Follow-up hardening from two review passes on the on-device translation
feature:
- Privacy (HIGH): the translation cache is decrypted message plaintext,
but logout did not clear it (unlike the search index), leaving up to
300 cleartext bodies in localStorage on shared devices. Add
clearTranslationCache() and call it from both logout paths
(logoutClient and the server-forced SessionLoggedOut handler).
- Edited messages (MEDIUM): the cache key was eventId:target with no
content dependence, so an edit reused the pre-edit translation. Fold a
content fingerprint into the key, and re-arm the auto-translate
one-shot when the text changes.
- Settings (LOW): coerce a persisted translateTargetLang to a supported
curated code so the hook never targets a language the engine can't
produce (previously only the UI clamped it).
- Chinese (LOW): restore canonical BCP-47 case (zh-Hant / zh-Hans) at
the Translator API boundary, since normalizeLang lowercases the script
subtag for internal keys.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Add per-message translation that runs entirely on-device via the
Chromium built-in Translator + LanguageDetector APIs. Message text
never leaves the machine and never touches a cloud service, preserving
the E2EE guarantee. When the on-device engine is unavailable
(non-Chromium / mobile) the feature simply hides itself; there is no
network fallback.
- Engine abstraction (utils/translation): TranslationEngine interface
plus a chromeTranslationEngine implementation (feature-detected,
caches translator/detector instances, download-progress monitor).
Pure lang-code helpers (normalize/sameLanguage/curated targets) with
unit tests.
- Settings: translateTargetLang (default English) + autoTranslate
(opt-in), with a Messages settings tile — a target-language select
and an auto-translate switch, disabled with a note where unsupported.
- useMessageTranslation hook + shared per-event toggle atom-family and a
persisted LRU cache so scrollback never re-translates.
- UI: a Translate / Show Original message-menu action, an inline
"Translated from <lang> - Show original" chip, and a body swap in
m.text/m.emote/m.notice that renders the translated text through the
plain-text path (linkify + emoji) inside a dir=auto span for RTL.
- Auto-translate flips foreign messages whose model is already
downloaded; first-time downloads keep the manual chip (user gesture).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
jaredandClaude Opus 4.8