--- a/src/relay_control/discovery.rs
+++ b/src/relay_control/discovery.rs
@@ -87,6 +87,20 @@

     /// Initial curated relay set from the planning doc.
     pub(crate) fn curated_default_relays() -> Vec<RelayUrl> {
+        // marmot-interop-headless patch: honour $WHITENOISE_DISCOVERY_RELAYS
+        // (comma-separated list) when present, so the harness can force wnd
+        // to use a loopback relay instead of the baked-in public set.
+        if let Ok(from_env) = std::env::var("WHITENOISE_DISCOVERY_RELAYS") {
+            let parsed: Vec<RelayUrl> = from_env
+                .split(',')
+                .map(str::trim)
+                .filter(|s| !s.is_empty())
+                .filter_map(|u| RelayUrl::parse(u).ok())
+                .collect();
+            if !parsed.is_empty() {
+                return parsed;
+            }
+        }
         [
             "wss://index.hzrd149.com",
             "wss://indexer.coracle.social",