diff --git a/crates/wzp-android/src/engine.rs b/crates/wzp-android/src/engine.rs
index 476ed82..751d976 100644
--- a/crates/wzp-android/src/engine.rs
+++ b/crates/wzp-android/src/engine.rs
@@ -23,7 +23,7 @@ use wzp_fec::{RaptorQFecDecoder, RaptorQFecEncoder};
 use wzp_proto::{
     AdaptiveQualityController, AudioDecoder, AudioEncoder, CodecId, FecDecoder, FecEncoder,
     MediaHeader, MediaPacket, MediaTransport, MediaType, QualityController, QualityProfile,
-    SignalMessage,
+    SignalMessage, default_signal_version,
 };
 
 use crate::audio_ring::AudioRing;
@@ -321,11 +321,12 @@ impl WzpEngine {
 
             // Auth if token provided
             if let Some(ref tok) = token {
-                let _ = transport.send_signal(&SignalMessage::AuthToken { token: tok.clone() }).await;
+                let _ = transport.send_signal(&SignalMessage::AuthToken { version: default_signal_version(),  token: tok.clone() }).await;
             }
 
             // Register presence
             let _ = transport.send_signal(&SignalMessage::RegisterPresence {
+                version: default_signal_version(),
                 identity_pub,
                 signature: vec![],
                 alias: alias.clone(),
@@ -350,7 +351,7 @@ impl WzpEngine {
                     break;
                 }
                 match transport.recv_signal().await {
-                    Ok(Some(SignalMessage::CallRinging { call_id })) => {
+                    Ok(Some(SignalMessage::CallRinging { call_id, ..})) => {
                         info!(call_id = %call_id, "signal: ringing");
                         let mut stats = signal_state.stats.lock().unwrap();
                         stats.state = crate::stats::CallState::Ringing;
@@ -522,6 +523,7 @@ async fn run_call(
     let signature = kx.sign(&sign_data);
 
     let offer = SignalMessage::CallOffer {
+        version: default_signal_version(),
         identity_pub,
         ephemeral_pub,
         signature,
@@ -1223,6 +1225,7 @@ async fn run_call(
                 Ok(Some(SignalMessage::RoomUpdate {
                     count,
                     participants,
+                    ..
                 })) => {
                     info!(count, "RoomUpdate received");
                     let members: Vec<crate::stats::RoomMember> = participants
@@ -1240,6 +1243,7 @@ async fn run_call(
                 Ok(Some(SignalMessage::QualityDirective {
                     recommended_profile,
                     reason,
+                    ..
                 })) => {
                     let idx = profile_to_index(&recommended_profile);
                     info!(
diff --git a/crates/wzp-client/src/analyzer.rs b/crates/wzp-client/src/analyzer.rs
index 54553ac..3f06319 100644
--- a/crates/wzp-client/src/analyzer.rs
+++ b/crates/wzp-client/src/analyzer.rs
@@ -15,7 +15,7 @@ use std::time::{Duration, Instant};
 use clap::Parser;
 use tracing::info;
 
-use wzp_proto::{CodecId, MediaPacket, MediaTransport};
+use wzp_proto::{CodecId, MediaPacket, MediaTransport, default_signal_version};
 
 // ---------------------------------------------------------------------------
 // CLI
@@ -919,6 +919,7 @@ async fn main() -> anyhow::Result<()> {
     // Auth if token provided
     if let Some(ref token) = args.token {
         let auth = wzp_proto::SignalMessage::AuthToken {
+            version: default_signal_version(),
             token: token.clone(),
         };
         transport.send_signal(&auth).await?;
diff --git a/crates/wzp-client/src/cli.rs b/crates/wzp-client/src/cli.rs
index 43a8d7a..573605b 100644
--- a/crates/wzp-client/src/cli.rs
+++ b/crates/wzp-client/src/cli.rs
@@ -17,7 +17,7 @@ use std::sync::Arc;
 use tracing::{error, info};
 
 use wzp_client::call::{CallConfig, CallDecoder, CallEncoder};
-use wzp_proto::MediaTransport;
+use wzp_proto::{MediaTransport, default_signal_version};
 
 const FRAME_SAMPLES: usize = 960; // 20ms @ 48kHz
 
@@ -380,6 +380,7 @@ async fn main() -> anyhow::Result<()> {
     // Send auth token if provided (relay with --auth-url expects this first)
     if let Some(ref token) = cli.token {
         let auth = wzp_proto::SignalMessage::AuthToken {
+            version: default_signal_version(),
             token: token.clone(),
         };
         transport.send_signal(&auth).await?;
@@ -473,6 +474,7 @@ async fn run_silence(transport: Arc<wzp_transport::QuinnTransport>) -> anyhow::R
 
     info!(total_source, total_repair, total_bytes, "done — closing");
     let hangup = wzp_proto::SignalMessage::Hangup {
+        version: default_signal_version(),
         reason: wzp_proto::HangupReason::Normal,
         call_id: None,
     };
@@ -632,6 +634,7 @@ async fn run_file_mode(
 
     // Send Hangup signal so the relay knows we're done
     let hangup = wzp_proto::SignalMessage::Hangup {
+        version: default_signal_version(),
         reason: wzp_proto::HangupReason::Normal,
         call_id: None,
     };
@@ -769,7 +772,7 @@ async fn run_signal_mode(
     token: Option<String>,
     call_target: Option<String>,
 ) -> anyhow::Result<()> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
 
     let identity = seed.derive_identity();
     let pub_id = identity.public_identity();
@@ -792,13 +795,17 @@ async fn run_signal_mode(
     // Auth if token provided
     if let Some(ref tok) = token {
         transport
-            .send_signal(&SignalMessage::AuthToken { token: tok.clone() })
+            .send_signal(&SignalMessage::AuthToken {
+                version: default_signal_version(),
+                token: tok.clone(),
+            })
             .await?;
     }
 
     // Register presence (signature not verified in Phase 1)
     transport
         .send_signal(&SignalMessage::RegisterPresence {
+            version: default_signal_version(),
             identity_pub,
             signature: vec![], // Phase 1: not verified
             alias: None,
@@ -835,6 +842,7 @@ async fn run_signal_mode(
 
         transport
             .send_signal(&SignalMessage::DirectCallOffer {
+                version: default_signal_version(),
                 caller_fingerprint: fp.clone(),
                 caller_alias: None,
                 target_fingerprint: target.clone(),
@@ -861,7 +869,7 @@ async fn run_signal_mode(
     loop {
         match signal_transport.recv_signal().await {
             Ok(Some(msg)) => match msg {
-                SignalMessage::CallRinging { call_id } => {
+                SignalMessage::CallRinging { call_id, .. } => {
                     info!(call_id = %call_id, "ringing...");
                 }
                 SignalMessage::DirectCallOffer {
@@ -879,6 +887,7 @@ async fn run_signal_mode(
                     // Auto-accept for CLI testing
                     let _ = signal_transport
                         .send_signal(&SignalMessage::DirectCallAnswer {
+                            version: default_signal_version(),
                             call_id,
                             accept_mode: wzp_proto::CallAcceptMode::AcceptGeneric,
                             identity_pub: Some(identity_pub),
@@ -908,6 +917,7 @@ async fn run_signal_mode(
                     peer_direct_addr: _,
                     peer_local_addrs: _,
                     peer_mapped_addr: _,
+                    ..
                 } => {
                     info!(call_id = %call_id, room = %room, relay = %setup_relay, "call setup — connecting to media room");
 
