[Bug] Non-CJK text (Russian) also corrupted during streaming — syllables lost/duplicated, state.db is intact, restart fixes it

Describe the bug

Hermes Desktop (Windows) renders assistant messages with lost or duplicated fragments (individual syllables) during/after streaming. The corruption affects not only CJK — the same happens with Russian / Cyrillic text.

• In the visible chat bubble, part of a word's syllable goes missing, then later repeats.
• The same text is always complete in state.db — read it back and the message is intact. The corruption is purely a render-layer merge bug.
• Restarting the app (or reloading the session) makes the identical text render correctly.

Only the chat message content is affected; the rest of the UI is fine.

Example (Russian)

Rendered in bubble	Actual (state.db)
«Чтолось»	«Что осталось»
«Имп схем НЕ построен»	«Импорт схем НЕ построен»
«точню направление»	«Уточню направление»
«Вече Новода»	«Вече Новгорода»

Root cause (likely)

This is the same mechanism as #793 (CJK), which I reproduce here for non-CJK:

mergeStreamedWithFinal() in src/renderer/src/screens/Chat/dashboardEventAdapter.ts reconciles the streamed text against final_response at end of stream via isLossyChunkCopy() (lossyText.ts). That uses a greedy indexOf over repeating fragments — for any text containing repeated substrings (common in Russian too), it matches the wrong position → false "lost block" → overwrites the streamed text with an incomplete final → characters get dropped/duplicated. commonSuffixLength() boundary handling is inexact for mixed-script text.

Suggested fix: make isLossyChunkCopy match forward from j with exact-boundary/character-level verification (currently full.indexOf(probe, j)), or skip the lossy reconciliation branch and do a simple final ⊇ streamed containment check.

Related

• #793 — same CJK text-corruption root cause
• #508 — merged fix for duplicate/split turns (message ordering), does not fix character-level loss
• #550 / #517 / #527 — duplicate-message family, also not this

Expected vs actual

Expected: streamed text merges into the identical content that lands in state.db. Actual: visible bubble shows corrupted (lost/duplicated characters) while state.db holds the full correct text.

Steps to reproduce: any long-assistant-turn chat with the desktop app on a Russian-language model; corruption appears during/after streaming, disappears on app restart.

Desktop bundle can lag behind hermes-agent source — worth verifying against current main too.