fix(audio-quality): flush the build before the first row

quest/m1/audio-jitter-target/README.md

@@ -36,10 +36,10 @@ the native decode path too, asserting the same target series the browser's
 
 ## Required
 
-- [Opus isolated-ring target](/quest/m1/audio-jitter-target/opus-isolated-target.md) - the isolated ring holds the target at near-zero jitter
 - [Audio rename](/quest/m1/audio-jitter-target/audio-rename.md) - a renamed audio track continues the outgoing arrival estimate, so playback neither skips nor stalls
 - [Watch](/quest/m1/audio-jitter-target/watch.md) - the browser's measured target, proven on Chrome and Safari against the public relay
 - [AAC bursty budgets](/quest/m1/audio-jitter-target/aac-bursty-budgets.md) - post-fix nightlies confirm AAC no longer re-stalls, and its budgets are tightened from them
+- [Opus near-zero budgets](/quest/m1/audio-jitter-target/opus-near-zero-budgets.md) - post-flush nightlies confirm the first row no longer stalls, and its budgets are tightened from them
 
 ## Closes
 

quest/m1/audio-jitter-target/opus-near-zero-budgets.md

@@ -0,0 +1,32 @@
+# [XS] Tighten the Opus near-zero browser budgets after the build flush
+
+## Goal
+
+Seven scheduled nightlies on `main` after the harness began flushing its build
+before the first row show the Opus `near-zero` `isolated` row holding the
+same 60 ms target as the `plain` row with no underrun episodes, and
+`test/audio-quality/budgets.json` carries ceilings re-measured from them.
+
+## Plan
+
+Waits on the nightlies: check the `audio-quality-run` artifacts of the
+scheduled Nightly runs on `main` (`gh run download <id> -n audio-quality-run`)
+once seven have run since the fix merged. Never dispatch the nightly by hand.
+
+The stall was never the isolated ring. That row is simply the matrix's first,
+and a cold `cargo build` left about 800 MB dirty when it started. On the ARM
+runner each periodic writeback burst (100 to 280 MB, about 10 s apart) froze
+the page's main thread for 100 to 320 ms until the backlog drained, about 30 s
+in. A branch experiment put the plain ring first after a cold build, and it
+failed the same way (540 ms target, the same 10 s long-task clusters).
+Isolated-first, with the build flushed beforehand, held 60 ms.
+
+Re-measure the Opus near-zero rows by the rule in the budgets note, and drop
+the note's sentence that budgets the isolated row's one-second drops as
+measured. If the first row still shows long-task clusters, compare
+`<tag>.longtasks.json` against the runner's disk activity before changing the
+player.
+
+## Related
+
+- [AAC bursty budgets](/quest/m1/audio-jitter-target/aac-bursty-budgets.md) - the same re-measure for the AAC rows, on its own fix's nightlies

quest/m1/audio-jitter-target/watch.md

@@ -55,11 +55,8 @@ Decided 2026-10-15: keep this proof in m1 with the existing playback and
 A/V clock work. The estimator defaults on; deferring watch-worker does not
 defer validation of the current player.
 
-## Required
-
-- [Opus isolated-ring target](/quest/m1/audio-jitter-target/opus-isolated-target.md) - the isolated ring holds the target at near-zero jitter
-
 ## Related
 
 - [A/V clock](/quest/m1/av-clock.md) - reshapes `SyncInput` around the per-track target this line produces
 - [AAC bursty budgets](/quest/m1/audio-jitter-target/aac-bursty-budgets.md) - confirms the AAC reorder fix on the nightlies, no gate on this proof
+- [Opus near-zero budgets](/quest/m1/audio-jitter-target/opus-near-zero-budgets.md) - confirms the build-flush fix on the nightlies, no gate on this proof

quest/m1/browser-rename-check.md

@@ -59,4 +59,4 @@ racing the old track's finish (`stream aborted by the remote server`).
 
 - [Rust identity enforcement](/quest/m1/catalog-identity-rs.md) - the same contract for the Rust publishers
 - [Capture channel count and cold-start tone](/quest/m1/publish-audio-channel-count.md) - already owns the unpinned cold-start audio-tone symptom
-- [Isolated Opus target](/quest/m1/audio-jitter-target/opus-isolated-target.md) - related playout stalls, with no shared cause established
+- [Isolated Opus target (#5807)](https://github.com/moq-dev/moq/pull/5807) - related playout stalls, with no shared cause established

test/audio-quality/run.sh

@@ -243,6 +243,12 @@ if [[ ${#ROWS[@]} -gt 0 ]]; then
         bunx vite build --outDir "$HARNESS_RUN/page" --emptyOutDir
     )
 
+    # A cold build leaves hundreds of MB dirty, and on the nightly runner each periodic writeback
+    # burst stalls the page's main thread for ~300 ms, so the first row would grade the build's
+    # flush instead of the player. Flush it before any row plays.
+    echo "flushing the build to disk..."
+    sync
+
     # ── relay ───────────────────────────────────────────────────────────────
     harness_port relay
     RELAY_PORT="$HARNESS_PORT"