|
-                            d.addFmt(.err, cd.value.span, "reify is not yet implemented (REIFY Phase 0.2)", .{});
-                        self.putTypeAlias(self.current_source_file, cd.name, .unresolved);
+                        const tid = self.reifyType(cd.name, call_data) orelse TypeId.unresolved;
+                        self.putTypeAlias(self.current_source_file, cd.name, tid);
                         continue;
                     }
                     // A namespaced callee (`ns.Box(..)`) is an explicit qualified

src/ir/lower/generic.zig

@@ -1219,15 +1219,14 @@ pub fn resolveTypeCallWithBindings(self: *Lowering, cl: *const ast.Call) TypeId
         .field_access => |fa| fa.field,
         else => return .unresolved,
     };
-    // Comptime type-construction builtins (REIFY). `reify`/`field_type`
-    // appear in type position (`E :: reify(...)`, `field_type(T, i)` as a
-    // type arg). Until the interpreter-side construction lands (Phase 0.2 /
-    // Phase 2), bail LOUDLY rather than fall through to the misleading
-    // "unknown type 'reify'" diagnostic below — a silent default here would
-    // poison every downstream use of the type.
+    // Comptime type-construction builtins (REIFY). `reify` is minted in a
+    // `::` type-binding position by `decl.zig` (`E :: reify(...)`); reaching it
+    // HERE means an inline type position (`x : reify(...)`, a nested type arg),
+    // which Phase 0 does not support — bail LOUDLY rather than fall through to
+    // the misleading "unknown type 'reify'" diagnostic below.
     if (std.mem.eql(u8, callee_name, "reify")) {
         if (self.diagnostics) |d|
-            d.addFmt(.err, cl.callee.span, "reify is not yet implemented (REIFY Phase 0.2)", .{});
+            d.addFmt(.err, cl.callee.span, "reify is only supported in a `::` type binding (e.g. `E :: reify(...)`) in Phase 0", .{});
         return .unresolved;
     }
     if (std.mem.eql(u8, callee_name, "field_type")) {

src/ir/lower/nominal.zig

@@ -734,6 +734,100 @@ pub fn registerEnumDecl(self: *Lowering, ed: *const ast.EnumDecl) void {
     _ = self.internNamedTypeDecl(decl_key, name_id, info, nominal_id);
 }
 
