[BUG] Korean IME: cursor fails to advance after each composed syllable; stray line breaks mid-word (v2.1.220, Windows)

Summary

After a recent update, Korean (Hangul) IME typing in the Claude Code CLI input box behaves abnormally: the cursor does not advance after a syllable is composed — it stays in place, then jumps one cell only when the next syllable starts. Line wrapping has also become erratic: stray line breaks are inserted mid-word while typing continuously.

The user describes it as: "한 글자 치고 나면 한 칸씩 나가지지 않고 제자리에 있다가 두 번째 글자에서 또 한 칸 넘어간다. 한 줄씩 이어쓰는데 칸 바꾸기(줄바꿈)가 이상해졌다."

Notably, text the user submitted while the bug was active came through with spurious newlines inserted between Hangul syllables mid-sentence, e.g.:

한
글짜 치고 나면 한 
칸씩 나가지지 않고 제 자리에 
있다가 두
번째 
글짜에서 또 한칸 넘어간다.

This started recently ("became strange after an update") — it did not happen before.

Symptom details

• While composing Hangul with the Korean IME, the visible cursor stays on the current cell after the syllable is committed; it advances only when the following syllable's first jamo is typed.
• During continuous typing, the input line wraps/breaks at wrong positions, and submitted text contains unintended line breaks between syllables.
• English/ASCII typing is unaffected.
• Only the Claude Code CLI prompt is affected — other CLI programs in the same terminal behave normally with the same IME.

Environment

• Claude Code: 2.1.220 (native build), Node v24.14.1
• OS: Windows 11 Pro, build 10.0.26200
• IME: Windows built-in Korean IME (2-beolsik)
• Terminal: Orca desktop app (Electron-based terminal panes; StablyAI.Orca 1.4.163). Windows Terminal 1.24.11911.0 is installed but this symptom has not yet been re-tested there — will follow up with a repro check in Windows Terminal / plain conhost if useful.

Possibly related (but different symptom)

• #77401 (composition characters intermittently dropped) — different: nothing is dropped here, the cursor lags one syllable behind.
• #70007 (syllables decompose into jamo) — not observed here.
• #73064 (한/영 toggle ignored) — toggle works here.

Expected

Cursor advances by the character's display width immediately when a Hangul syllable is committed, and no stray line breaks are inserted during continuous typing.