@@ -970,6 +980,7 @@ async fn run_signal_mode(
                                             _ = tokio::signal::ctrl_c() => {
                                                 info!("hanging up...");
                                                 let _ = signal_transport.send_signal(&SignalMessage::Hangup {
+                                                    version: default_signal_version(),
                                                     reason: wzp_proto::HangupReason::Normal,
                                                     call_id: None,
                                                 }).await;
diff --git a/crates/wzp-client/src/featherchat.rs b/crates/wzp-client/src/featherchat.rs
index 3be0b55..f6bb4c7 100644
--- a/crates/wzp-client/src/featherchat.rs
+++ b/crates/wzp-client/src/featherchat.rs
@@ -11,7 +11,7 @@
 //! 5. Connects QUIC to relay for media
 
 use serde::{Deserialize, Serialize};
-use wzp_proto::packet::SignalMessage;
+use wzp_proto::packet::{SignalMessage, default_signal_version};
 
 /// featherChat CallSignal types (mirrors warzone-protocol::message::CallSignalType).
 #[derive(Clone, Debug, Serialize, Deserialize)]
@@ -152,6 +152,7 @@ mod tests {
     #[test]
     fn payload_roundtrip() {
         let signal = SignalMessage::CallOffer {
+            version: default_signal_version(),
             identity_pub: [1u8; 32],
             ephemeral_pub: [2u8; 32],
             signature: vec![3u8; 64],
@@ -172,6 +173,7 @@ mod tests {
     #[test]
     fn signal_type_mapping() {
         let offer = SignalMessage::CallOffer {
+            version: default_signal_version(),
             identity_pub: [0; 32],
             ephemeral_pub: [0; 32],
             signature: vec![],
@@ -183,6 +185,7 @@ mod tests {
         assert!(matches!(signal_to_call_type(&offer), CallSignalType::Offer));
 
         let hangup = SignalMessage::Hangup {
+            version: default_signal_version(),
             reason: wzp_proto::HangupReason::Normal,
             call_id: None,
         };
@@ -209,6 +212,7 @@ mod tests {
         ));
 
         let transfer = SignalMessage::Transfer {
+            version: default_signal_version(),
             target_fingerprint: "abc".to_string(),
             relay_addr: None,
         };
diff --git a/crates/wzp-client/src/handshake.rs b/crates/wzp-client/src/handshake.rs
index 8e5ec63..dd14419 100644
--- a/crates/wzp-client/src/handshake.rs
+++ b/crates/wzp-client/src/handshake.rs
@@ -4,7 +4,9 @@
 //! send `CallOffer` → recv `CallAnswer` → derive shared `CryptoSession`.
 
 use wzp_crypto::{CryptoSession, KeyExchange, WarzoneKeyExchange};
-use wzp_proto::{HangupReason, MediaTransport, QualityProfile, SignalMessage};
+use wzp_proto::{
+    HangupReason, MediaTransport, QualityProfile, SignalMessage, default_signal_version,
+};
 
 /// Errors that can occur during the client-side cryptographic handshake.
 #[derive(Debug)]
@@ -78,6 +80,7 @@ pub async fn perform_handshake(
 
     // 4. Send CallOffer
     let offer = SignalMessage::CallOffer {
+        version: default_signal_version(),
         identity_pub,
         ephemeral_pub,
         signature,
@@ -112,6 +115,7 @@ pub async fn perform_handshake(
                 ephemeral_pub,
                 signature,
                 chosen_profile,
+                ..
             } => (identity_pub, ephemeral_pub, signature, chosen_profile),
             SignalMessage::Hangup {
                 reason: HangupReason::ProtocolVersionMismatch { server_supported },
diff --git a/crates/wzp-client/src/ice_agent.rs b/crates/wzp-client/src/ice_agent.rs
index 10ca001..9b1e6ef 100644
--- a/crates/wzp-client/src/ice_agent.rs
+++ b/crates/wzp-client/src/ice_agent.rs
@@ -17,7 +17,7 @@ use std::net::SocketAddr;
 use std::sync::atomic::{AtomicU32, Ordering};
 use std::time::Duration;
 
-use wzp_proto::SignalMessage;
+use wzp_proto::{SignalMessage, default_signal_version};
 
 use crate::dual_path::PeerCandidates;
 use crate::portmap;
@@ -133,6 +133,7 @@ impl IceAgent {
         let candidates = self.gather().await;
 
         let update = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: self.call_id.clone(),
             reflexive_addr: candidates.reflexive.map(|a| a.to_string()),
             local_addrs: candidates.local.iter().map(|a| a.to_string()).collect(),
@@ -206,6 +207,7 @@ mod tests {
 
         // First update (gen=1) should succeed.
         let update1 = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-call".into(),
             reflexive_addr: Some("203.0.113.5:4433".into()),
             local_addrs: vec!["192.168.1.10:4433".into()],
@@ -223,6 +225,7 @@ mod tests {
 
         // Same generation (gen=1) should be rejected.
         let update1b = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-call".into(),
             reflexive_addr: Some("198.51.100.9:4433".into()),
             local_addrs: vec![],
@@ -233,6 +236,7 @@ mod tests {
 
         // Older generation (gen=0) should be rejected.
         let update0 = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-call".into(),
             reflexive_addr: Some("10.0.0.1:4433".into()),
             local_addrs: vec![],
@@ -243,6 +247,7 @@ mod tests {
 
         // Newer generation (gen=2) should succeed.
         let update2 = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-call".into(),
             reflexive_addr: Some("198.51.100.9:5555".into()),
             local_addrs: vec![],
@@ -287,6 +292,7 @@ mod tests {
         let agent = IceAgent::new("test-call".into(), IceAgentConfig::default());
 
         let update = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-call".into(),
             reflexive_addr: Some("203.0.113.5:4433".into()),
             local_addrs: vec!["192.168.1.10:4433".into(), "10.0.0.5:4433".into()],
@@ -315,6 +321,7 @@ mod tests {
         let agent = IceAgent::new("test".into(), IceAgentConfig::default());
 
         let update = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test".into(),
             reflexive_addr: None,
             local_addrs: vec![],
@@ -333,6 +340,7 @@ mod tests {
         let agent = IceAgent::new("test".into(), IceAgentConfig::default());
 
         let update = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test".into(),
             reflexive_addr: Some("not-an-addr".into()),
             local_addrs: vec![
diff --git a/crates/wzp-client/src/reflect.rs b/crates/wzp-client/src/reflect.rs
index 9a28f2b..cf2f743 100644
--- a/crates/wzp-client/src/reflect.rs
+++ b/crates/wzp-client/src/reflect.rs
@@ -30,7 +30,7 @@ use std::net::SocketAddr;
 use std::time::{Duration, Instant};
 
 use serde::Serialize;
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_transport::{QuinnTransport, client_config, create_endpoint};
 
 /// Result of one probe against one relay. Always returned so the
@@ -123,6 +123,7 @@ pub async fn probe_reflect_addr(
         // path does in desktop/src-tauri/src/lib.rs register_signal.
         transport
             .send_signal(&SignalMessage::RegisterPresence {
+                version: default_signal_version(),
                 identity_pub: [0u8; 32],
                 signature: vec![],
                 alias: None,
@@ -150,7 +151,7 @@ pub async fn probe_reflect_addr(
             .map_err(|e| format!("send Reflect: {e}"))?;
 
         match transport.recv_signal().await {
-            Ok(Some(SignalMessage::ReflectResponse { observed_addr })) => {
+            Ok(Some(SignalMessage::ReflectResponse { observed_addr, .. })) => {
                 let parsed: SocketAddr = observed_addr
                     .parse()
                     .map_err(|e| format!("parse observed_addr {observed_addr:?}: {e}"))?;
diff --git a/crates/wzp-client/tests/handshake_integration.rs b/crates/wzp-client/tests/handshake_integration.rs
index 55dde70..8e1027a 100644
--- a/crates/wzp-client/tests/handshake_integration.rs
+++ b/crates/wzp-client/tests/handshake_integration.rs
@@ -11,7 +11,7 @@ use tokio::sync::mpsc;
 
 use wzp_proto::packet::MediaPacket;
 use wzp_proto::traits::{MediaTransport, PathQuality};
-use wzp_proto::{SignalMessage, TransportError};
+use wzp_proto::{SignalMessage, TransportError, default_signal_version};
 
