diff --git a/Cargo.lock b/Cargo.lock
index b8dbc29..40235a4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1652,7 +1652,7 @@ checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
 [[package]]
 name = "lesavka_client"
-version = "0.16.11"
+version = "0.16.12"
 dependencies = [
  "anyhow",
  "async-stream",
@@ -1686,7 +1686,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_common"
-version = "0.16.11"
+version = "0.16.12"
 dependencies = [
  "anyhow",
  "base64",
@@ -1698,7 +1698,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_server"
-version = "0.16.11"
+version = "0.16.12"
 dependencies = [
  "anyhow",
  "base64",
diff --git a/client/Cargo.toml b/client/Cargo.toml
index 3c8d722..60ab076 100644
--- a/client/Cargo.toml
+++ b/client/Cargo.toml
@@ -4,7 +4,7 @@ path                    = "src/main.rs"
 
 [package]
 name                    = "lesavka_client"
-version                 = "0.16.11"
+version                 = "0.16.12"
 edition                 = "2024"
 
 [dependencies]
diff --git a/client/src/bin/lesavka-sync-analyze.rs b/client/src/bin/lesavka-sync-analyze.rs
index ff8e60c..fd5f002 100644
--- a/client/src/bin/lesavka-sync-analyze.rs
+++ b/client/src/bin/lesavka-sync-analyze.rs
@@ -123,6 +123,7 @@ A/V sync report for {capture}
 - video onsets: {video_events}
 - audio onsets: {audio_events}
 - paired pulses: {paired_events}
+- activity start delta: {activity_start_delta:+.1} ms (audio after video is positive)
 - first skew: {first_skew:+.1} ms (audio after video is positive)
 - last skew: {last_skew:+.1} ms
 - mean skew: {mean_skew:+.1} ms
@@ -142,6 +143,7 @@ A/V sync report for {capture}
         video_events = report.video_event_count,
         audio_events = report.audio_event_count,
         paired_events = report.paired_event_count,
+        activity_start_delta = report.activity_start_delta_ms,
         first_skew = report.first_skew_ms,
         last_skew = report.last_skew_ms,
         mean_skew = report.mean_skew_ms,
diff --git a/client/src/sync_probe/analyze/onset_detection/correlation.rs b/client/src/sync_probe/analyze/onset_detection/correlation.rs
index 087b4e8..b86290a 100644
--- a/client/src/sync_probe/analyze/onset_detection/correlation.rs
+++ b/client/src/sync_probe/analyze/onset_detection/correlation.rs
@@ -33,6 +33,7 @@ pub(super) fn correlate_onsets(
         bail!("pulse period must stay positive");
     }
 
+    let activity_start_delta_ms = (audio_onsets_s[0] - video_onsets_s[0]) * 1000.0;
     let (video_onsets_s, audio_onsets_s, common_window) =
         trim_onsets_to_common_activity_window(video_onsets_s, audio_onsets_s, max_pair_gap_s);
     let expected_start_skew_ms = (audio_onsets_s[0] - video_onsets_s[0]) * 1000.0;
@@ -69,6 +70,7 @@ pub(super) fn correlate_onsets(
     Ok(sync_report_from_pairs(
         common_window.filter_onsets(video_onsets_s),
         common_window.filter_onsets(audio_onsets_s),
+        activity_start_delta_ms,
         pairs,
     ))
 }
@@ -121,6 +123,7 @@ pub(crate) fn correlate_segments(
         bail!("audio onset list is empty");
     }
 
