Complete the word being typed with a public-domain suggestion strip

[RioPlay]

The public's number-one keyboard ask — working word assistance — lands as the mockup's suggestion strip, with completion-only behavior that cannot silently change text:

• A frequency-ordered English word list derived solely from public-domain Project Gutenberg texts via a reproducible script (mobile/android/tools/build_wordlist.py; 10,989 words). Two popular frequency lists were evaluated and rejected on license grounds (LDC-derived corpus data with no redistribution rights; details recorded in the plan doc and NOTICE.txt).
• SuggestionEngine offers up to 3 prefix completions of the current word, case-adapted (first-char and ALL-CAPS). The composing word itself is excluded when it is an exact entry. No auto-correction, no learning, no network.
• The strip renders below the toolbar with stable height, refreshes on commits/delete/navigation/space/Enter, and hides on symbol pages and when the new Suggestions preference (Typing assistance, on by default) is off. It never appears on password fields, raw TYPE_NULL fields, or in private drafts.
• Tapping a chip runs one balanced editor transaction: batch edit → delete the verified composing run → insert the candidate → re-insert the original if the insert fails. The composing word is re-verified at tap time, so caret movement after rendering can never delete unrelated text. The before-cursor read is bounded (≤32 code points); no document access.

Verification (UtterleafFoundation35, API 35): JVM engine tests (rank/case/exclusion/bounds) and wordlist validation; live-IME tests proving strip completion through the real editor and the preference/password/raw gates; 32 focused regression tests across persistence, tuning, geometry, backspace-selection, compose and editor-contract classes; lint 0 errors; 16 tooling tests including the new wordlist validator.

Implemented by opencode (openrouter/z-ai/glm-5.3-flash) in T3 Code.