smalltalk: Object>>becomeForward: + 6 tests

lib/smalltalk/eval.sx

@@ -565,6 +565,24 @@
             (cond
               ((not (st-class-ref? arg)) false)
               (else (= target-cls (get arg :name))))))
+        ;; Object>>becomeForward: aReceiver — one-way become. The receiver's
+        ;; class and ivars are mutated in place to match the target. Every
+        ;; existing reference to the receiver dict sees the new identity.
+        ;; Note: receiver and target remain distinct dicts (not == in the
+        ;; SX-identity sense), but receiver behaves as though it were the
+        ;; target — which is the practical Pharo guarantee.
+        ((= selector "becomeForward:")
+          (let ((other (nth args 0)))
+            (cond
+              ((not (st-instance? receiver))
+                (error "becomeForward: only supported on user instances"))
+              ((not (st-instance? other))
+                (error "becomeForward: target must be a user instance"))
+              (else
+                (begin
+                  (dict-set! receiver :class (get other :class))
+                  (dict-set! receiver :ivars (get other :ivars))
+                  receiver)))))
         ((or (= cls "SmallInteger") (= cls "Float"))
           (st-num-send receiver selector args))
         ((or (= cls "String") (= cls "Symbol"))