libhangul, and so fcitx5-hangul, joins two lone consonants into the
compound jong they make (rt → ㄳ, split again by a vowel: rtk → ㄱ사),
and by default reorders a vowel typed before its consonant (kr → 가);
strans committed the first jamo and started over. Backspace on a lone
ㄳ leaves ㄱ, as on a syllable.
The three jamo index tables and their -1 macros were the cho, jung, and
jong arrays inverted by hand, bounded by a Jrange the callers had to
respect; a linear scan of the arrays says the same in ten lines.
Japanese was never dispatched through the Lang table: dotrans and
transstr both special-cased it into transjp, which edited Im in place
and wrote commits through a side argument, while transko popped and
cleared a pre that every caller overwrote anyway, and Vietnamese kept
its key history in dotrans. Emit now carries the new raw state next to
the new pre; transjp, transko and transvi are pure functions of (Im,
key), and dotrans and transstr have a single path. Vietnamese history
bookkeeping lives in vi.c, where the full-history flush no longer
resets the caret as a side effect; istone was toneidx() >= 0.
