cl: block + return-from — 13 new tests (140 eval, 312 total green)

Sentinel propagation in cl-eval-body; cl-eval-block catches matching
sentinels; BLOCK/RETURN-FROM/RETURN dispatch added to cl-eval-list.
Parser: CL strings now {:cl-type "string"} dicts for proper CL semantics.

lib/common-lisp/tests/eval.sx

@@ -283,3 +283,45 @@
 (cl-test "mapcar: basic"
   (ev "(mapcar (lambda (x) (* x 2)) '(1 2 3))")
   (list 2 4 6))
+
+;; ── BLOCK / RETURN-FROM / RETURN ─────────────────────────────────
+
+(cl-test "block: last form value"
+  (ev "(block done 1 2 3)")
+  3)
+(cl-test "block: empty body"
+  (ev "(block done)")
+  nil)
+(cl-test "block: single form"
+  (ev "(block foo 42)")
+  42)
+(cl-test "block: return-from"
+  (ev "(block done 1 (return-from done 99) 2)")
+  99)
+(cl-test "block: return-from nil block"
+  (ev "(block nil 1 (return-from nil 42) 3)")
+  42)
+(cl-test "block: return-from no value"
+  (ev "(block done (return-from done))")
+  nil)
+(cl-test "block: nested inner return stays inner"
+  (ev "(block outer (block inner (return-from inner 1) 2) 3)")
+  3)
+(cl-test "block: nested outer return"
+  (ev "(block outer (block inner 1 2) (return-from outer 99) 3)")
+  99)
+(cl-test "return: shorthand for nil block"
+  (ev "(block nil (return 77))")
+  77)
+(cl-test "return: no value"
+  (ev "(block nil 1 (return) 2)")
+  nil)
+(cl-test "block: return-from inside let"
+  (ev "(block done (let ((x 5)) (when (> x 3) (return-from done x))) 0)")
+  5)
+(cl-test "block: return-from inside progn"
+  (ev "(block done (progn (return-from done 7) 99))")
+  7)
+(cl-test "block: return-from through function"
+  (ev "(block done (flet ((f () (return-from done 42))) (f)) nil)")
+  42)