 /// A mock transport backed by two mpsc channels (one per direction).
 ///
@@ -151,6 +151,7 @@ async fn handshake_rejects_tampered_signature() {
         let bad_signature = kx.sign(b"wrong-data-intentionally");
 
         let offer = SignalMessage::CallOffer {
+            version: default_signal_version(),
             identity_pub,
             ephemeral_pub,
             signature: bad_signature,
@@ -197,6 +198,7 @@ async fn client_receives_protocol_version_mismatch() {
 
         // Respond with ProtocolVersionMismatch.
         let mismatch = SignalMessage::Hangup {
+            version: default_signal_version(),
             reason: wzp_proto::HangupReason::ProtocolVersionMismatch {
                 server_supported: vec![3],
             },
diff --git a/crates/wzp-crypto/tests/featherchat_compat.rs b/crates/wzp-crypto/tests/featherchat_compat.rs
index e236d80..cb8cdcd 100644
--- a/crates/wzp-crypto/tests/featherchat_compat.rs
+++ b/crates/wzp-crypto/tests/featherchat_compat.rs
@@ -6,7 +6,7 @@
 //! 3. Auth: WZP auth module request/response matches FC's /v1/auth/validate contract
 //! 4. Mnemonic: BIP39 interop between both implementations
 
-use wzp_proto::KeyExchange;
+use wzp_proto::{KeyExchange, default_signal_version};
 
 // ─── Identity Compatibility (WZP-FC-8) ──────────────────────────────────────
 
@@ -114,6 +114,7 @@ fn mnemonic_strings_identical() {
 fn wzp_signal_serializes_into_fc_callsignal_payload() {
     // WZP creates a CallOffer SignalMessage
     let offer = wzp_proto::SignalMessage::CallOffer {
+        version: default_signal_version(),
         identity_pub: [1u8; 32],
         ephemeral_pub: [2u8; 32],
         signature: vec![3u8; 64],
@@ -180,6 +181,7 @@ fn wzp_signal_serializes_into_fc_callsignal_payload() {
 #[test]
 fn wzp_answer_round_trips_through_fc_callsignal() {
     let answer = wzp_proto::SignalMessage::CallAnswer {
+        version: default_signal_version(),
         identity_pub: [10u8; 32],
         ephemeral_pub: [20u8; 32],
         signature: vec![30u8; 64],
@@ -212,6 +214,7 @@ fn wzp_answer_round_trips_through_fc_callsignal() {
 #[test]
 fn wzp_hangup_round_trips_through_fc_callsignal() {
     let hangup = wzp_proto::SignalMessage::Hangup {
+        version: default_signal_version(),
         reason: wzp_proto::HangupReason::Normal,
         call_id: None,
     };
@@ -298,6 +301,7 @@ fn all_signal_types_map_correctly() {
     let cases: Vec<(wzp_proto::SignalMessage, &str)> = vec![
         (
             wzp_proto::SignalMessage::CallOffer {
+                version: default_signal_version(),
                 identity_pub: [0; 32],
                 ephemeral_pub: [0; 32],
                 signature: vec![],
@@ -310,6 +314,7 @@ fn all_signal_types_map_correctly() {
         ),
         (
             wzp_proto::SignalMessage::CallAnswer {
+                version: default_signal_version(),
                 identity_pub: [0; 32],
                 ephemeral_pub: [0; 32],
                 signature: vec![],
@@ -319,12 +324,14 @@ fn all_signal_types_map_correctly() {
         ),
         (
             wzp_proto::SignalMessage::IceCandidate {
+                version: default_signal_version(),
                 candidate: "candidate:1".to_string(),
             },
             "IceCandidate",
         ),
         (
             wzp_proto::SignalMessage::Hangup {
+                version: default_signal_version(),
                 reason: wzp_proto::HangupReason::Normal,
                 call_id: None,
             },
@@ -482,10 +489,11 @@ fn auth_response_with_eth_address() {
     assert!(!resp3.valid);
 }
 
-/// WZP-S-7: SignalMessage::AuthToken { token } exists and round-trips via serde.
+/// WZP-S-7: SignalMessage::AuthToken { version: default_signal_version(),  token } exists and round-trips via serde.
 #[test]
 fn wzp_proto_has_auth_token_variant() {
     let msg = wzp_proto::SignalMessage::AuthToken {
+        version: default_signal_version(),
         token: "fc-bearer-token-xyz".to_string(),
     };
 
@@ -496,7 +504,7 @@ fn wzp_proto_has_auth_token_variant() {
 
     // Deserialize back
     let decoded: wzp_proto::SignalMessage = serde_json::from_str(&json).unwrap();
-    if let wzp_proto::SignalMessage::AuthToken { token } = decoded {
+    if let wzp_proto::SignalMessage::AuthToken { token, .. } = decoded {
         assert_eq!(token, "fc-bearer-token-xyz");
     } else {
         panic!("expected AuthToken variant, got: {decoded:?}");
diff --git a/crates/wzp-proto/src/lib.rs b/crates/wzp-proto/src/lib.rs
index 346e81a..cdcf154 100644
--- a/crates/wzp-proto/src/lib.rs
+++ b/crates/wzp-proto/src/lib.rs
@@ -32,7 +32,7 @@ pub use media_type::MediaType;
 pub use packet::{
     CallAcceptMode, FRAME_TYPE_FULL, FRAME_TYPE_MINI, HangupReason, MediaHeader, MediaHeaderV2,
     MediaPacket, MiniFrameContext, MiniFrameContextV2, MiniHeader, MiniHeaderV2, PresenceUser,
-    QualityReport, RoomParticipant, SignalMessage, TrunkEntry, TrunkFrame,
+    QualityReport, RoomParticipant, SignalMessage, TrunkEntry, TrunkFrame, default_signal_version,
 };
 pub use quality::{AdaptiveQualityController, NetworkContext, Tier};
 pub use session::{Session, SessionEvent, SessionState};
diff --git a/crates/wzp-proto/src/packet.rs b/crates/wzp-proto/src/packet.rs
index 26b4cf0..a7b9f4c 100644
--- a/crates/wzp-proto/src/packet.rs
+++ b/crates/wzp-proto/src/packet.rs
@@ -540,10 +540,23 @@ impl MiniFrameContextV2 {
 /// Compatible with Warzone messenger's identity model:
 /// - Identity keys are Ed25519 (signing) + X25519 (encryption) derived from a 32-byte seed via HKDF
 /// - Fingerprint = SHA-256(Ed25519 public key)[:16]
+///
+/// **Version field:** every struct variant carries `version: u8` (default 1).
+/// Old payloads that omit `version` deserialize cleanly thanks to `#[serde(default)]`.
+///
+/// **Unknown variant handling:** `#[serde(other)]` is designed for
+/// string/integer enums with adjacent tagging, not for externally tagged enum
+/// variants. With externally tagged representation (the default for Rust enums),
+/// the variant name IS the tag, so there is no other value to catch. `bincode`
+/// in particular does not support `#[serde(other)]`. Unknown variants will
+/// naturally cause a deserialization error, which is the correct behavior for
+/// the signal protocol.
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub enum SignalMessage {
     /// Call initiation (analogous to Warzone's WireMessage::CallOffer).
     CallOffer {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Caller's Ed25519 identity public key (32 bytes).
         identity_pub: [u8; 32],
         /// Ephemeral X25519 public key for this call.
@@ -565,6 +578,8 @@ pub enum SignalMessage {
 
