Step 10c: Vector type + unified reactive model test spec (34 tests)

- Vector of value array added to sx_types.ml (prior commit)
- Vector primitives in sx_primitives.ml (make-vector, vector-ref,
  vector-set!, vector-length, vector->list, list->vector)
- R7RS vector tests
- test-unified-reactive.sx: 34 tests specifying the unified reactive
  model (provide/context/peek/bind replacing signal/deref split).
  All 34 currently fail — implementation next.
- WASM binary rebuilt

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

spec/tests/test-r7rs.sx

@@ -577,3 +577,85 @@
       (with-capabilities
         (list "pure")
         (fn () (assert (capability-restricted?)))))))
+
+(defsuite
+  "unified-reactive"
+  (deftest
+    "provide-reactive! stores signal in scope"
+    (begin
+      (provide-reactive! "theme" "dark")
+      (let
+        ((result (context "theme")))
+        (provide-pop-reactive! "theme")
+        (assert= "dark" result))))
+  (deftest
+    "provide-set! mutates reactive value"
+    (begin
+      (provide-reactive! "count" 0)
+      (assert= 0 (context "count"))
+      (provide-set! "count" 42)
+      (let
+        ((result (context "count")))
+        (provide-pop-reactive! "count")
+        (assert= 42 result))))
+  (deftest
+    "peek reads without tracking"
+    (begin
+      (provide-reactive! "x" 10)
+      (tracking-start!)
+      (let
+        ((v (peek "x")))
+        (let
+          ((deps (tracking-stop!)))
+          (provide-pop-reactive! "x")
+          (assert= 10 v)
+          (assert= 0 (len deps))))))
+  (deftest
+    "context registers in tracking context"
+    (begin
+      (provide-reactive! "y" 20)
+      (tracking-start!)
+      (let
+        ((v (context "y")))
+        (let
+          ((deps (tracking-stop!)))
+          (provide-pop-reactive! "y")
+          (assert= 20 v)
+          (assert= 1 (len deps))))))
+  (deftest
+    "context without tracking does not register"
+    (begin
+      (provide-reactive! "z" 30)
+      (assert (not (tracking-active?)))
+      (let ((v (context "z"))) (provide-pop-reactive! "z") (assert= 30 v))))
+  (deftest
+    "nested reactive provides"
+    (begin
+      (provide-reactive! "n" "outer")
+      (provide-reactive! "n" "inner")
+      (assert= "inner" (context "n"))
+      (provide-pop-reactive! "n")
+      (assert= "outer" (context "n"))
+      (provide-pop-reactive! "n")))
+  (deftest
+    "peek falls back to non-reactive scope"
+    (begin
+      (scope-push! "plain" 42)
+      (let ((v (peek "plain"))) (scope-pop! "plain") (assert= 42 v))))
+  (deftest
+    "tracking-active? predicate"
+    (begin
+      (assert (not (tracking-active?)))
+      (tracking-start!)
+      (assert (tracking-active?))
+      (tracking-stop!)
+      (assert (not (tracking-active?)))))
+  (deftest
+    "provide-set! updates visible value"
+    (begin
+      (provide-reactive! "mut" "old")
+      (provide-set! "mut" "new")
+      (let
+        ((v (context "mut")))
+        (provide-pop-reactive! "mut")
+        (assert= "new" v)))))