sync: keep uvc flowing with delayed audio

AGENTS.md

@@ -140,6 +140,7 @@ Context: the mirrored browser probe finally reproduced the real failure class on
 - [x] Raise calibration offset limits to cover one-second healing without rejecting measured probe corrections.
 - [x] Update the MJPEG/UVC factory audio baseline from `-45ms` to `+720ms` based on the first trustworthy mirrored browser probe artifact.
 - [x] Migrate untouched legacy `-45ms` factory/env calibration files on load so old installs actually receive the new baseline.
+- [x] Make the video/audio-master wait offset-aware so a positive audio playout delay does not freeze UVC video while UAC sleeps before emission.
 - [ ] Flush/stop UAC cleanly on session close, replacement, and recovery.
 - [x] Add tests or contract coverage for bounded UAC settings where practical.
 
@@ -165,5 +166,7 @@ Context: the mirrored browser probe finally reproduced the real failure class on
   - 0.16.18 captured real colored/audio-coded events but the analyzer still bailed with `need at least 3 matching coded pulse pairs; saw 1`. Replaying that artifact after analyzer hardening now reports `gross_failure`: 16/16 coded pairs, p95 `775.7 ms`, activity start `-766.4 ms`, and drift `-2.8 ms`; the failure is stable audio-ahead/video-late skew, not random detector noise.
   - 0.16.19 changes the shipped MJPEG/UVC audio playout baseline to `+720ms`; the next mirrored browser probe should move the measured median from about `-766ms` toward roughly `-46ms` before fine calibration.
   - 0.16.19 mirrored browser probe did not move the measured skew: p95 `885.7 ms`, median `-788.4 ms`, activity start `-659.1 ms`, drift `-81.2 ms`. SSH inspection showed Theia was on commit `c348597`, but `/etc/lesavka/server.env` still contained `LESAVKA_UPSTREAM_AUDIO_PLAYOUT_OFFSET_US=-45000`; the new `+720ms` baseline was not actually installed. Patch the installer to migrate leaked legacy ambient `-45000` to `+720000` unless `LESAVKA_INSTALL_UPSTREAM_AUDIO_PLAYOUT_OFFSET_US` explicitly asks for the legacy value.
+  - 0.16.20 installed the `+720ms` offset (`/etc/lesavka/server.env` had `LESAVKA_UPSTREAM_AUDIO_PLAYOUT_OFFSET_US=720000`), but the mirrored browser capture contained no recognizable color pulses. Theia server logs showed repeated `upstream video frame dropped because the audio master never caught up inside the pairing window`; UVC was effectively starved by the positive audio delay instead of flowing delayed-but-fresh frames.
+  - 0.16.21 makes that wait offset-aware and adds a regression test proving a configured positive audio delay does not freeze UVC video while UAC sleeps before playout.
 - [ ] Re-run the mirrored browser probe after the pre-start false-positive fix.
 - [ ] Run Google Meet manual validation.

Cargo.lock

@@ -1652,7 +1652,7 @@ checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
 [[package]]
 name = "lesavka_client"
-version = "0.16.20"
+version = "0.16.21"
 dependencies = [
  "anyhow",
  "async-stream",
@@ -1686,7 +1686,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_common"
-version = "0.16.20"
+version = "0.16.21"
 dependencies = [
  "anyhow",
  "base64",
@@ -1698,7 +1698,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_server"
-version = "0.16.20"
+version = "0.16.21"
 dependencies = [
  "anyhow",
  "base64",

client/Cargo.toml

@@ -4,7 +4,7 @@ path                    = "src/main.rs"
 
 [package]
 name                    = "lesavka_client"
-version                 = "0.16.20"
+version                 = "0.16.21"
 edition                 = "2024"
 