     /// Call acceptance (analogous to Warzone's WireMessage::CallAnswer).
     CallAnswer {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Callee's Ed25519 identity public key (32 bytes).
         identity_pub: [u8; 32],
         /// Callee's ephemeral X25519 public key.
@@ -577,11 +592,15 @@ pub enum SignalMessage {
 
     /// ICE candidate for NAT traversal.
     IceCandidate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         candidate: String,
     },
 
     /// Periodic rekeying (forward secrecy).
     Rekey {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// New ephemeral X25519 public key.
         new_ephemeral_pub: [u8; 32],
         /// Ed25519 signature over (new_ephemeral_pub || session_id).
@@ -590,6 +609,8 @@ pub enum SignalMessage {
 
     /// Quality/profile change request.
     QualityUpdate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         report: QualityReport,
         recommended_profile: crate::QualityProfile,
     },
@@ -601,6 +622,8 @@ pub enum SignalMessage {
     /// introducing this variant is backward-compatible with pre-Phase-4
     /// relays — they'll just log "unknown signal variant" on receipt.
     LossRecoveryUpdate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Total frames reconstructed via DRED since call start (monotonic).
         #[serde(default)]
         dred_reconstructions: u64,
@@ -616,9 +639,13 @@ pub enum SignalMessage {
 
     /// Connection keepalive / RTT measurement.
     Ping {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         timestamp_ms: u64,
     },
     Pong {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         timestamp_ms: u64,
     },
 
@@ -626,6 +653,8 @@ pub enum SignalMessage {
     /// with older clients that send Hangup without it — the relay falls
     /// back to ending ALL active calls for the sender in that case.
     Hangup {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         reason: HangupReason,
         #[serde(default, skip_serializing_if = "Option::is_none")]
         call_id: Option<String>,
@@ -634,6 +663,8 @@ pub enum SignalMessage {
     /// featherChat bearer token for relay authentication.
     /// Sent as the first signal message when --auth-url is configured.
     AuthToken {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         token: String,
     },
 
@@ -647,6 +678,8 @@ pub enum SignalMessage {
     Unmute,
     /// Transfer the call to another peer.
     Transfer {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         target_fingerprint: String,
         /// Optional relay address for the transfer target.
         relay_addr: Option<String>,
@@ -658,6 +691,8 @@ pub enum SignalMessage {
     /// Sent periodically over probe connections to share which fingerprints
     /// are connected to the sending relay.
     PresenceUpdate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Fingerprints currently connected to the sending relay.
         fingerprints: Vec<String>,
         /// Address of the sending relay (e.g., "192.168.1.10:4433").
@@ -666,11 +701,15 @@ pub enum SignalMessage {
 
     /// Ask a peer relay to look up a fingerprint in its registry.
     RouteQuery {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         fingerprint: String,
         ttl: u8,
     },
     /// Response to a route query.
     RouteResponse {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         fingerprint: String,
         found: bool,
         relay_chain: Vec<String>,
@@ -680,6 +719,8 @@ pub enum SignalMessage {
     /// Sent over a relay link (`_relay` SNI) to ask the peer relay to
     /// create a room and forward media for the given session.
     SessionForward {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         session_id: String,
         target_fingerprint: String,
         source_relay: String,
@@ -687,12 +728,16 @@ pub enum SignalMessage {
     /// Confirm that the forwarding session has been set up on the peer relay.
     /// The `room_name` tells the source relay which room to address media to.
     SessionForwardAck {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         session_id: String,
         room_name: String,
     },
 
     /// Room membership update — sent by relay to all participants when someone joins or leaves.
     RoomUpdate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Current participant count.
         count: u32,
         /// List of participants currently in the room.
@@ -702,12 +747,16 @@ pub enum SignalMessage {
     // ── Federation signals (relay-to-relay) ──
     /// Federation: initial handshake — the connecting relay identifies itself.
     FederationHello {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// TLS certificate fingerprint of the connecting relay.
         tls_fingerprint: String,
     },
 
     /// Federation: this relay now has local participants in a global room.
     GlobalRoomActive {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         room: String,
         /// Participants on the announcing relay (for federated presence).
         #[serde(default)]
@@ -716,6 +765,8 @@ pub enum SignalMessage {
 
     /// Federation: this relay's last local participant left a global room.
     GlobalRoomInactive {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         room: String,
     },
 
@@ -723,6 +774,8 @@ pub enum SignalMessage {
     /// Register on relay for direct calls. Sent on `_signal` connections
     /// after optional AuthToken.
     RegisterPresence {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Client's Ed25519 identity public key.
         identity_pub: [u8; 32],
         /// Signature over ("register-presence" || identity_pub).
@@ -733,6 +786,8 @@ pub enum SignalMessage {
 
     /// Relay confirms presence registration.
     RegisterPresenceAck {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         success: bool,
         #[serde(skip_serializing_if = "Option::is_none")]
         error: Option<String>,
@@ -750,6 +805,8 @@ pub enum SignalMessage {
 
     /// Direct call offer routed through the relay to a specific peer.
     DirectCallOffer {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// Caller's fingerprint.
         caller_fingerprint: String,
         /// Caller's display name.
@@ -798,6 +855,8 @@ pub enum SignalMessage {
 
     /// Callee's response to a direct call.
     DirectCallAnswer {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// How the callee accepts (or rejects).
         accept_mode: CallAcceptMode,
@@ -838,6 +897,8 @@ pub enum SignalMessage {
 
     /// Relay tells both parties: media room is ready.
     CallSetup {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// Room name on the relay for the media session (e.g., "_call:a1b2c3d4").
         room: String,
@@ -871,6 +932,8 @@ pub enum SignalMessage {
 
     /// Ringing notification (relay → caller, callee received the offer).
     CallRinging {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
     },
 
@@ -893,6 +956,8 @@ pub enum SignalMessage {
     /// for IPv4, "[::1]:p" for IPv6. Clients parse it with
     /// `SocketAddr::from_str`.
     ReflectResponse {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         observed_addr: String,
     },
 
@@ -910,6 +975,8 @@ pub enum SignalMessage {
     /// and the other picks Relay — they now agree on the path
     /// before any media flows.
     MediaPathReport {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// Did the direct QUIC connection (P2P dial or accept)
         /// complete successfully on this side?
@@ -931,6 +998,8 @@ pub enum SignalMessage {
     /// — peers ignore updates with a generation <= their last-seen
     /// generation to handle reordering.
     CandidateUpdate {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// New server-reflexive address (STUN-discovered or relay-reflected).
         #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -951,6 +1020,8 @@ pub enum SignalMessage {
     /// and recent port sequence so the peer can predict which port
     /// to dial.
     HardNatProbe {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// Last observed external ports (most recent first).
         /// Typically 3-5 entries from sequential STUN probes.
@@ -968,6 +1039,8 @@ pub enum SignalMessage {
     /// ports it has open. The Dialer then sprays QUIC connects to
     /// these ports (and optionally random ports) on the Acceptor's IP.
     HardNatBirthdayStart {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// Number of sockets the Acceptor opened.
         acceptor_port_count: u16,
@@ -995,6 +1068,8 @@ pub enum SignalMessage {
     /// A→B→A echo loops; proper TTL + dedup will land when
     /// multi-hop federation is added (Phase 4.2).
     FederatedSignalForward {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// The signal message being forwarded
         /// (`DirectCallOffer`, `DirectCallAnswer`, `CallRinging`,
         /// `Hangup`, ...). Boxed because `SignalMessage` is
@@ -1011,6 +1086,8 @@ pub enum SignalMessage {
     /// Relay-initiated quality directive: all participants should switch
     /// to the recommended profile to match the weakest link.
     QualityDirective {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         recommended_profile: crate::QualityProfile,
         #[serde(default, skip_serializing_if = "Option::is_none")]
         reason: Option<String>,
@@ -1021,6 +1098,8 @@ pub enum SignalMessage {
     /// users to all connected clients. Sent on every register/
     /// deregister so clients can maintain a live lobby user list.
     PresenceList {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         /// List of online users. Each entry is { fingerprint, alias }.
         users: Vec<PresenceUser>,
     },
@@ -1031,6 +1110,8 @@ pub enum SignalMessage {
     /// conditions. Used for consensual upgrades that require both
     /// sides to agree (e.g., switching from Opus24k to Studio48k).
     UpgradeProposal {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// Unique ID for this proposal (to match response).
         proposal_id: String,
@@ -1045,6 +1126,8 @@ pub enum SignalMessage {
 
