diff --git a/spec/tests/test-cross-lang-types.sx b/spec/tests/test-cross-lang-types.sx
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+;; Step 7: Cross-language type primitives
+;; Threading variants, destructuring, protocols/traits, satisfies?
+
+;; ── Thread-last (->>) ─────────────────────────────────────────────
+
+(defsuite
+  "thread-last"
+  (deftest "basic thread-last" (assert= (->> 1 (+ 10)) 11))
+  (deftest
+    "thread-last multi-step"
+    (assert=
+      (->> (list 1 2 3 4) (filter odd?) (map (fn (x) (* x 10))))
+      (list 10 30)))
+  (deftest
+    "thread-last into collection ops"
+    (assert=
+      (->>
+        (list 1 2 3)
+        (map (fn (x) (* x 2)))
+        (filter even?)
+        (join ", "))
+      "2, 4, 6"))
+  (deftest "thread-last single form" (assert= (->> 5 (+ 1)) 6))
+  (deftest
+    "thread-last bare function"
+    (assert= (->> (list 3 1 2) reverse) (list 2 1 3))))
+
+;; ── Thread-as (as->) ──────────────────────────────────────────────
+
+(defsuite
+  "thread-as"
+  (deftest "basic as->" (assert= (as-> 10 x (+ x 1) (* x 2)) 22))
+  (deftest
+    "as-> mid-position"
+    (assert= (as-> (list 1 2 3) v (len v) (+ v 10)) 13))
+  (deftest
+    "as-> with string ops"
+    (assert= (as-> "hello" s (str s " world") (upper s)) "HELLO WORLD"))
+  (deftest "as-> single step" (assert= (as-> 5 x (* x x)) 25)))
+
+;; ── define-protocol / implement ───────────────────────────────────
+
+(define-protocol Greetable (greet self))
+
+(define-protocol Measurable (measure self) (unit self))
+
+(define-record-type
+  <person>
+  (make-person name age)
+  person?
+  (name person-name)
+  (age person-age))
+
+(define-record-type
+  <box>
+  (make-box width height)
+  box?
+  (width box-width)
+  (height box-height))
+
+(implement
+  Greetable
+  <person>
+  (greet self (str "Hello, " (person-name self) "!")))
+
+(implement
+  Measurable
+  <box>
+  (measure self (* (box-width self) (box-height self)))
+  (unit self "sq-units"))
+
+(defsuite
+  "protocol-basic"
+  (deftest
+    "protocol method dispatches on type"
+    (let
+      ((p (make-person "Alice" 30)))
+      (assert= (greet p) "Hello, Alice!")))
+  (deftest
+    "protocol with multiple methods"
+    (let
+      ((b (make-box 3 4)))
+      (assert= (measure b) 12)
+      (assert= (unit b) "sq-units")))
+  (deftest
+    "unimplemented protocol raises error"
+    (let
+      ((b (make-box 5 5)) (raised false))
+      (guard (e (true (set! raised true))) (greet b))
+      (assert raised "should raise for unimplemented"))))
+
+(defsuite
+  "protocol-satisfies"
+  (deftest
+    "satisfies? true for implemented"
+    (let ((p (make-person "Bob" 25))) (assert (satisfies? "Greetable" p))))
+  (deftest
+    "satisfies? false for not implemented"
+    (let
+      ((p (make-person "Bob" 25)))
+      (assert (not (satisfies? "Measurable" p)))))
+  (deftest
+    "satisfies? true for second protocol"
+    (let ((b (make-box 1 1))) (assert (satisfies? "Measurable" b))))
+  (deftest
+    "satisfies? false for unknown protocol"
+    (let
+      ((p (make-person "X" 1)))
+      (assert (not (satisfies? "Unknown" p))))))
+
+;; ── Multiple implementations ──────────────────────────────────────
+
+(implement
+  Greetable
+  <box>
+  (greet self (str "Box " (box-width self) "x" (box-height self))))
+
+(defsuite
+  "protocol-multi-impl"
+  (deftest
+    "same protocol different types"
+    (let
+      ((p (make-person "Eve" 20)) (b (make-box 2 3)))
+      (assert= (greet p) "Hello, Eve!")
+      (assert= (greet b) "Box 2x3")))
+  (deftest
+    "satisfies? after adding impl"
+    (let ((b (make-box 1 1))) (assert (satisfies? "Greetable" b)))))