diff --git a/AGENTS.md b/AGENTS.md
index fa254eb..6b74f0d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -393,3 +393,19 @@ evidence.
 - [x] Run shell syntax checks, focused contract tests, and package checks.
 - [x] Push clean semver `0.17.18` for installed client/server testing.
 - [ ] Re-run the mirrored probe only after confirming the intended microphone is physically present and selected.
+
+## 0.17.19 Fatal Required Source Failure Checklist
+
+Context: the 0.17.18 run proved fallback was blocked, but the headless client kept running
+camera-only after the required Bumblebee source failed to open. The server stayed in `acquiring`
+for all four segments (`awaiting both upstream media streams`), the analyzer saw no color-coded
+video pulses, and no calibration data was produced. Required-source failure must fail the probe,
+not degrade into camera-only evidence.
+
+- [x] Treat the 0.17.18 run as a required-microphone setup failure, not a lip-sync measurement.
+- [x] Keep strict no-fallback behavior from 0.17.18.
+- [x] Abort the client process when an explicit required microphone source cannot start.
+- [x] Abort the client process when an explicit required camera source cannot start.
+- [x] Run shell syntax checks, focused contract tests, and package checks.
+- [x] Push clean semver `0.17.19` for installed client/server testing.
+- [ ] Re-run only after `LESAVKA_MIC_SOURCE` is listed by the local audio stack.
diff --git a/Cargo.lock b/Cargo.lock
index 806e0a9..1b6a39c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1652,7 +1652,7 @@ checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
 [[package]]
 name = "lesavka_client"
-version = "0.17.18"
+version = "0.17.19"
 dependencies = [
  "anyhow",
  "async-stream",
@@ -1686,7 +1686,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_common"
-version = "0.17.18"
+version = "0.17.19"
 dependencies = [
  "anyhow",
  "base64",
@@ -1698,7 +1698,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_server"
-version = "0.17.18"
+version = "0.17.19"
 dependencies = [
  "anyhow",
  "base64",
diff --git a/client/Cargo.toml b/client/Cargo.toml
index 3c793df..ec76e19 100644
--- a/client/Cargo.toml
+++ b/client/Cargo.toml
@@ -4,7 +4,7 @@ path                    = "src/main.rs"
 
 [package]
 name                    = "lesavka_client"
-version                 = "0.17.18"
+version                 = "0.17.19"
 edition                 = "2024"
 
 [dependencies]
diff --git a/client/src/app/uplink_media.rs b/client/src/app/uplink_media.rs
index 945ac28..60d5d2b 100644
--- a/client/src/app/uplink_media.rs
+++ b/client/src/app/uplink_media.rs
@@ -40,6 +40,7 @@ impl LesavkaClientApp {
                         "🎤 microphone uplink setup failed for {:?}: {err:#}",
                         active_source.as_deref().unwrap_or("auto")
                     );
+                    abort_if_required_media_source_failed("microphone", "🎤", active_source.as_deref(), &err);
                     delay = app_support::next_delay(delay);
                     tokio::time::sleep(delay).await;
                     continue;
@@ -47,6 +48,12 @@ impl LesavkaClientApp {
                 Err(err) => {
                     telemetry.record_disconnect(format!("microphone uplink setup task failed: {err}"));
                     warn!("🎤 microphone uplink setup task failed before StreamMicrophone could start: {err}");
+                    abort_if_required_media_source_failed(
+                        "microphone",
+                        "🎤",
+                        active_source.as_deref(),
+                        &err,
+                    );
                     delay = app_support::next_delay(delay);
                     tokio::time::sleep(delay).await;
                     continue;
@@ -216,6 +223,7 @@ impl LesavkaClientApp {
                         "📸 webcam uplink setup failed for {:?}: {err:#}",
                         active_source.as_deref().unwrap_or("auto")
                     );
+                    abort_if_required_media_source_failed("camera", "📸", active_source.as_deref(), &err);
                     delay = app_support::next_delay(delay);
                     tokio::time::sleep(delay).await;
                     continue;
@@ -223,6 +231,12 @@ impl LesavkaClientApp {
                 Err(err) => {
                     telemetry.record_disconnect(format!("webcam uplink setup task failed: {err}"));
                     warn!("📸 webcam uplink setup task failed before StreamCamera could start: {err}");
+                    abort_if_required_media_source_failed(
+                        "camera",
+                        "📸",
+                        active_source.as_deref(),
+                        &err,
+                    );
                     delay = app_support::next_delay(delay);
                     tokio::time::sleep(delay).await;
                     continue;
@@ -412,6 +426,39 @@ fn parse_camera_profile_id(raw: &str) -> Option<(u32, u32, u32)> {
     (width > 0 && height > 0 && fps > 0).then_some((width, height, fps))
 }
 
