engine: じ is keyed j, the letter SKK types it with

okuriletter() puts じ in the z row, so dictqokuri can never build a key
ending in j.  map/kanji.dict has 17 of them, and 8 have no z twin at all:

	before                     after
	shinjiru  死んじる           信じる 死んじる
	tojiru    (nothing)        綴じる 閉じる
	tsuujiru  (nothing)        通じる
	shoujiru  (nothing)        生じる
	toujiru   問うじる           投じる 問うじる
	koujiru   乞うじる 請うじる    高じる 乞うじる 請うじる
	gozonji   御存知             御存知 御存じ
	majiru    混じる 先じる       交じる 混じる

信じる, 閉じる, 通じる, 生じる, 投じる, 交じる: the dictionary holds every
one and the engine could reach none.  What it offered instead was the
next split down -- しんじる falls back to しn, so 死んじる is what the
popup shows for 信じる, and it is the only candidate.

The letter is not ours to choose; it is the one the SKK dictionary was
keyed by, which is the one the user typed.  Real SKK carries both spellings
where both are typed, and here that is 9 of the 17 -- えんj/えんz, かんj/かんz
and their kin, identical values on both.  Those 8 z rows go unreachable and
lose nothing, because their j twin says the same word.  ま is the one pair
that differs, まj=交 混 against まz=混 先, and both stay reachable: じ takes
the j road and ぜ/ず keep the z one.

	mazeru    混ぜる 先ぜる      unchanged
	kanarazu  必ず ...           unchanged
	mizu      水 見ず            unchanged
	dekizu    出来ず             unchanged

The z row keeps ざずぜぞ, so nothing that is not じ moves.

What this does not cover, deliberately: ち.  kanji.dict has 7 keys ending
in c, from users who typed "chi", and okuriletter puts ち in the t row.
Giving c its own row would have to take ち out of t, and t is where the
larger entry lives -- おt is 落 折 負 追 against おc's 落 alone -- so the c
rows stay unreachable and lose nothing.  づ needed no such choice: it is
in the d row, もとd is 基, and もとz is its duplicate.

strans.c

@@ -266,7 +266,8 @@ okuriletter(Rune r)
 {
 	static char *rows[] = {
 		"aあ", "iい", "uう", "eえ", "oお",
-		"kかきくけこ", "gがぎぐげご", "sさしすせそ", "zざじずぜぞ",
+		"kかきくけこ", "gがぎぐげご", "sさしすせそ", "zざずぜぞ",
+		"jじ",
 		"tたちつてとっ", "dだぢづでど", "nなにぬねのん", "hはひふへほ",
 		"bばびぶべぼ", "pぱぴぷぺぽ", "mまみむめも", "yやゆよ",
 		"rらりるれろ", "wわ",

tests/engine_test.c

@@ -1282,6 +1282,19 @@ engine_japanese_candidates(struct ct *t)
 		checkstr(t, "sokuon written in kana", "行った", &im.kouho[1]);
 	}
 	CT_CHECK(t, keystroke(Kesc, 0, &com));
+	/* じ is keyed j, as SKK types it; ざずぜぞ keep z. */
+	setdict(jp->dict, "しんj", "信");
+	setdict(jp->dict, "まz", "混");
+	if(!typekeys(t, "shinjiru", &com))
+		goto cleanup;
+	if(CT_EQ_INT(t, 1, im.nkouho))
+		checkstr(t, "じ okurigana", "信じる", &im.kouho[0]);
+	CT_CHECK(t, keystroke(Kesc, 0, &com));
+	if(!typekeys(t, "mazeru", &com))
+		goto cleanup;
+	if(CT_EQ_INT(t, 1, im.nkouho))
+		checkstr(t, "ぜ okurigana", "混ぜる", &im.kouho[0]);
+	CT_CHECK(t, keystroke(Kesc, 0, &com));
 	/* A romaji typo stays in the reading for Backspace to mend. */
 	if(!typekeys(t, "kanjr", &com))
 		goto cleanup;