Separate core spec from web framework

Three-layer architecture:
  spec/  — Core language (19 files): evaluator, parser, primitives,
           CEK machine, types, continuations. Host-independent.
  web/   — Web framework (20 files): signals, adapters, engine,
           orchestration, boot, router, CSSX. Built on core spec.
  sx/    — Application (sx-docs website). Built on web framework.

Split boundary.sx into boundary-core.sx (type-of, make-env, identical?)
and boundary-web.sx (IO primitives, signals, spreads, page helpers).

Bootstrappers search spec/ → web/ → shared/sx/ref/ for .sx files.
Original files remain in shared/sx/ref/ as fallback during transition.
All 63 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

spec/boundary-core.sx

@@ -0,0 +1,49 @@
+;; ==========================================================================
+;; boundary.sx — SX language boundary contract
+;;
+;; Declares the core I/O primitives that any SX host must provide.
+;; This is the LANGUAGE contract — not deployment-specific.
+;;
+;; Pure primitives (Tier 1) are declared in primitives.sx.
+;; Deployment-specific I/O lives in boundary-app.sx.
+;; Per-service page helpers live in {service}/sx/boundary.sx.
+;;
+;; Format:
+;;   (define-io-primitive "name"
+;;     :params (param1 param2 &key ...)
+;;     :returns "type"
+;;     :effects [io]
+;;     :async true
+;;     :doc "description"
+;;     :context :request)
+;;
+;; ==========================================================================
+
+
+;; --------------------------------------------------------------------------
+;; Tier 1: Pure primitives — declared in primitives.sx
+;; --------------------------------------------------------------------------
+
+(declare-tier :pure :source "primitives.sx")
+
+
+;; --------------------------------------------------------------------------
+;; Core platform primitives — type inspection + environment
+;; --------------------------------------------------------------------------
+;;
+;; These are provided by every host. Not IO, not web-specific.
+
+(declare-core-primitive "type-of"
+  :params (value)
+  :returns "string"
+  :doc "Return the type name of a value.")
+
+(declare-core-primitive "make-env"
+  :params ()
+  :returns "dict"
+  :doc "Create a base environment with all primitives.")
+
+(declare-core-primitive "identical?"
+  :params (a b)
+  :returns "boolean"
+  :doc "Reference equality check.")