     /// Response to an UpgradeProposal.
     UpgradeResponse {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         proposal_id: String,
         /// true = accepted, both sides switch. false = rejected.
@@ -1057,6 +1140,8 @@ pub enum SignalMessage {
     /// Confirmation that the upgrade is committed — both sides
     /// should switch encoder at the next frame boundary.
     UpgradeConfirm {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         proposal_id: String,
         confirmed_profile: crate::QualityProfile,
@@ -1067,6 +1152,8 @@ pub enum SignalMessage {
     /// encoding where each side uses the best quality its connection
     /// supports, rather than forcing all to the weakest link.
     QualityCapability {
+        #[serde(default = "default_signal_version")]
+        version: u8,
         call_id: String,
         /// The best profile this peer can sustain based on its
         /// current network conditions.
@@ -1083,7 +1170,7 @@ pub enum SignalMessage {
     /// carrying ACK/NACK vectors and a REMB-style bandwidth estimate.
     TransportFeedback {
         /// Feedback format version (default 1).
-        #[serde(default)]
+        #[serde(default = "default_signal_version")]
         version: u8,
         /// Which media stream this feedback applies to.
         stream_id: u8,
@@ -1132,6 +1219,10 @@ pub fn default_proto_version() -> u8 {
 pub fn default_supported_versions() -> Vec<u8> {
     vec![2]
 }
+/// Default signal message version (v1).
+pub fn default_signal_version() -> u8 {
+    1
+}
 
 /// Reasons for ending a call.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
@@ -1304,12 +1395,13 @@ mod tests {
         // for v6 and the client side has to parse that back.
         for addr in ["192.0.2.17:4433", "[2001:db8::1]:4433", "127.0.0.1:54321"] {
             let resp = SignalMessage::ReflectResponse {
+                version: default_signal_version(),
                 observed_addr: addr.to_string(),
             };
             let json = serde_json::to_string(&resp).unwrap();
             let decoded: SignalMessage = serde_json::from_str(&json).unwrap();
             match decoded {
-                SignalMessage::ReflectResponse { observed_addr } => {
+                SignalMessage::ReflectResponse { observed_addr, .. } => {
                     assert_eq!(observed_addr, addr);
                     // Must parse back to a SocketAddr cleanly.
                     let _parsed: std::net::SocketAddr = observed_addr
@@ -1326,6 +1418,7 @@ mod tests {
         // Wrap a DirectCallOffer inside FederatedSignalForward and
         // prove both directions of serde preserve every field.
         let inner = SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: "alice".into(),
             caller_alias: Some("Alice".into()),
             target_fingerprint: "bob".into(),
@@ -1340,6 +1433,7 @@ mod tests {
             caller_build_version: None,
         };
         let forward = SignalMessage::FederatedSignalForward {
+            version: default_signal_version(),
             inner: Box::new(inner),
             origin_relay_fp: "relay-a-tls-fp".into(),
         };
@@ -1349,6 +1443,7 @@ mod tests {
             SignalMessage::FederatedSignalForward {
                 inner,
                 origin_relay_fp,
+                ..
             } => {
                 assert_eq!(origin_relay_fp, "relay-a-tls-fp");
                 match *inner {
@@ -1375,6 +1470,7 @@ mod tests {
         // we intend to forward survives being boxed + re-serialized.
         let cases: Vec<SignalMessage> = vec![
             SignalMessage::DirectCallAnswer {
+                version: default_signal_version(),
                 call_id: "c1".into(),
                 accept_mode: CallAcceptMode::AcceptTrusted,
                 identity_pub: None,
@@ -1387,9 +1483,11 @@ mod tests {
                 callee_build_version: None,
             },
             SignalMessage::CallRinging {
+                version: default_signal_version(),
                 call_id: "c1".into(),
             },
             SignalMessage::Hangup {
+                version: default_signal_version(),
                 reason: HangupReason::Normal,
                 call_id: None,
             },
@@ -1397,6 +1495,7 @@ mod tests {
         for inner in cases {
             let inner_disc = std::mem::discriminant(&inner);
             let forward = SignalMessage::FederatedSignalForward {
+                version: default_signal_version(),
                 inner: Box::new(inner),
                 origin_relay_fp: "r".into(),
             };
@@ -1415,6 +1514,7 @@ mod tests {
     fn hole_punching_optional_fields_roundtrip() {
         // DirectCallOffer with Some(caller_reflexive_addr)
         let offer = SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: "alice".into(),
             caller_alias: None,
             target_fingerprint: "bob".into(),
@@ -1448,6 +1548,7 @@ mod tests {
         // OMIT the field from the JSON so older relays that don't
         // know about caller_reflexive_addr don't see it.
         let offer_none = SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: "alice".into(),
             caller_alias: None,
             target_fingerprint: "bob".into(),
@@ -1469,6 +1570,7 @@ mod tests {
 
         // DirectCallAnswer with callee_reflexive_addr.
         let answer = SignalMessage::DirectCallAnswer {
+            version: default_signal_version(),
             call_id: "c1".into(),
             accept_mode: CallAcceptMode::AcceptTrusted,
             identity_pub: None,
@@ -1494,6 +1596,7 @@ mod tests {
 
         // CallSetup with peer_direct_addr.
         let setup = SignalMessage::CallSetup {
+            version: default_signal_version(),
             call_id: "c1".into(),
             room: "call-c1".into(),
             relay_addr: "203.0.113.5:4433".into(),
@@ -1566,14 +1669,17 @@ mod tests {
         // test a sample of the pre-existing ones.
         let cases = vec![
             SignalMessage::Ping {
+                version: default_signal_version(),
                 timestamp_ms: 12345,
             },
             SignalMessage::Hold,
             SignalMessage::Hangup {
+                version: default_signal_version(),
                 reason: HangupReason::Normal,
                 call_id: None,
             },
             SignalMessage::CallRinging {
+                version: default_signal_version(),
                 call_id: "abcd".into(),
             },
         ];
@@ -1614,6 +1720,7 @@ mod tests {
     #[test]
     fn transfer_serialize() {
         let transfer = SignalMessage::Transfer {
+            version: default_signal_version(),
             target_fingerprint: "abc123".to_string(),
             relay_addr: Some("relay.example.com:4433".to_string()),
         };
@@ -1623,6 +1730,7 @@ mod tests {
             SignalMessage::Transfer {
                 target_fingerprint,
                 relay_addr,
+                ..
             } => {
                 assert_eq!(target_fingerprint, "abc123");
                 assert_eq!(relay_addr.unwrap(), "relay.example.com:4433");
@@ -1632,6 +1740,7 @@ mod tests {
 
