- inspect the event name in the debug log so client-controlled newlines
  or escape sequences cannot forge log content
- restore payload_type to the rejection telemetry, using inspect_type/1
  (unused since 62630e5e, which failed compile --warnings-as-errors)

@@ -239,0 +242,4 @@
+  # payload itself is never logged or mirrored into telemetry — only its
+  # rough shape — so a hostile frame cannot inject log content.
+  def handle_in(event, payload, socket) do
+    emit_payload_rejected("unmatched_event", %{event: event, payload_type: inspect_type(payload)})

@@ -239,0 +241,4 @@
+  # crashing the channel (and minting an ErrorTracker row per frame). The
+  # payload itself is never logged or mirrored into telemetry — only its
+  # rough shape — so a hostile frame cannot inject log content.
+  def handle_in(event, payload, socket) do

@@ -239,0 +245,4 @@
+    # Telemetry stays (cheap, aggregated); the log drops to debug because this
+    # clause sits behind no rate limit — one socket can push unknown events at
+    # line rate, and a warning per frame hands log volume to the client.
+    Logger.debug("Mobile channel unmatched event: #{event}")