quest: delete opus-dtx-timestamps after a measured no-go, plan usedtx removal

quest/m1/README.md

@@ -51,7 +51,6 @@ blocks. The quests that gated m0 lines moved under them.
 - [Delete the live marker](/quest/m1/announce-live-removal.md) - announce streams yield only route events; the `Live` marker and its hold machinery are gone
 - [WebTransport close backends](/quest/m1/wt-close-backends.md) - web-transport-noq and -quinn keep the session alive while closing, and iroh's client reads a capsule close
 - [Enabled flag](/quest/m1/catalog-enabled.md) - one `enabled` rendition flag replaces `stalled` and pausing, and the flapping encoder-lag detector is deleted
-- [DTX timestamps](/quest/m1/opus-dtx-timestamps.md) - Opus DTX keeps the capture timeline, so voice enables it by default again
 - [Spent capture budget errors](/quest/m1/capture-exhausted-error.md) - a camera or microphone that runs out of retries sets `out.error` instead of failing silently
 - [SUBSCRIBE_DROP](/quest/m1/subscribe-drop.md) - every stream group in a lite subscription arrives or is dropped by name, and lite-07 drops its stream count for it
 - [#2991](/quest/m1/2991-net-coalesce-dynamic-tracks-and-preserve-sequences-across.md) - one dynamic producer per track name in both languages, with the sequence namespace surviving a replacement
@@ -74,6 +73,7 @@ blocks. The quests that gated m0 lines moved under them.
 - [Auth client CA](/quest/m1/relay-auth-client-ca.md) - `auth::Config::validate` and `init` take the client-CA flag, so no caller can skip the check
 - [TS stats module](/quest/m1/ts-stats-module.md) - the TS stats types move under `ts::stats` as `Snapshot` and `Stream`, with an owned `track`
 - [Audio capture without ALSA link](/quest/m1/capture-alsa-link.md) - moq-audio capture and playback build on Linux without linking libasound
+- [Remove Opus DTX](/quest/m1/opus-usedtx-removal.md) - `@moq/publish` drops `usedtx`, since Chromium shifts the capture timeline under DTX
 - [Capture by default](/quest/m1/capture-default.md) - moq-video and moq-audio build `capture` by default, so pre-merge checks test it and the capture gate goes away
 - [Ship capture and playback](/quest/m1/cli-packaging.md) - a released moq binary can capture and play, which no distribution currently enables
 - [Deploy moq.sh](/quest/m1/moq-sh-deploy.md) - the first manual deploy serves the installer at moq.sh, and the first `release` run proves the CI token

quest/m1/opus-usedtx-removal.md

@@ -0,0 +1,27 @@
+# [XS] Remove Opus DTX from @moq/publish
+
+## Goal
+
+`OpusConfig.usedtx` is gone from `@moq/publish`, and the demo's DTX checkbox
+with it, so no publisher can turn on browser Opus DTX. Breaking for
+`@moq/publish`.
+
+## Plan
+
+Decided 2026-10-06 after the measured no-go in
+[#4902](https://github.com/moq-dev/moq/pull/4902): with DTX on, Chromium
+stamps each Opus chunk as the first input's timestamp plus the samples it
+emitted, so every suppressed frame pulls later chunks earlier (14 s of input
+ended at 8.9 s). No WebCodecs output (duration, metadata, `flush()`, Ogg)
+recovers the dropped span, and Chromium's decoder collapses timestamp gaps on
+the listener too. Firefox keeps the timeline; Safari ignores `usedtx`.
+
+- Remove `usedtx` from `OpusConfig` (`js/publish/src/audio/encoder.ts`) and
+  its test, and the checkbox and `opusDtx` signal in `demo/web/src/publish.ts`
+  and `publish.html`.
+- Update `doc/lib/js` wherever it names the option.
+- Silence suppression for voice, if a customer ever wants it, is new work:
+  encode without DTX and skip silent frames with our own voice detection, or a
+  WASM libopus encoder ([Opus backend](/quest/m2/audio-opus-backend.md)).
+
+Public API: removes `OpusConfig.usedtx` from `@moq/publish`. Wire: none.