+    let activity_start_delta_ms = (audio_onsets_s[0] - video_onsets_s[0]) * 1000.0;
     let (video_onsets_s, audio_onsets_s, common_window) =
         trim_onsets_to_common_activity_window(&video_onsets_s, &audio_onsets_s, max_pair_gap_s);
     let expected_start_skew_ms = (audio_onsets_s[0] - video_onsets_s[0]) * 1000.0;
@@ -166,6 +169,7 @@ pub(crate) fn correlate_segments(
     Ok(sync_report_from_pairs(
         video_onsets_s,
         audio_onsets_s,
+        activity_start_delta_ms,
         pairs,
     ))
 }
@@ -433,6 +437,7 @@ pub(super) fn shortest_wrapped_difference(delta_s: f64, pulse_period_s: f64) ->
 fn sync_report_from_pairs(
     video_onsets_s: &[f64],
     audio_onsets_s: &[f64],
+    activity_start_delta_ms: f64,
     pairs: Vec<MatchedOnsetPair>,
 ) -> SyncAnalysisReport {
     let paired_events = pairs
@@ -466,6 +471,7 @@ fn sync_report_from_pairs(
         video_event_count: video_onsets_s.len(),
         audio_event_count: audio_onsets_s.len(),
         paired_event_count: skews_ms.len(),
+        activity_start_delta_ms,
         first_skew_ms,
         last_skew_ms,
         mean_skew_ms,
diff --git a/client/src/sync_probe/analyze/onset_detection/tests.rs b/client/src/sync_probe/analyze/onset_detection/tests.rs
index 32051c9..b807b78 100644
--- a/client/src/sync_probe/analyze/onset_detection/tests.rs
+++ b/client/src/sync_probe/analyze/onset_detection/tests.rs
@@ -234,6 +234,44 @@ fn correlate_segments_validate_inputs_and_support_single_pulse_fallback() {
     assert!(correlate_segments(&video, &audio, 1.0, 0.1, 3, 0.05).is_err());
 }
 
+#[test]
+fn correlate_segments_preserves_whole_period_delay_evidence() {
+    fn segment(start_s: f64, duration_s: f64) -> PulseSegment {
+        PulseSegment {
+            start_s,
+            end_s: start_s + duration_s,
+            duration_s,
+        }
+    }
+
+    let video = (0..30)
+        .map(|tick| segment(f64::from(tick), if tick % 5 == 0 { 0.24 } else { 0.12 }))
+        .collect::<Vec<_>>();
+    let audio = (0..30)
+        .map(|tick| {
+            segment(
+                f64::from(tick) + 20.0,
+                if tick % 5 == 0 { 0.24 } else { 0.12 },
+            )
+        })
+        .collect::<Vec<_>>();
+
+    let report = correlate_segments(&video, &audio, 1.0, 0.12, 5, 0.5).expect("correlated report");
+
+    assert_eq!(report.activity_start_delta_ms, 20_000.0);
+    assert!(
+        report.max_abs_skew_ms < 1.0,
+        "cadence aliasing still creates apparently good pairs"
+    );
+    let verdict = report.verdict();
+    assert_eq!(verdict.status, "catastrophic_failure");
+    assert!(
+        verdict.reason.contains("activity starts"),
+        "unexpected verdict reason: {}",
+        verdict.reason
+    );
+}
+
 fn assert_sync_report_shape(report: &SyncAnalysisReport, paired_events: usize) {
     assert_eq!(report.video_event_count, paired_events);
     assert_eq!(report.audio_event_count, paired_events);
diff --git a/client/src/sync_probe/analyze/report.rs b/client/src/sync_probe/analyze/report.rs
index d2a795c..6a0fa7b 100644
--- a/client/src/sync_probe/analyze/report.rs
+++ b/client/src/sync_probe/analyze/report.rs
@@ -19,6 +19,7 @@ pub struct SyncAnalysisReport {
     pub video_event_count: usize,
     pub audio_event_count: usize,
     pub paired_event_count: usize,
+    pub activity_start_delta_ms: f64,
     pub first_skew_ms: f64,
     pub last_skew_ms: f64,
     pub mean_skew_ms: f64,
@@ -77,6 +78,17 @@ impl SyncAnalysisReport {
             reason: String::new(),
         };
 
+        if self.activity_start_delta_ms.abs() >= VERDICT_CATASTROPHIC_MAX_ABS_SKEW_MS {
+            return SyncAnalysisVerdict {
+                status: "catastrophic_failure".to_string(),
+                reason: format!(
+                    "audio/video activity starts are separated by {:+.1} ms, at or above the {:.1} ms catastrophic boundary",
+                    self.activity_start_delta_ms, VERDICT_CATASTROPHIC_MAX_ABS_SKEW_MS
+                ),
+                ..base
+            };
+        }
+
         if self.paired_event_count < VERDICT_MIN_PAIRED_EVENTS {
             return SyncAnalysisVerdict {
                 status: "insufficient_data".to_string(),
@@ -146,6 +158,18 @@ impl SyncAnalysisReport {
 