+/// REIFY Phase 0: mint a NEW nominal enum type from a `TypeInfo` literal passed
+/// to `reify(...)`, registered under `type_name`. The argument shape this phase
+/// supports is exactly the flat-enum literal:
+///
+///   reify(.enum(.{ variants = .[ EnumVariant.{ name = "value", payload = i64 },
+///                                EnumVariant.{ name = "closed", payload = void } ] }))
+///
+/// The variant data is read DIRECTLY off the literal AST (Phase 0 reify takes a
+/// comptime-known literal; the general interp-evaluated path is a later phase),
+/// then handed to the SAME `buildEnumInfo` path source enums use — so the
+/// minted type is byte-identical to an equivalent hand-written `enum { value:
+/// i64; closed; }` and flows through enum codegen (layout / construct / match)
+/// unmodified (Contract 2). Returns the minted `TypeId`, or null after emitting
+/// a diagnostic if the argument is not a shape this phase can build (never a
+/// silent default — REJECTED PATTERNS).
+pub fn reifyType(self: *Lowering, type_name: []const u8, reify_call: *const ast.Call) ?TypeId {
+    const span = reify_call.callee.span;
+    if (reify_call.args.len != 1) return reifyBail(self, span, "reify expects exactly one TypeInfo argument");
+
+    // arg = `.enum(EnumInfo)` — an enum-literal applied as a call.
+    const arg = reify_call.args[0];
+    if (arg.data != .call or arg.data.call.callee.data != .enum_literal)
+        return reifyBail(self, span, "reify Phase 0 supports only `.enum(...)` TypeInfo");
+    const variant_kind = arg.data.call.callee.data.enum_literal.name;
+    if (!std.mem.eql(u8, variant_kind, "enum"))
+        return reifyBail(self, span, "reify Phase 0 supports only the `.enum` TypeInfo variant");
+    if (arg.data.call.args.len != 1)
+        return reifyBail(self, span, "reify `.enum(...)` takes one EnumInfo payload");
+
+    // EnumInfo payload = `.{ variants = .[ ... ] }`.
+    const einfo = arg.data.call.args[0];
+    if (einfo.data != .struct_literal)
+        return reifyBail(self, span, "reify `.enum(...)` payload must be an EnumInfo struct literal");
+    const variants_node = fieldInitValue(&einfo.data.struct_literal, "variants") orelse
+        return reifyBail(self, span, "reify EnumInfo is missing the `variants` field");
+    if (variants_node.data != .array_literal)
+        return reifyBail(self, span, "reify `variants` must be an array literal of EnumVariant");
+
+    // Each element = `EnumVariant.{ name = "...", payload = T }`.
+    var names = std.ArrayList([]const u8).empty;
+    var payloads = std.ArrayList(?*Node).empty;
+    for (variants_node.data.array_literal.elements) |elem| {
+        if (elem.data != .struct_literal)
+            return reifyBail(self, span, "reify variant must be an EnumVariant struct literal");
+        const name_node = fieldInitValue(&elem.data.struct_literal, "name") orelse
+            return reifyBail(self, span, "reify EnumVariant is missing `name`");
+        if (name_node.data != .string_literal)
+            return reifyBail(self, span, "reify EnumVariant `name` must be a string literal");
+        const payload_node = fieldInitValue(&elem.data.struct_literal, "payload") orelse
+            return reifyBail(self, span, "reify EnumVariant is missing `payload`");
+        names.append(self.alloc, name_node.data.string_literal.raw) catch return null;
+        payloads.append(self.alloc, payload_node) catch return null;
+    }
+    if (names.items.len == 0)
+        return reifyBail(self, span, "reify enum has no variants");
+
+    // Hand the synthesized decl to the shared enum body-builder (`self` is the
+    // visibility-aware payload-type resolver, as in registerEnumDecl). A
+    // payload that resolves to `.void` becomes a tagless variant (`closed`),
+    // exactly as a source `enum { … ; closed; }` would.
+    const ed = ast.EnumDecl{
+        .name = type_name,
+        .variant_names = names.items,
+        .variant_types = payloads.items,
+        .is_flags = false,
+        .variant_values = &.{},
+        .backing_type = null,
+        .is_raw = false,
+    };
+    const table = &self.module.types;
+    const info = type_bridge.buildEnumInfo(&ed, table, self);
+    const name_id = table.internString(type_name);
+    const tid = table.findByName(name_id) orelse table.internNominal(info, 0);
+    table.updatePreservingKey(tid, info);
+    return tid;
+}
+
+/// Emit a reify diagnostic and return null — the single loud-failure exit for
+/// `reifyType` (no silent default ever reaches the type table).
+fn reifyBail(self: *Lowering, span: ?ast.Span, comptime msg: []const u8) ?TypeId {
+    if (self.diagnostics) |d| d.addFmt(.err, span, msg, .{});
+    return null;
+}
+
+/// The value node of a named field init in a struct literal, or null if absent.
+fn fieldInitValue(lit: *const ast.StructLiteral, name: []const u8) ?*Node {
+    for (lit.field_inits) |fi| {
+        if (fi.name) |n| {
+            if (std.mem.eql(u8, n, name)) return fi.value;
+        }
+    }
+    return null;
+}
+
 /// Register a top-level UNION decl under a per-decl nominal identity (E6a) —
 /// the union twin of `registerEnumDecl` / `registerStructDecl`.
 pub fn registerUnionDecl(self: *Lowering, ud: *const ast.UnionDecl) void {