         // Also test with relay_addr = None
         let transfer_no_relay = SignalMessage::Transfer {
+            version: default_signal_version(),
             target_fingerprint: "def456".to_string(),
             relay_addr: None,
         };
@@ -1641,6 +1750,7 @@ mod tests {
             SignalMessage::Transfer {
                 target_fingerprint,
                 relay_addr,
+                ..
             } => {
                 assert_eq!(target_fingerprint, "def456");
                 assert!(relay_addr.is_none());
@@ -1660,6 +1770,7 @@ mod tests {
     #[test]
     fn presence_update_signal_roundtrip() {
         let msg = SignalMessage::PresenceUpdate {
+            version: default_signal_version(),
             fingerprints: vec!["aabb".to_string(), "ccdd".to_string()],
             relay_addr: "10.0.0.1:4433".to_string(),
         };
@@ -1669,6 +1780,7 @@ mod tests {
             SignalMessage::PresenceUpdate {
                 fingerprints,
                 relay_addr,
+                ..
             } => {
                 assert_eq!(fingerprints.len(), 2);
                 assert!(fingerprints.contains(&"aabb".to_string()));
@@ -1680,6 +1792,7 @@ mod tests {
 
         // Empty fingerprints list
         let msg_empty = SignalMessage::PresenceUpdate {
+            version: default_signal_version(),
             fingerprints: vec![],
             relay_addr: "10.0.0.2:4433".to_string(),
         };
@@ -1689,6 +1802,7 @@ mod tests {
             SignalMessage::PresenceUpdate {
                 fingerprints,
                 relay_addr,
+                ..
             } => {
                 assert!(fingerprints.is_empty());
                 assert_eq!(relay_addr, "10.0.0.2:4433");
@@ -1999,6 +2113,7 @@ mod tests {
     #[test]
     fn quality_directive_roundtrip() {
         let msg = SignalMessage::QualityDirective {
+            version: default_signal_version(),
             recommended_profile: crate::QualityProfile::DEGRADED,
             reason: Some("weakest link degraded".into()),
         };
@@ -2008,6 +2123,7 @@ mod tests {
             SignalMessage::QualityDirective {
                 recommended_profile,
                 reason,
+                ..
             } => {
                 assert_eq!(recommended_profile.codec, CodecId::Opus6k);
                 assert_eq!(reason.as_deref(), Some("weakest link degraded"));
@@ -2019,6 +2135,7 @@ mod tests {
     #[test]
     fn quality_directive_without_reason_roundtrip() {
         let msg = SignalMessage::QualityDirective {
+            version: default_signal_version(),
             recommended_profile: crate::QualityProfile::GOOD,
             reason: None,
         };
@@ -2078,6 +2195,7 @@ mod tests {
     #[test]
     fn upgrade_proposal_roundtrip() {
         let msg = SignalMessage::UpgradeProposal {
+            version: default_signal_version(),
             call_id: "c1".into(),
             proposal_id: "p1".into(),
             proposed_profile: crate::QualityProfile::STUDIO_48K,
@@ -2102,6 +2220,7 @@ mod tests {
     #[test]
     fn upgrade_response_roundtrip() {
         let msg = SignalMessage::UpgradeResponse {
+            version: default_signal_version(),
             call_id: "c1".into(),
             proposal_id: "p1".into(),
             accepted: true,
@@ -2118,6 +2237,7 @@ mod tests {
     #[test]
     fn upgrade_confirm_roundtrip() {
         let msg = SignalMessage::UpgradeConfirm {
+            version: default_signal_version(),
             call_id: "c1".into(),
             proposal_id: "p1".into(),
             confirmed_profile: crate::QualityProfile::STUDIO_64K,
@@ -2137,6 +2257,7 @@ mod tests {
     #[test]
     fn quality_capability_roundtrip() {
         let msg = SignalMessage::QualityCapability {
+            version: default_signal_version(),
             call_id: "c1".into(),
             max_profile: crate::QualityProfile::GOOD,
             loss_pct: Some(2.5),
@@ -2162,6 +2283,7 @@ mod tests {
     #[test]
     fn candidate_update_roundtrip() {
         let msg = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "test-123".into(),
             reflexive_addr: Some("203.0.113.5:4433".into()),
             local_addrs: vec!["192.168.1.10:4433".into(), "10.0.0.5:4433".into()],
@@ -2177,6 +2299,7 @@ mod tests {
                 local_addrs,
                 mapped_addr,
                 generation,
+                ..
             } => {
                 assert_eq!(call_id, "test-123");
                 assert_eq!(reflexive_addr.as_deref(), Some("203.0.113.5:4433"));
@@ -2191,6 +2314,7 @@ mod tests {
     #[test]
     fn candidate_update_minimal_roundtrip() {
         let msg = SignalMessage::CandidateUpdate {
+            version: default_signal_version(),
             call_id: "c".into(),
             reflexive_addr: None,
             local_addrs: vec![],
@@ -2215,6 +2339,7 @@ mod tests {
     #[test]
     fn offer_with_mapped_addr_roundtrip() {
         let msg = SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: "alice".into(),
             caller_alias: None,
             target_fingerprint: "bob".into(),
@@ -2246,6 +2371,7 @@ mod tests {
     #[test]
     fn offer_without_mapped_addr_omits_field() {
         let msg = SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: "alice".into(),
             caller_alias: None,
             target_fingerprint: "bob".into(),
@@ -2266,6 +2392,7 @@ mod tests {
     #[test]
     fn answer_with_mapped_addr_roundtrip() {
         let msg = SignalMessage::DirectCallAnswer {
+            version: default_signal_version(),
             call_id: "c1".into(),
             accept_mode: CallAcceptMode::AcceptTrusted,
             identity_pub: None,
@@ -2292,6 +2419,7 @@ mod tests {
     #[test]
     fn setup_with_mapped_addr_roundtrip() {
         let msg = SignalMessage::CallSetup {
+            version: default_signal_version(),
             call_id: "c1".into(),
             room: "room".into(),
             relay_addr: "1.2.3.4:5".into(),
@@ -2368,6 +2496,7 @@ mod tests {
     #[test]
     fn register_presence_ack_with_new_fields_roundtrip() {
         let msg = SignalMessage::RegisterPresenceAck {
+            version: default_signal_version(),
             success: true,
             error: None,
             relay_build: Some("abc123".into()),
@@ -2443,6 +2572,7 @@ mod tests {
                 nacked_seqs,
                 remb_bps,
                 recv_time_us,
+                ..
             } => {
                 assert_eq!(version, 1);
                 assert_eq!(stream_id, 0);
@@ -2475,7 +2605,76 @@ mod tests {
         let decoded: SignalMessage = serde_json::from_str(json).unwrap();
         match decoded {
             SignalMessage::TransportFeedback { version, .. } => {
-                assert_eq!(version, 0, "serde default makes omitted version 0");
+                assert_eq!(version, 1, "serde default makes omitted version 1");
+            }
+            _ => panic!("wrong variant"),
+        }
+    }
+
+    #[test]
+    fn old_payload_without_version_deserializes() {
+        // CallOffer without version field — old client sending to new receiver.
+        let json = r#"{
+            "CallOffer": {
+                "identity_pub": [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],
+                "ephemeral_pub": [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],
+                "signature": [],
+                "supported_profiles": [],
+                "alias": null,
+                "protocol_version": 2,
+                "supported_versions": [2]
+            }
+        }"#;
+        let decoded: SignalMessage = serde_json::from_str(json).unwrap();
+        match decoded {
+            SignalMessage::CallOffer {
+                version,
+                protocol_version,
+                ..
+            } => {
+                assert_eq!(version, 1, "missing version defaults to 1");
+                assert_eq!(protocol_version, 2);
+            }
+            _ => panic!("wrong variant"),
+        }
+
+        // Ping without version field.
+        let json = r#"{"Ping": {"timestamp_ms": 1234}}"#;
+        let decoded: SignalMessage = serde_json::from_str(json).unwrap();
+        match decoded {
+            SignalMessage::Ping {
+                version,
+                timestamp_ms,
+            } => {
+                assert_eq!(version, 1, "missing version defaults to 1");
+                assert_eq!(timestamp_ms, 1234);
+            }
+            _ => panic!("wrong variant"),
+        }
+
+        // Hangup without version field.
+        let json = r#"{"Hangup": {"reason": "Normal", "call_id": null}}"#;
+        let decoded: SignalMessage = serde_json::from_str(json).unwrap();
+        match decoded {
+            SignalMessage::Hangup { version, .. } => {
+                assert_eq!(version, 1, "missing version defaults to 1");
+            }
+            _ => panic!("wrong variant"),
+        }
+    }
+
+    #[test]
+    fn new_payload_with_version_deserializes() {
+        // Payload that explicitly includes version = 2.
+        let json = r#"{"Ping": {"version": 2, "timestamp_ms": 5678}}"#;
+        let decoded: SignalMessage = serde_json::from_str(json).unwrap();
+        match decoded {
+            SignalMessage::Ping {
+                version,
+                timestamp_ms,
+            } => {
+                assert_eq!(version, 2, "explicit version is preserved");
+                assert_eq!(timestamp_ms, 5678);
             }
             _ => panic!("wrong variant"),
         }
diff --git a/crates/wzp-relay/src/federation.rs b/crates/wzp-relay/src/federation.rs
index 27773b7..2e36b09 100644
--- a/crates/wzp-relay/src/federation.rs
+++ b/crates/wzp-relay/src/federation.rs
@@ -15,7 +15,7 @@ use sha2::{Digest, Sha256};
 use tokio::sync::Mutex;
 use tracing::{error, info, warn};
 
