fix(frontends): preserve preedit lifecycle

tests/engine_test.c

@@ -396,7 +396,25 @@ engine_active_owner_caret(struct ct *t)
 void
 engine_commit_contract(struct ct *t)
 {
-	Str com;
+	Keyres res;
+	Str all, com;
+	char owner;
+	int i;
+
+	init();
+	im.l = getlang(LangKO);
+	sclear(&all);
+	for(i = 0; i < 3; i++){
+		res = ownerrequestcap(&owner, Cclientpreedit,
+			Keypress, 'z', 0);
+		CT_CHECK(t, res.eaten);
+		checkstr(t, "repeated consonant commit",
+			i == 0 ? "" : "ㅋ", &res.commit);
+		checkstr(t, "repeated consonant preedit", "ㅋ", &res.preedit);
+		sappend(&all, &res.commit);
+	}
+	sappend(&all, &res.preedit);
+	checkstr(t, "repeated consonant total", "ㅋㅋㅋ", &all);
 
 	init();
 	im.l = getlang(LangJP);