[BUG] Windows desktop: composer dictation randomly duplicates whole sentences (intermittent), mic auto-stops after ~1 min

Summary

Voice dictation in the Windows desktop app (Code tab chat box) randomly inserts whole sentences or clauses twice, back to back, before the message is sent. Intermittent: some messages are clean, others doubled, with no visible pattern. Related to #77771 (same symptom on macOS, marked stale) — this is a current Windows report.

Environment

• Claude desktop app for Windows, Code tab, built-in microphone in the chat composer (not the Claude Panel / not Windows voice typing)
• Windows 11 Pro 10.0.26200
• English (US) dictation
• Seen repeatedly on Sept 19–20, 2026

What happens

Spoken once:

"And I'm looking to see if that's in effect. So I don't want to add any more stuff. To get it now mixed up with the current stuff we're working on. So we'll wait until what we have pending is released."

Text that landed in the composer (verbatim, sent at ~13:40 ET on 2026-09-20):

"And I'm looking to see if that's in effect. So I don't want to add any more stuff. To get it now mixed up with the current stuff, we're working on. So we'll wait until what we have pending is released. Hopefully your recommendation works.. And I'm looking to see if that's in effect. So I don't want to add any more. Stuff. To get it now mix up with the current stuff we're working on. So we'll wait until what we have pending is released. Then we'll go into. Hopefully that works. Hopefully your recommendation works and we won't have to do anything else."

Earlier example the same morning: a two-sentence block ("I have had nothing new to date. You cannot convince me that there is no traffic.") arrived twice in a row.

Expected

Each spoken phrase appears once.

Also observed

The composer microphone switches itself off after roughly a minute of silence, with no indication, so the tail of a slow sentence is lost.

Notes

• The user's own web-based dictation pad (Web Speech API in Chrome) does not show this on the same PC and mic, so it is not the microphone or the OS.
• Happens with the composer empty and with existing text; the duplicate is appended after the original, not interleaved.
• Filed on behalf of the account owner at his request.