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F07 — IME / text input ​

The hardest row in the matrix. Composed text input (CJK, and increasingly emoji/voice input) arrives through a second, stateful channel that must be interleaved with raw key events: pre-edit strings, candidate windows anchored to the caret, commit/replace semantics. Every platform has a different protocol; several have two.

Requirements ​

  1. Render an editable line of text with a visible caret. Display the pre-edit string inline at the caret with underline styling, distinct from committed text.
  2. Report the cursor rectangle to the IME so the candidate window anchors to the caret (and re-report as the caret moves — prove it by typing at both ends of a long line):
    • Wayland: zwp_text_input_v3 — set_cursor_rectangle, handle preedit_string, commit_string, delete_surrounding_text; enable on focus.
    • Win32: TSF (ITfThreadMgr/ITextStoreACP) — if the COM surface proves impractical from plain D within the budget, fall back to IMM32 (WM_IME_COMPOSITION, ImmSetCandidateWindow) and document precisely why TSF was impractical.
    • macOS: implement NSTextInputClient on the view (setMarkedText:…, firstRectForCharacterRange:…, insertText:replacementRange:).
    • X11: XIM (XOpenIM, XCreateIC with XIMPreeditPosition) — document its pathologies (synchronization, server restarts, locale coupling) first-hand.
  3. Handle the full lifecycle: focus in/out mid-composition (what happens to the pre-edit?), commit, cancel (Esc), and replacement of surrounding text.
  4. Log every IME event with payloads (preedit text=… cursor=…, commit text=…, delete_surrounding before=… after=…).

Findings to record ​

  • The event choreography per platform for: typing "nihao" + space with a Pinyin IME; cancel mid-composition; focus loss mid-composition.
  • How key events and text events interleave (which key events are swallowed).
  • Candidate-window positioning units (logical vs physical — feeds F08).
  • The TSF-vs-IMM32 decision record (or the COM bring-up notes if TSF worked).

Verification ​

Tier C is the truth for this row — it needs a real CJK IME (fcitx5/ibus on Linux, the built-in Pinyin IME on Windows/macOS). Each demo ships a precise manual script (input method to enable, keystrokes, expected pre-edit/commit logs). Agent-side (Tier A) verification is limited to: the protocol handshake under headless weston (zwp_text_input_v3 advertised?), XIM bring-up under Xvfb with XMODIFIERS=@im=none fallback behavior, and compile-level correctness elsewhere. Budget note: this row gets the strongest agents.