docs+rename: erase the reify name everywhere — stream is METATYPE

The compiler concept is declare/define (comptime type construction); the
old "reify" framing is gone from the entire repo.

- Rename: PLAN-REIFY → PLAN-METATYPE, CHECKPOINT-REIFY → CHECKPOINT-METATYPE,
  PLAN-POST-REIFY → PLAN-POST-METATYPE (both rewritten around declare/define);
  examples 0614/0615/0617 → comptime-metatype-* (+ their expected/ triplets),
  headers rewritten.
- Scrub reify from design/execution-evolution-roadmap.md (§7 step 3 contracts,
  §8.1, §9 decisions, §10 gates) → declare/define / comptime type construction.
- core.sx prelude pointer + parser.test.zig surface lock updated to the
  declare/define builtins (define(handle, info) -> Type; EnumInfo.name).

No behavior change; renamed examples match their renamed snapshots. Full
suite green (673), all unit tests pass. Zero `reify` tokens remain in
src/docs/sx/examples.

examples/0614-comptime-metatype-enum.sx

@@ -1,7 +1,8 @@
-// REIFY Phase 0: mint a NEW nominal enum from a `TypeInfo` value at comptime,
-// then construct one of its variants and match on it — exercising that a
-// reify'd enum (with NO backing AST decl) flows through enum codegen unmodified
-// (layout / construct / match), Contract 2.
+// Comptime type construction: mint a NEW nominal enum from a `TypeInfo` value
+// via the `define(declare(), info)` primitives, then construct one of its
+// variants and match on it — exercising that a programmatically-built enum
+// (with NO backing AST decl) flows through enum codegen unmodified (layout /
+// construct / match), byte-identical to a hand-written enum.
 //
 // The enum has two variants: `value` carrying an i64 payload, and `closed` with
 // no payload (`payload = void`).

examples/0615-comptime-metatype-typefn-identity.sx

@@ -1,10 +1,10 @@
-// REIFY Phase 1: a type-fn that RETURNS `reify(...)` must memoize by the
-// instantiation's mangled name, so `Box(i64)` resolved at two INDEPENDENT sites
-// (here: a return type and a parameter type) is ONE `TypeId`. A value built at
-// one site is therefore assignable / matchable at the other — nominal identity
-// (Contract 1). If the reify result were not registered under the mangled
-// instantiation name, the two sites would mint distinct types and
-// `consume(build())` would be a type error.
+// Comptime type construction — identity: a type-fn that builds a type with
+// `define(declare(), ...)` must memoize by the instantiation's mangled name, so
+// `Box(i64)` resolved at two INDEPENDENT sites (here: a return type and a
+// parameter type) is ONE `TypeId`. A value built at one site is therefore
+// assignable / matchable at the other — nominal identity. If the minted result
+// were not registered under the mangled instantiation name, the two sites would
+// mint distinct types and `consume(build())` would be a type error.
 #import "modules/std.sx";
 #import "modules/std/meta.sx";
 

examples/0616-comptime-field-type.sx

@@ -1,5 +1,6 @@
-// REIFY Phase 2: `field_type($T, i) -> Type` — the type-only field projection
-// the value-level reflection (`field_value` / `type_of`) couldn't express.
+// Comptime reflection: `field_type($T, i) -> Type` — the type-only field
+// projection the value-level reflection (`field_value` / `type_of`) couldn't
+// express.
 // Reflect a struct's fields by name (`field_name`) AND by type (`field_type`),
 // and a tagged-union's variant payloads. It folds at lower time, so it composes
 // inside `type_eq` / `type_name` / any type-arg slot.

examples/0617-comptime-metatype-channel-results.sx

@@ -1,9 +1,10 @@
-// REIFY Phase 3: RecvResult($T) / TryResult($T) — the channel result types,
-// built ENTIRELY in sx library code as type-fns over `reify` (no new compiler
-// machinery beyond Phases 0–1). A blocking recv yields a value or a `closed`
-// marker; a non-blocking try-recv adds `empty` — three states a bool can't
-// express. This locks that they construct and match like any enum, and that
-// `RecvResult(i64)` is one nominal type across sites (the type-fn identity path).
+// Comptime type construction — channel result types: RecvResult($T) /
+// TryResult($T), built ENTIRELY in sx library code as type-fns over the
+// `define(declare(), ...)` primitives (no compiler machinery). A blocking recv
+// yields a value or a `closed` marker; a non-blocking try-recv adds `empty` —
+// three states a bool can't express. This locks that they construct and match
+// like any enum, and that `RecvResult(i64)` is one nominal type across sites
+// (the type-fn identity path).
 #import "modules/std.sx";
 #import "modules/std/meta.sx";