diff --git a/quic/interop/build.gradle.kts b/quic/interop/build.gradle.kts
index edd1ee3b3..09cae4e32 100644
--- a/quic/interop/build.gradle.kts
+++ b/quic/interop/build.gradle.kts
@@ -44,6 +44,7 @@ sourceSets {
 dependencies {
     implementation(project(":quic"))
     implementation(libs.kotlinx.coroutines.core)
+    implementation(libs.jackson.module.kotlin)
 
     testImplementation(libs.kotlin.test)
 }
diff --git a/quic/interop/run-matrix.sh b/quic/interop/run-matrix.sh
index 10a23e2c3..dbfa4f1a5 100755
--- a/quic/interop/run-matrix.sh
+++ b/quic/interop/run-matrix.sh
@@ -112,6 +112,15 @@ fi
 # per-invocation subdirectory under $LOG_DIR. The parent must exist; the
 # child must not. Tail of `ls -t "$LOG_DIR" | head -1` finds the latest.
 #
+# NOTE: this script is NOT safe to run concurrently against itself.
+# quic-interop-runner's docker-compose.yml hardcodes `container_name:
+# sim/server/client`, which Docker enforces globally regardless of
+# COMPOSE_PROJECT_NAME. Two simultaneous invocations collide on
+# `docker create container "sim"`. Run sequentially:
+#   for peer in aioquic picoquic quic-go; do
+#       quic/interop/run-matrix.sh -s $peer -t handshake,chacha20,...
+#   done
+#
 # Output filter: by default we drop the runner / container boilerplate
 # (interface checksum offload toggles, route setup, container lifecycle,
 # the long Command: WAITFORSERVER=... line, the platform-mismatch warning
diff --git a/quic/interop/src/main/kotlin/com/vitorpamplona/quic/interop/runner/InteropClient.kt b/quic/interop/src/main/kotlin/com/vitorpamplona/quic/interop/runner/InteropClient.kt
index 111b7dc93..7f3fd956c 100644
--- a/quic/interop/src/main/kotlin/com/vitorpamplona/quic/interop/runner/InteropClient.kt
+++ b/quic/interop/src/main/kotlin/com/vitorpamplona/quic/interop/runner/InteropClient.kt
@@ -141,7 +141,12 @@ fun main() {
             "handshake", "chacha20", "handshakeloss",
             "transfer", "http3", "multiplexing",
             "transferloss", "transfercorruption", "longrtt", "goodput", "crosstraffic",
-            "retry", "ipv6", "versionnegotiation",
+            "retry", "ipv6",
+            // NOTE: the runner does NOT have a `versionnegotiation` testcase
+            // (its Available list excludes it). The :quic VN-handling code
+            // (applyVersionNegotiation, FORCE_VERSION_NEGOTIATION constant)
+            // stays as defensive support for any server that decides to
+            // send a VN packet at us, but no testcase exercises it directly.
             -> {
                 runTransferTest(
                     requests = requests,