     #[must_use]
     pub fn calibration_recommendation(&self) -> SyncCalibrationRecommendation {
+        if self.activity_start_delta_ms.abs() >= VERDICT_ACCEPTABLE_P95_ABS_SKEW_MS {
+            return SyncCalibrationRecommendation {
+                ready: false,
+                recommended_audio_offset_adjust_us: 0,
+                recommended_video_offset_adjust_us: 0,
+                note: format!(
+                    "activity start delta {:+.1} ms exceeds the {:.1} ms calibration-safe band",
+                    self.activity_start_delta_ms, VERDICT_ACCEPTABLE_P95_ABS_SKEW_MS
+                ),
+            };
+        }
+
         if self.paired_event_count < CALIBRATION_MIN_PAIRED_EVENTS {
             return SyncCalibrationRecommendation {
                 ready: false,
@@ -247,6 +271,7 @@ mod tests {
             video_event_count: 4,
             audio_event_count: 4,
             paired_event_count: 4,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 20.0,
             last_skew_ms: 20.0,
             mean_skew_ms: 20.0,
@@ -275,6 +300,7 @@ mod tests {
             video_event_count: 12,
             audio_event_count: 12,
             paired_event_count: 12,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 10.0,
             last_skew_ms: 70.0,
             mean_skew_ms: 40.0,
@@ -299,6 +325,7 @@ mod tests {
             video_event_count: 14,
             audio_event_count: 14,
             paired_event_count: 12,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 28.0,
             last_skew_ms: 32.0,
             mean_skew_ms: 30.0,
@@ -324,6 +351,7 @@ mod tests {
             video_event_count: 14,
             audio_event_count: 14,
             paired_event_count: 12,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 3.0,
             last_skew_ms: 4.0,
             mean_skew_ms: 3.5,
@@ -348,6 +376,7 @@ mod tests {
             video_event_count: 5,
             audio_event_count: 5,
             paired_event_count: 5,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 10.0,
             last_skew_ms: 20.0,
             mean_skew_ms: 15.0,
@@ -371,6 +400,7 @@ mod tests {
             video_event_count: 5,
             audio_event_count: 5,
             paired_event_count: 5,
+            activity_start_delta_ms: 0.0,
             first_skew_ms: 8_000.0,
             last_skew_ms: 8_000.0,
             mean_skew_ms: 8_000.0,
@@ -387,4 +417,29 @@ mod tests {
         assert!(!verdict.passed);
         assert_eq!(verdict.status, "catastrophic_failure");
     }
+
+    #[test]
+    fn verdict_flags_catastrophic_activity_start_delta() {
+        let report = SyncAnalysisReport {
+            video_event_count: 20,
+            audio_event_count: 20,
+            paired_event_count: 20,
+            activity_start_delta_ms: 20_000.0,
+            first_skew_ms: 0.0,
+            last_skew_ms: 0.0,
+            mean_skew_ms: 0.0,
+            median_skew_ms: 0.0,
+            max_abs_skew_ms: 0.0,
+            drift_ms: 0.0,
+            skews_ms: vec![0.0; 20],
+            video_onsets_s: vec![],
+            audio_onsets_s: vec![],
+            paired_events: vec![],
+        };
+
+        let verdict = report.verdict();
+        assert!(!verdict.passed);
+        assert_eq!(verdict.status, "catastrophic_failure");
+        assert!(verdict.reason.contains("activity starts"));
+    }
 }
diff --git a/common/Cargo.toml b/common/Cargo.toml
index 5a5c5c4..047293e 100644
--- a/common/Cargo.toml
+++ b/common/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name                    = "lesavka_common"
-version                 = "0.16.11"
+version                 = "0.16.12"
 edition                 = "2024"
 build                   = "build.rs"
 
