engine: the chosen candidate is what the client shows

The preedit sent back to the owner was always impre(), the reading, so
かく stayed underlined in the application while the popup showed 書く and
Enter inserted 書く.  Nothing was hidden -- the popup had it -- but the
text did not stand where it was going to land, and mozc, fcitx5 and kime
all put the candidate inline.

Only the reply changes.  impre() still answers the reading everywhere it
is the reading that is wanted: commitim, the okurigana mark, the seed
Ctrl+H takes, and snapshot, so a popup that draws the preedit itself
keeps the reading above the list where it says something the highlighted
row does not.  Consulting im.sel here is safe where consulting it inside
impre() would not be: transstr memsets a local Im, whose sel is 0 and not
-1, and this reply only ever reads the engine's own.

Nothing in the suite pinned the old answer, so the test is new.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -33,16 +33,17 @@ Japanese composes a whole reading and then offers its Kanji with none
 chosen. `Space` and `Tab` step through the candidates and wrap (`Shift`
 reverses), the reading in Katakana last, so a word the dictionary lacks
 converts with one `Space`; `Up`/`Down` and `PageUp`/`PageDown` move without
-wrapping. `Enter` commits the chosen candidate, or the reading, as `0` and
-typing on always do. Once a candidate is chosen `1`-`9` take that row of
-the page shown; before that the digits type. `Backspace` deletes the last
-kana shown, and romaji that made no kana stays as typed until it is mended;
-`Esc` cancels the reading, and on a chosen candidate both go back to it.
-The dictionary keys verbs and adjectives by stem and okurigana, so `kaku`
-offers かく's readings and then 書く and its kin — typing the okurigana
-with `Shift`, as SKK does, `kaKu`, asks for that split first. Katakana
-mode does not convert, so there `Space` and `Tab` commit the reading and
-go on to the application.
+wrapping. A chosen candidate takes the reading's place in the preedit, so
+it stands where it will land, and `Enter` commits it, or the reading, as
+`0` and typing on always do. Once a candidate is chosen `1`-`9` take that
+row of the page shown; before that the digits type. `Backspace` deletes
+the last kana shown, and romaji that made no kana stays as typed until it
+is mended; `Esc` cancels the reading, and on a chosen candidate both go
+back to it. The dictionary keys verbs and adjectives by stem and
+okurigana, so `kaku` offers かく's readings and then 書く and its kin —
+typing the okurigana with `Shift`, as SKK does, `kaKu`, asks for that
+split first. Katakana mode does not convert, so there `Space` and `Tab`
+commit the reading and go on to the application.
 
 Korean composes one syllable at a time. `Enter`, `Tab`, `Esc` and any key
 that is not a jamo commit the syllable and go on to the application, so

strans.c

@@ -1097,6 +1097,8 @@ imhandlekey(Keyreq *kr)
 	if(kr->owner == activeowner){
 		if(search.lang)
 			searchpre(&res.preedit);
+		else if(im.sel >= 0)
+			res.preedit = im.kouho[im.sel];	/* what Enter would commit */
 		else
 			impre(&im, &res.preedit);
 	}

tests/engine_test.c

@@ -411,6 +411,7 @@ engine_commit_contract(struct ct *t)
 		{ 'd', "ㅇ", "ㅇㅇㅇ" },
 		{ 'k', "ㅏ", "ㅏㅏㅏ" },
 	};
+	Drawcmd dc;
 	Keyres res;
 	Str all, com;
 	char owner;
@@ -495,6 +496,26 @@ engine_commit_contract(struct ct *t)
 	CT_CHECK(t, !keystroke(0xf008, 0, &com));
 	checkstr(t, "non-ASCII key commit", "か", &com);
 	CT_EQ_INT(t, 0, im.pre.n);
+
+	/* A chosen candidate is what the client shows and what Enter
+	 * commits; the popup keeps the reading above the list. */
+	init();
+	im.l = getlang(LangJP);
+	draindraw(nil);
+	ownerrequestcap(&owner, 1, Keypress, 'k', 0);
+	res = ownerrequestcap(&owner, 1, Keypress, 'a', 0);
+	checkstr(t, "the reading before a candidate", "か", &res.preedit);
+	im.kouho[0] = mkstr("蚊");
+	im.nkouho = 1;
+	res = ownerrequestcap(&owner, 1, Keypress, Kdown, 0);
+	checkstr(t, "the candidate the client shows", "蚊", &res.preedit);
+	clientpre = 0;
+	redraw();
+	if(CT_CHECK(t, draindraw(&dc) > 0))
+		checkstr(t, "the popup keeps the reading", "か", &dc.pre);
+	res = ownerrequestcap(&owner, 1, Keypress, Kret, 0);
+	checkstr(t, "Enter commits what was shown", "蚊", &res.commit);
+	CT_EQ_INT(t, 0, res.preedit.n);
 }
 
 void