fix(go): repair migration wire contracts and runtime lifecycle; document incomplete port

pkg/protocol/uxreader.go

@@ -103,18 +103,22 @@ func (r *UxReader) F64() (float64, error) {
 }
 
 func (r *UxReader) ReadVarInt() (int, error) {
-	shift := 0
-	result := 0
-	for r.pos < len(r.data) {
-		b := r.data[r.pos]
-		r.pos++
-		result |= int(b&0x7F) << shift
-		if (b & 0x80) == 0 {
-			return result, nil
+	// UX lengths/counts are nonnegative Int32 values, at most five bytes.
+	var result uint32
+	for shift := uint(0); shift < 35; shift += 7 {
+		b, err := r.U8()
+		if err != nil {
+			return 0, errors.New("unterminated varint")
+		}
+		if shift == 28 && b > 7 {
+			return 0, errors.New("varint exceeds Int32")
+		}
+		result |= uint32(b&0x7f) << shift
+		if b&0x80 == 0 {
+			return int(result), nil
 		}
-		shift += 7
 	}
-	return result, errors.New("unterminated varint")
+	return 0, errors.New("varint exceeds Int32")
 }
 
 func (r *UxReader) Int7() (int, error) {