diff --git a/tools/marmot-interop/headless/patches/whitenoise-skip-unprocessable-retry.patch b/tools/marmot-interop/headless/patches/whitenoise-skip-unprocessable-retry.patch
new file mode 100644
index 000000000..3d2745db9
--- /dev/null
+++ b/tools/marmot-interop/headless/patches/whitenoise-skip-unprocessable-retry.patch
@@ -0,0 +1,27 @@
+--- a/src/whitenoise/event_processor/account_event_processor.rs
++++ b/src/whitenoise/event_processor/account_event_processor.rs
+@@ -178,7 +178,23 @@
+             }
+             Err(e) => {
+                 // Handle retry logic for actual processing errors
+-                if retry_info.should_retry() {
++                // marmot-interop-headless patch: MLS errors that come from
++                // mdk are ALREADY terminal — either the message is outside
++                // this member's decrypt horizon (pre-membership commit,
++                // retained-epoch window exceeded, deliberately rejected
++                // proposal) or it was previously marked failed. Retrying
++                // them 10 times with exponential backoff (total ~17 min)
++                // just blocks later decryptable commits behind a queue of
++                // doomed retries, so every later join / rename / leave
++                // propagation races the test timeout. Treat them all as
++                // one-shot: log once, move on.
++                let is_terminal = matches!(
++                    e,
++                    WhitenoiseError::MlsMessageUnprocessable(_)
++                        | WhitenoiseError::MlsMessagePreviouslyFailed
++                        | WhitenoiseError::MdkCoreError(_),
++                );
++                if !is_terminal && retry_info.should_retry() {
+                     self.schedule_retry(event, source, retry_info, e);
+                 } else {
+                     tracing::error!(
diff --git a/tools/marmot-interop/headless/setup.sh b/tools/marmot-interop/headless/setup.sh
index 797c0116b..c58658a65 100644
--- a/tools/marmot-interop/headless/setup.sh
+++ b/tools/marmot-interop/headless/setup.sh
@@ -39,7 +39,7 @@ preflight() {
       2>&1 | tee -a "$LOG_FILE"
   fi
 
-  # Three harness-only patches to wnd so it runs fully offline / in
+  # Four harness-only patches to wnd so it runs fully offline / in
   # sandboxes that block outbound + kernel keyring:
   #   1. discovery-env: honour $WHITENOISE_DISCOVERY_RELAYS so we can
   #      point wnd at our loopback relay instead of the baked-in public
@@ -54,10 +54,18 @@ preflight() {
   #      primal.net / nos.lol, and every later activate / publish burns
   #      connection budget on unreachable sockets — enough to break the
   #      account-inbox subscription plane and drop kind:1059 delivery.
+  #   4. skip-unprocessable-retry: when mdk-core returns
+  #      `MlsMessageUnprocessable` (pre-membership commit, too-old epoch)
+  #      the message is provably undecryptable — retrying it ten times
+  #      with exponential backoff (total ~17 min) just blocks later
+  #      decryptable commits behind a queue of doomed retries, which in
+  #      the harness manifests as "A already left" / "name unchanged"
+  #      timeouts. The patch treats that error as terminal.
   local -a patches=(
     "whitenoise-discovery-env.patch"
     "whitenoise-mock-keyring.patch"
     "whitenoise-defaults-env.patch"
+    "whitenoise-skip-unprocessable-retry.patch"
   )
   for name in "${patches[@]}"; do
     local marker="$WN_REPO/.headless-patched-${name%.patch}"