diff --git a/scripts/manual/browser_consumer_probe.py b/scripts/manual/browser_consumer_probe.py
index 90f912e..5018735 100755
--- a/scripts/manual/browser_consumer_probe.py
+++ b/scripts/manual/browser_consumer_probe.py
@@ -177,7 +177,10 @@ async function initStream() {{
     await postJson('/status', {{ page_message: 'permission granted' }});
     const devices = await navigator.mediaDevices.enumerateDevices();
     await postJson('/status', {{ page_message: 'devices enumerated', devices: devices.map(fmtDevice) }});
-    const videoIn = devices.find(d => d.kind === 'videoinput' && /UGREEN/i.test(d.label)) || devices.find(d => d.kind === 'videoinput');
+    const videoIn =
+      devices.find(d => d.kind === 'videoinput' && /(Lesavka Composite|Multifunction Composite Gadget)/i.test(d.label)) ||
+      devices.find(d => d.kind === 'videoinput' && /UGREEN/i.test(d.label)) ||
+      devices.find(d => d.kind === 'videoinput');
     const audioIn = devices.find(d => d.kind === 'audioinput' && /(Multifunction Composite Gadget|Lesavka Composite)/i.test(d.label)) || devices.find(d => d.kind === 'audioinput');
     stream = await navigator.mediaDevices.getUserMedia({{
       video: videoIn ? {{ deviceId: {{ exact: videoIn.deviceId }} }} : true,
diff --git a/scripts/manual/run_upstream_av_sync.sh b/scripts/manual/run_upstream_av_sync.sh
index 29fc4a6..0414c63 100755
--- a/scripts/manual/run_upstream_av_sync.sh
+++ b/scripts/manual/run_upstream_av_sync.sh
@@ -887,6 +887,7 @@ lines = [
     f"- video onsets: {report['video_event_count']}",
     f"- audio onsets: {report['audio_event_count']}",
     f"- paired pulses: {report['paired_event_count']}",
+    f"- activity start delta: {report.get('activity_start_delta_ms', 0.0):+.1f} ms (audio after video is positive)",
     f"- first skew: {report['first_skew_ms']:+.1f} ms (audio after video is positive)",
     f"- last skew: {report['last_skew_ms']:+.1f} ms",
     f"- mean skew: {report['mean_skew_ms']:+.1f} ms",
diff --git a/scripts/manual/run_upstream_browser_av_sync.sh b/scripts/manual/run_upstream_browser_av_sync.sh
index 7dcb5ee..24d232d 100755
--- a/scripts/manual/run_upstream_browser_av_sync.sh
+++ b/scripts/manual/run_upstream_browser_av_sync.sh
@@ -29,6 +29,7 @@ READY_TIMEOUT_SECONDS=${READY_TIMEOUT_SECONDS:-120}
 mkdir -p "${LOCAL_OUTPUT_DIR}"
 STAMP="$(date +%Y%m%d-%H%M%S)"
 LOCAL_CAPTURE="${LOCAL_OUTPUT_DIR}/lesavka-browser-av-sync-${STAMP}.webm"
+LOCAL_REPORT_DIR="${LOCAL_OUTPUT_DIR}/lesavka-browser-av-sync-${STAMP}"
 
 scp ${SSH_OPTS} "${REPO_ROOT}/scripts/manual/browser_consumer_probe.py" "${TETHYS_HOST}:${REMOTE_SCRIPT}"
 
@@ -162,8 +163,11 @@ scp ${SSH_OPTS} "${TETHYS_HOST}:${REMOTE_CAPTURE}" "${LOCAL_CAPTURE}"
 echo "==> analyzing browser capture"
 (
   cd "${REPO_ROOT}"
-  cargo run -p lesavka_client --bin lesavka-sync-analyze -- "${LOCAL_CAPTURE}"
+  cargo run -p lesavka_client --bin lesavka-sync-analyze -- \
+    --report-dir "${LOCAL_REPORT_DIR}" \
+    "${LOCAL_CAPTURE}"
 )
 
 echo "==> done"
 echo "capture: ${LOCAL_CAPTURE}"
+echo "report_dir: ${LOCAL_REPORT_DIR}"
diff --git a/server/Cargo.toml b/server/Cargo.toml
index 939064c..5a8e580 100644
--- a/server/Cargo.toml
+++ b/server/Cargo.toml
@@ -10,7 +10,7 @@ bench                   = false
 
 [package]
 name                    = "lesavka_server"
-version                 = "0.16.11"
+version                 = "0.16.12"
 edition                 = "2024"
 autobins                = false