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_transport::QuinnTransport;
 
 use crate::config::{PeerConfig, TrustedConfig};
@@ -520,7 +520,11 @@ async fn run_room_event_dispatcher(
                 if fm.is_global_room(&room) {
                     let participants = fm.room_mgr.local_participant_list(&room);
                     info!(room = %room, count = participants.len(), "global room now active, announcing to peers");
-                    let msg = SignalMessage::GlobalRoomActive { room, participants };
+                    let msg = SignalMessage::GlobalRoomActive {
+                        version: default_signal_version(),
+                        room,
+                        participants,
+                    };
                     let transports: Vec<Arc<QuinnTransport>> = {
                         let links = fm.peer_links.lock().await;
                         links.values().map(|l| l.transport.clone()).collect()
@@ -533,7 +537,10 @@ async fn run_room_event_dispatcher(
             Ok(RoomEvent::LocalLeave { room }) => {
                 if fm.is_global_room(&room) {
                     info!(room = %room, "global room now inactive, announcing to peers");
-                    let msg = SignalMessage::GlobalRoomInactive { room };
+                    let msg = SignalMessage::GlobalRoomInactive {
+                        version: default_signal_version(),
+                        room,
+                    };
                     let transports: Vec<Arc<QuinnTransport>> = {
                         let links = fm.peer_links.lock().await;
                         links.values().map(|l| l.transport.clone()).collect()
@@ -609,6 +616,7 @@ async fn run_stale_presence_sweeper(fm: Arc<FederationManager>) {
                     let mut seen = HashSet::new();
                     all_participants.retain(|p| seen.insert(p.fingerprint.clone()));
                     let update = SignalMessage::RoomUpdate {
+                        version: default_signal_version(),
                         count: all_participants.len() as u32,
                         participants: all_participants,
                     };
@@ -659,6 +667,7 @@ async fn connect_to_peer(
 
     // Send hello with our TLS fingerprint
     let hello = SignalMessage::FederationHello {
+        version: default_signal_version(),
         tls_fingerprint: fm.local_tls_fp.clone(),
     };
     transport
@@ -710,6 +719,7 @@ async fn run_federation_link(
                 let participants = fm.room_mgr.local_participant_list(room_name);
                 info!(peer = %peer_label, room = %room_name, participants = participants.len(), "announcing local global room to new peer");
                 msgs.push(SignalMessage::GlobalRoomActive {
+                    version: default_signal_version(),
                     room: room_name.clone(),
                     participants,
                 });
@@ -724,6 +734,7 @@ async fn run_federation_link(
                     if fm.is_global_room(room) {
                         info!(peer = %peer_label, room = %room, via = %link.label, "propagating remote room to new peer");
                         msgs.push(SignalMessage::GlobalRoomActive {
+                            version: default_signal_version(),
                             room: room.clone(),
                             participants: participants.clone(),
                         });
@@ -837,7 +848,9 @@ async fn handle_signal(
     }
 
     match msg {
-        SignalMessage::GlobalRoomActive { room, participants } => {
+        SignalMessage::GlobalRoomActive {
+            room, participants, ..
+        } => {
             if fm.is_global_room(&room) {
                 info!(peer = %peer_label, room = %room, remote_participants = participants.len(), "peer has global room active");
                 let mut links = fm.peer_links.lock().await;
@@ -882,6 +895,7 @@ async fn handle_signal(
                         let _ = link
                             .transport
                             .send_signal(&SignalMessage::GlobalRoomActive {
+                                version: default_signal_version(),
                                 room: room.clone(),
                                 participants: tagged_for_propagation.clone(),
                             })
@@ -923,6 +937,7 @@ async fn handle_signal(
                         let mut seen = HashSet::new();
                         all_participants.retain(|p| seen.insert(p.fingerprint.clone()));
                         let update = SignalMessage::RoomUpdate {
+                            version: default_signal_version(),
                             count: all_participants.len() as u32,
                             participants: all_participants,
                         };
@@ -933,7 +948,7 @@ async fn handle_signal(
                 }
             }
         }
-        SignalMessage::GlobalRoomInactive { room } => {
+        SignalMessage::GlobalRoomInactive { room, .. } => {
             info!(peer = %peer_label, room = %room, "peer global room now inactive");
             let mut links = fm.peer_links.lock().await;
             if let Some(link) = links.get_mut(peer_fp) {
@@ -999,6 +1014,7 @@ async fn handle_signal(
                     }
                 }
                 let msg = SignalMessage::GlobalRoomActive {
+                    version: default_signal_version(),
                     room: room.clone(),
                     participants: updated_participants,
                 };
@@ -1007,7 +1023,10 @@ async fn handle_signal(
                 }
             } else {
                 // No participants left anywhere — propagate inactive
-                let msg = SignalMessage::GlobalRoomInactive { room: room.clone() };
+                let msg = SignalMessage::GlobalRoomInactive {
+                    version: default_signal_version(),
+                    room: room.clone(),
+                };
                 for transport in &peer_sends {
                     let _ = transport.send_signal(&msg).await;
                 }
@@ -1025,6 +1044,7 @@ async fn handle_signal(
                     let mut seen = HashSet::new();
                     all_participants.retain(|p| seen.insert(p.fingerprint.clone()));
                     let update = SignalMessage::RoomUpdate {
+                        version: default_signal_version(),
                         count: all_participants.len() as u32,
                         participants: all_participants,
                     };
@@ -1050,6 +1070,7 @@ async fn handle_signal(
         SignalMessage::FederatedSignalForward {
             inner,
             origin_relay_fp,
+            ..
         } => {
             if origin_relay_fp == fm.local_tls_fp {
                 tracing::debug!(
diff --git a/crates/wzp-relay/src/handshake.rs b/crates/wzp-relay/src/handshake.rs
index df1bcc1..e4e2379 100644
--- a/crates/wzp-relay/src/handshake.rs
+++ b/crates/wzp-relay/src/handshake.rs
@@ -4,7 +4,7 @@
 //! recv `CallOffer` → verify → generate ephemeral → derive session → send `CallAnswer`.
 
