diff --git a/CHANGELOG.md b/CHANGELOG.md
index 05350ed..d6921b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -62,6 +62,22 @@ with v0.2.x peers.
 - TLV extension section added to LookupRequest and LookupResponse
   after fixed fields. Transit nodes forward TLV bytes verbatim.
 
+#### Nostr-Discovery Advert Namespace
+
+- Default Nostr-discovery advert namespace bumped from
+  `fips-overlay-v1` to `fips-overlay-v1-next` on the `next` branch.
+  Master continues to publish under `fips-overlay-v1`. Effect: a
+  stock `next`-branch daemon's open-discovery sweep no longer
+  discovers `master` peers, and vice versa — eliminating the
+  cross-version retraversal storms that arise when both sides
+  punched a UDP socket via Nostr but cannot complete an FMP
+  handshake. Operators who genuinely want cross-branch reach (e.g.
+  during a coordinated rolling upgrade) can override per-daemon
+  via `node.discovery.nostr.app` in `fips.yaml`. The
+  `protocol_mismatch_cooldown_secs` defense-in-depth on master is
+  the safety net against any peer that bypasses this default
+  (config override, future fork, static-peer config).
+
 #### Shared-Media Beacons
 
 - Ethernet frame header unified to 4 bytes `[type][flags][length:2
diff --git a/src/config/node.rs b/src/config/node.rs
index 5add977..7d5515e 100644
--- a/src/config/node.rs
+++ b/src/config/node.rs
@@ -462,7 +462,11 @@ impl NostrDiscoveryConfig {
     }
 
     fn default_app() -> String {
-        "fips-overlay-v1".to_string()
+        // Branch-specific default. `next` runs FMP-v1 which is wire-
+        // incompatible with `master`'s FMP-v0, so the two namespaces
+        // separate the discovery overlays by default — operators who
+        // want cross-branch discovery can override here.
+        "fips-overlay-v1-next".to_string()
     }
 
     fn default_signal_ttl_secs() -> u64 {
diff --git a/src/discovery/nostr/tests.rs b/src/discovery/nostr/tests.rs
index b412058..03bc236 100644
--- a/src/discovery/nostr/tests.rs
+++ b/src/discovery/nostr/tests.rs
@@ -39,7 +39,7 @@ fn can_reach(local_nat: NatType, remote_nat: NatType) -> bool {
 
 fn signed_overlay_advert_event(created_at_secs: u64, expiration_secs: Option<u64>) -> nostr::Event {
     let keys = nostr::Keys::generate();
-    let content = r#"{"identifier":"fips-overlay-v1","version":1,"endpoints":[{"transport":"tcp","addr":"203.0.113.10:443"}]}"#;
+    let content = r#"{"identifier":"fips-overlay-v1-next","version":1,"endpoints":[{"transport":"tcp","addr":"203.0.113.10:443"}]}"#;
     let mut builder = EventBuilder::new(Kind::Custom(ADVERT_KIND), content)
         .custom_created_at(Timestamp::from(created_at_secs));
     if let Some(expiration_secs) = expiration_secs {
diff --git a/src/discovery/nostr/types.rs b/src/discovery/nostr/types.rs
index 3d76419..c0d5f73 100644
--- a/src/discovery/nostr/types.rs
+++ b/src/discovery/nostr/types.rs
@@ -3,7 +3,14 @@ use crate::discovery::EstablishedTraversal;
 use serde::{Deserialize, Serialize};
 
 pub const ADVERT_KIND: u16 = 37195;
-pub const ADVERT_IDENTIFIER: &str = "fips-overlay-v1";
+/// Default Nostr-discovery advert namespace identifier on the `next`
+/// branch. Distinct from `master`'s `fips-overlay-v1` so peers running
+/// the FMP-v1 protocol on `next` are not discovered by `master` peers
+/// (and vice versa) — the `next`-branch FMP wire format is incompatible
+/// with `master`'s, so cross-branch discovery only ever produces failed
+/// handshakes. Operators who genuinely want cross-branch reach can
+/// override per-peer via `node.discovery.nostr.app` in config.
+pub const ADVERT_IDENTIFIER: &str = "fips-overlay-v1-next";
 pub const ADVERT_VERSION: u32 = 1;
 pub const SIGNAL_KIND: u16 = 21059;
 // Defined at the top-level `discovery` module; re-exported here so the
diff --git a/testing/nat/scripts/nostr-relay-test.sh b/testing/nat/scripts/nostr-relay-test.sh
index 4057e9f..e00e673 100755
--- a/testing/nat/scripts/nostr-relay-test.sh
+++ b/testing/nat/scripts/nostr-relay-test.sh
@@ -191,7 +191,7 @@ pubkey = xonly_pubkey(secret).hex()
 created_at = int(time.time())
 kind = 37195
 tags = [
-    ["d", "fips-overlay-v1"],
+    ["d", "fips-overlay-v1-next"],
     ["app", "fips.nat.lab.v1"],
 ]
 content = "this-is-not-a-valid-overlay-advert-{garbage}"