quest(m0): a broadcast source's sound glides onto a moved delay

quest/m0/pin-bus-stretch.md

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+# [S] A broadcast source's sound glides onto a moved delay
+
+## Goal
+
+The `moq` submodule includes moq-audio's stretching `Positioned` channel, from
+[The bus stretches positioned audio onto its clock](https://github.com/moq-dev/moq/blob/main/quest/m1/audio-jitter-target/bus-stretch.md),
+and a broadcast source's playout (`rs/moq-scene/src/playout.rs`) writes
+through it with a stretch bound, so its sound glides onto a moved playout
+delay as `moq play`'s does. A step of the jitter target no longer writes
+silence into the program's sound or skips it. `README.md`'s broadcast-source
+paragraph says how a delay change sounds.
+
+## Plan
+
+Decided 2026-11-12 (maintainer, /quest-plan), after
+[moq-dev/studio#144](https://github.com/moq-dev/studio/pull/144) kept a
+target step's gap or skip (its follow-up): moq-audio's bus stretches, since
+audio mixing is moq's (`AGENTS.md`'s Upstream), and this quest pins it. ✅ m0,
+beside the other pins (rejected: m2).
+
+Advance with `just upgrade-moq` in its own PR, fixing whatever the new API
+breaks here. Playout's `Writer` (`rs/moq-scene/src/playout.rs`) changes with
+it: today it cuts the part of a frame overlapping the last one and lets a
+later position leave a gap, so a step down would still skip audio. With a
+bound it writes each frame after the last and hands the channel the position
+it is due at, for the channel to converge on. Take the bound `moq play` defaults to (2 s, its `--stretch`)
+unless a measurement here argues for another, and say which in the PR.
+
+## Waiting
+
+- moq-dev/moq: the upstream quest above lands. Check: that quest's PR has
+  merged on moq's `main`, deleting its file, and `moq_audio::bus::Positioned`
+  there takes a stretch bound. A quest file that moved, or went away without
+  its work landing, does not count.
+
+## Required
+
+- [The studio is caught up to moq's main](/quest/m0/pin-main.md) - moq's breaking changes since moq-dev/moq#8272, so this pin takes only its own