* Fix CJK IME input not working (#118)
CJK (Korean, Japanese, Chinese) IME input was completely broken because
cmux never forwarded preedit/composition state to Ghostty's libghostty.
Root causes and fixes:
1. Missing preedit sync: Added syncPreedit() that calls
ghostty_surface_preedit() to notify Ghostty about IME composition
text. Called from setMarkedText, unmarkText, and after
interpretKeyEvents in keyDown.
2. Wrong composing flag: The composing flag on key events now correctly
accounts for when composition just ended (markedTextBefore was true
but markedText is now empty), preventing spurious deletions when
canceling composition.
3. Event interception during IME: Added early exits in
performKeyEquivalent, the NSWindow swizzle, and the local event
monitor (handleCustomShortcut) to avoid stealing key events while
IME has active marked text.
4. IME popup positioning: firstRect(forCharacterRange:) now uses
ghostty_surface_ime_point() for accurate cursor-relative positioning
of the IME candidate window.
* Add regression tests for CJK IME composition (#118)
31 tests covering Korean, Japanese, and Chinese IME input scenarios:
- Korean jamo combining: ㅎ -> 하 -> 한 composition lifecycle
- Chinese pinyin: multi-letter marked text and candidate selection
- Japanese hiragana-to-kanji: romaji -> hiragana -> kanji conversion
- insertText correctly commits composed text and clears marked state
- unmarkText properly clears composition state (idempotent)
- performKeyEquivalent returns false during active composition for
all key types (plain, shift, space, return, escape)
- Shortcut bypass: hasMarkedText gates the handleCustomShortcut bypass
- Multi-syllable sequences, backspace correction, and rapid transitions
- keyTextAccumulator lifecycle tests
Also adds #if DEBUG test accessors for keyTextAccumulator on
GhosttyNSView to enable unit testing the accumulator path.
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