diff --git a/internal/telemetry/launch_source.go b/internal/telemetry/launch_source.go
index f71bfbb0..3459daa9 100644
--- a/internal/telemetry/launch_source.go
+++ b/internal/telemetry/launch_source.go
@@ -1,5 +1,7 @@
 package telemetry
 
+import "sync"
+
 // LaunchSource identifies how the current mcpproxy process was launched, for
 // retention telemetry (spec 044). Detection happens once at process startup
 // (via DetectLaunchSourceOnce, added in a later task), with a one-shot
@@ -110,11 +112,17 @@ var (
 )
 
 // launchSourceOnceT is a test-friendly sync.Once clone with reset support.
+// Do is mutex-guarded: DetectLaunchSourceOnce is reached concurrently by every
+// telemetry-reporting surface (two listeners' status handlers race here), and
+// the mutex also orders the launchSourceCached write before any post-Do read.
 type launchSourceOnceT struct {
+	mu   sync.Mutex
 	done bool
 }
 
 func (o *launchSourceOnceT) Do(f func()) {
+	o.mu.Lock()
+	defer o.mu.Unlock()
 	if o.done {
 		return
 	}
@@ -124,7 +132,9 @@ func (o *launchSourceOnceT) Do(f func()) {
 
 // resetLaunchSourceOnce is exposed for tests (lower-case).
 func resetLaunchSourceOnce() {
-	launchSourceOnce = launchSourceOnceT{}
+	launchSourceOnce.mu.Lock()
+	defer launchSourceOnce.mu.Unlock()
+	launchSourceOnce.done = false
 	launchSourceCached = ""
 }
 
diff --git a/internal/telemetry/launch_source_test.go b/internal/telemetry/launch_source_test.go
index 34016820..ecfc2455 100644
--- a/internal/telemetry/launch_source_test.go
+++ b/internal/telemetry/launch_source_test.go
@@ -1,6 +1,7 @@
 package telemetry
 
 import (
+	"sync"
 	"testing"
 )
 
@@ -166,3 +167,30 @@ func TestDetectLaunchSourceOnce_Cached(t *testing.T) {
 		t.Fatalf("DetectLaunchSourceOnce returned invalid %q", first)
 	}
 }
+
+// DetectLaunchSourceOnce is reached concurrently by every surface that reports
+// telemetry (two listeners' /api/v1/status handlers race here in practice);
+// the once-guard must be goroutine-safe. Red under -race before the guard
+// gained its mutex.
+func TestDetectLaunchSourceOnceConcurrent(t *testing.T) {
+	resetLaunchSourceOnce()
+	t.Cleanup(resetLaunchSourceOnce)
+
+	const goroutines = 32
+	results := make([]LaunchSource, goroutines)
+	var wg sync.WaitGroup
+	wg.Add(goroutines)
+	for i := 0; i < goroutines; i++ {
+		go func(i int) {
+			defer wg.Done()
+			results[i] = DetectLaunchSourceOnce()
+		}(i)
+	}
+	wg.Wait()
+
+	for i := 1; i < goroutines; i++ {
+		if results[i] != results[0] {
+			t.Fatalf("goroutine %d saw %q, goroutine 0 saw %q", i, results[i], results[0])
+		}
+	}
+}