+#[cfg(not(coverage))]
+fn abort_if_required_media_source_failed(
+    kind: &str,
+    icon: &str,
+    source: Option<&str>,
+    err: &dyn std::fmt::Display,
+) {
+    if !explicit_media_sources_required() || source.is_none_or(|source| source.trim().is_empty()) {
+        return;
+    }
+    let source = source.expect("checked source presence");
+    error!(
+        "{icon} required {kind} source '{source}' failed to start; aborting client because LESAVKA_REQUIRE_EXPLICIT_MEDIA_SOURCES=1: {err}"
+    );
+    eprintln!(
+        "{icon} required {kind} source '{source}' failed to start; aborting client because LESAVKA_REQUIRE_EXPLICIT_MEDIA_SOURCES=1: {err}"
+    );
+    std::process::exit(2);
+}
+
+#[cfg(not(coverage))]
+fn explicit_media_sources_required() -> bool {
+    std::env::var("LESAVKA_REQUIRE_EXPLICIT_MEDIA_SOURCES")
+        .ok()
+        .is_some_and(|value| {
+            let value = value.trim();
+            value == "1"
+                || value.eq_ignore_ascii_case("true")
+                || value.eq_ignore_ascii_case("yes")
+                || value.eq_ignore_ascii_case("on")
+        })
+}
+
 #[cfg(not(coverage))]
 const VIDEO_UPLINK_QUEUE: crate::uplink_fresh_queue::FreshQueueConfig =
     crate::uplink_fresh_queue::FreshQueueConfig {
diff --git a/common/Cargo.toml b/common/Cargo.toml
index 6ad1733..bb188a0 100644
--- a/common/Cargo.toml
+++ b/common/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name                    = "lesavka_common"
-version                 = "0.17.18"
+version                 = "0.17.19"
 edition                 = "2024"
 build                   = "build.rs"
 
diff --git a/server/Cargo.toml b/server/Cargo.toml
index 599ed57..6c2ceea 100644
--- a/server/Cargo.toml
+++ b/server/Cargo.toml
@@ -10,7 +10,7 @@ bench                   = false
 
 [package]
 name                    = "lesavka_server"
-version                 = "0.17.18"
+version                 = "0.17.19"
 edition                 = "2024"
 autobins                = false
 
diff --git a/testing/tests/client_uplink_freshness_contract.rs b/testing/tests/client_uplink_freshness_contract.rs
index f12bdc6..eb6bd6f 100644
--- a/testing/tests/client_uplink_freshness_contract.rs
+++ b/testing/tests/client_uplink_freshness_contract.rs
@@ -121,3 +121,20 @@ fn sync_probe_audio_queue_preserves_bounded_marker_continuity() {
     );
     assert_queue_policy(block, "PROBE_AUDIO_QUEUE", "DrainOldest");
 }
+
+#[test]
+fn strict_explicit_media_source_failures_abort_the_headless_probe_client() {
+    for expected in [
+        "LESAVKA_REQUIRE_EXPLICIT_MEDIA_SOURCES",
+        "abort_if_required_media_source_failed",
+        "required {kind} source '{source}' failed to start",
+        "std::process::exit(2)",
+        "abort_if_required_media_source_failed(\"microphone\"",
+        "abort_if_required_media_source_failed(\"camera\"",
+    ] {
+        assert!(
+            UPLINK_MEDIA_SRC.contains(expected),
+            "required-source setup failures must be fatal in strict probe mode: missing {expected}"
+        );
+    }
+}