 [dependencies]

common/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name                    = "lesavka_common"
-version                 = "0.16.20"
+version                 = "0.16.21"
 edition                 = "2024"
 build                   = "build.rs"
 

server/Cargo.toml

@@ -10,7 +10,7 @@ bench                   = false
 
 [package]
 name                    = "lesavka_server"
-version                 = "0.16.20"
+version                 = "0.16.21"
 edition                 = "2024"
 autobins                = false
 

server/src/upstream_media_runtime.rs

@@ -87,6 +87,14 @@ impl UpstreamMediaRuntime {
             }
         }
     }
+
+    fn positive_audio_delay_allowance_us(&self) -> u64 {
+        let camera_offset_us = self.camera_playout_offset_us.load(Ordering::Relaxed);
+        let microphone_offset_us = self.microphone_playout_offset_us.load(Ordering::Relaxed);
+        microphone_offset_us
+            .saturating_sub(camera_offset_us)
+            .max(0) as u64
+    }
 }
 
 include!("upstream_media_runtime/lease_lifecycle.rs");
@@ -132,6 +140,7 @@ impl UpstreamMediaRuntime {
         let slack_us = upstream_pairing_master_slack()
             .as_micros()
             .min(u64::MAX as u128) as u64;
+        let audio_delay_allowance_us = self.positive_audio_delay_allowance_us();
         loop {
             let notified = self.audio_progress_notify.notified();
             {
@@ -143,7 +152,10 @@ impl UpstreamMediaRuntime {
                     return true;
                 }
                 if state.last_audio_local_pts_us.is_some_and(|audio_pts_us| {
-                    audio_pts_us.saturating_add(slack_us) >= video_local_pts_us
+                    audio_pts_us
+                        .saturating_add(slack_us)
+                        .saturating_add(audio_delay_allowance_us)
+                        >= video_local_pts_us
                 }) {
                     return true;
                 }

server/src/upstream_media_runtime/tests/async_wait.rs

@@ -1,4 +1,4 @@
-use super::{UpstreamMediaRuntime, play};
+use super::{UpstreamMediaRuntime, play, runtime_without_offsets};
 use serial_test::serial;
 use std::sync::Arc;
 use std::time::Duration;
@@ -6,7 +6,7 @@ use std::time::Duration;
 #[tokio::test(flavor = "current_thread")]
 #[serial(upstream_media_runtime)]
 async fn wait_for_audio_master_releases_video_once_audio_catches_up() {
-    let runtime = Arc::new(UpstreamMediaRuntime::new());
+    let runtime = Arc::new(runtime_without_offsets());
     let _camera = runtime.activate_camera();
     let _microphone = runtime.activate_microphone();
 
@@ -34,8 +34,36 @@ async fn wait_for_audio_master_releases_video_once_audio_catches_up() {
 
 #[tokio::test(flavor = "current_thread")]
 #[serial(upstream_media_runtime)]
-async fn wait_for_audio_master_times_out_when_audio_never_catches_up() {
+async fn wait_for_audio_master_allows_configured_positive_audio_delay() {
     let runtime = Arc::new(UpstreamMediaRuntime::new());
+    runtime.set_playout_offsets(0, 720_000);
+    let _camera = runtime.activate_camera();
+    let _microphone = runtime.activate_microphone();
+
+    assert!(matches!(
+        runtime.plan_video_pts(1_000_000, 16_666),
+        super::UpstreamPlanDecision::AwaitingPair
+    ));
+    let _audio_first = play(runtime.plan_audio_pts(1_000_000));
+    let _video_first = play(runtime.plan_video_pts(1_000_000, 16_666));
+    let delayed_video = play(runtime.plan_video_pts(1_700_000, 16_666));
+
+    assert_eq!(delayed_video.local_pts_us, 700_000);
+    assert!(
+        runtime
+            .wait_for_audio_master(
+                delayed_video.local_pts_us,
+                tokio::time::Instant::now() + Duration::from_millis(5)
+            )
+            .await,
+        "a positive audio playout offset should not freeze UVC video while the audio sink sleeps"
+    );
+}
+
+#[tokio::test(flavor = "current_thread")]
+#[serial(upstream_media_runtime)]
+async fn wait_for_audio_master_times_out_when_audio_never_catches_up() {
+    let runtime = Arc::new(runtime_without_offsets());
     let _camera = runtime.activate_camera();
     let _microphone = runtime.activate_microphone();