 use wzp_crypto::{CryptoSession, KeyExchange, WarzoneKeyExchange};
-use wzp_proto::{MediaTransport, QualityProfile, SignalMessage};
+use wzp_proto::{MediaTransport, QualityProfile, SignalMessage, default_signal_version};
 
 /// Accept the relay (callee) side of the cryptographic handshake.
 ///
@@ -51,6 +51,7 @@ pub async fn accept_handshake(
             alias,
             protocol_version,
             supported_versions: _,
+            ..
         } => (
             identity_pub,
             ephemeral_pub,
@@ -70,6 +71,7 @@ pub async fn accept_handshake(
     // 1a. Protocol version check — we only speak v2.
     if protocol_version != 2 {
         let mismatch = SignalMessage::Hangup {
+            version: default_signal_version(),
             reason: wzp_proto::HangupReason::ProtocolVersionMismatch {
                 server_supported: vec![2],
             },
@@ -108,6 +110,7 @@ pub async fn accept_handshake(
 
     // 6. Send CallAnswer
     let answer = SignalMessage::CallAnswer {
+        version: default_signal_version(),
         identity_pub,
         ephemeral_pub,
         signature,
diff --git a/crates/wzp-relay/src/main.rs b/crates/wzp-relay/src/main.rs
index 2435e88..333c9a6 100644
--- a/crates/wzp-relay/src/main.rs
+++ b/crates/wzp-relay/src/main.rs
@@ -16,7 +16,7 @@ use clap::Parser;
 use tokio::sync::Mutex;
 use tracing::{debug, error, info, warn};
 
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_relay::config::RelayConfig;
 use wzp_relay::metrics::RelayMetrics;
 use wzp_relay::pipeline::{PipelineConfig, RelayPipeline};
@@ -640,6 +640,7 @@ async fn main() -> anyhow::Result<()> {
                                 .send_to(
                                     &caller_fp,
                                     &SignalMessage::Hangup {
+                                        version: default_signal_version(),
                                         reason: wzp_proto::HangupReason::Normal,
                                         call_id: None,
                                     },
@@ -685,6 +686,7 @@ async fn main() -> anyhow::Result<()> {
 
                         // Emit the LOCAL CallSetup to our local caller.
                         let setup = SignalMessage::CallSetup {
+                            version: default_signal_version(),
                             call_id: call_id.clone(),
                             room: room_name.clone(),
                             relay_addr: advertised_addr_d.clone(),
@@ -703,7 +705,7 @@ async fn main() -> anyhow::Result<()> {
                         );
                     }
 
-                    SignalMessage::CallRinging { ref call_id } => {
+                    SignalMessage::CallRinging { ref call_id, .. } => {
                         // Forward to local caller for "ringing..." UX.
                         let caller_fp = {
                             let reg = call_registry_d.lock().await;
@@ -866,9 +868,12 @@ async fn main() -> anyhow::Result<()> {
                 info!(%addr, "probe connection detected, entering Ping/Pong + presence responder");
                 loop {
                     match transport.recv_signal().await {
-                        Ok(Some(wzp_proto::SignalMessage::Ping { timestamp_ms })) => {
+                        Ok(Some(wzp_proto::SignalMessage::Ping { timestamp_ms, .. })) => {
                             if let Err(e) = transport
-                                .send_signal(&wzp_proto::SignalMessage::Pong { timestamp_ms })
+                                .send_signal(&wzp_proto::SignalMessage::Pong {
+                                    version: default_signal_version(),
+                                    timestamp_ms,
+                                })
                                 .await
                             {
                                 error!(%addr, "probe pong send error: {e}");
@@ -878,6 +883,7 @@ async fn main() -> anyhow::Result<()> {
                         Ok(Some(wzp_proto::SignalMessage::PresenceUpdate {
                             fingerprints,
                             relay_addr,
+                            ..
                         })) => {
                             // A peer relay is telling us which fingerprints it has
                             let peer_addr: std::net::SocketAddr =
@@ -894,6 +900,7 @@ async fn main() -> anyhow::Result<()> {
                                 reg.local_fingerprints().into_iter().collect()
                             };
                             let reply = wzp_proto::SignalMessage::PresenceUpdate {
+                                version: default_signal_version(),
                                 fingerprints: local_fps,
                                 relay_addr: addr.to_string(),
                             };
@@ -902,7 +909,9 @@ async fn main() -> anyhow::Result<()> {
                                 break;
                             }
                         }
-                        Ok(Some(wzp_proto::SignalMessage::RouteQuery { fingerprint, ttl })) => {
+                        Ok(Some(wzp_proto::SignalMessage::RouteQuery {
+                            fingerprint, ttl, ..
+                        })) => {
                             // Look up the fingerprint in our local registry
                             let reg = presence.lock().await;
                             let route = route_resolver.resolve(&reg, &fingerprint);
@@ -930,6 +939,7 @@ async fn main() -> anyhow::Result<()> {
                             };
 
                             let reply = wzp_proto::SignalMessage::RouteResponse {
+                                version: default_signal_version(),
                                 fingerprint,
                                 found,
                                 relay_chain,
@@ -968,6 +978,7 @@ async fn main() -> anyhow::Result<()> {
                     {
                         Ok(Ok(Some(wzp_proto::SignalMessage::FederationHello {
                             tls_fingerprint,
+                            ..
                         }))) => tls_fingerprint,
                         _ => {
                             warn!(%addr, "federation: no hello received, closing");
@@ -1004,7 +1015,7 @@ async fn main() -> anyhow::Result<()> {
                 // Optional auth
                 let auth_fp: Option<String> = if let Some(ref url) = auth_url {
                     match transport.recv_signal().await {
-                        Ok(Some(SignalMessage::AuthToken { token })) => {
+                        Ok(Some(SignalMessage::AuthToken { token, .. })) => {
                             match wzp_relay::auth::validate_token(url, &token).await {
                                 Ok(client) => Some(client.fingerprint),
                                 Err(e) => {
@@ -1033,6 +1044,7 @@ async fn main() -> anyhow::Result<()> {
                         identity_pub,
                         signature: _,
                         alias,
+                        ..
                     }))) => {
                         // Compute fingerprint: SHA-256(Ed25519 pub key)[:16], same as Fingerprint type
                         let fp = {
@@ -1067,6 +1079,7 @@ async fn main() -> anyhow::Result<()> {
                 // Send ack
                 let _ = transport
                     .send_signal(&SignalMessage::RegisterPresenceAck {
+                        version: default_signal_version(),
                         success: true,
                         error: None,
                         relay_build: Some(BUILD_GIT_HASH.to_string()),
@@ -1126,6 +1139,7 @@ async fn main() -> anyhow::Result<()> {
                                         // federation has a matching entry.
                                         let forwarded = if let Some(ref fm) = federation_mgr {
                                             let forward = SignalMessage::FederatedSignalForward {
+                                                version: default_signal_version(),
                                                 inner: Box::new(msg.clone()),
                                                 origin_relay_fp: tls_fp.clone(),
                                             };
@@ -1149,6 +1163,7 @@ async fn main() -> anyhow::Result<()> {
                                             info!(%addr, target = %target_fp, "call target not online (no federation route)");
                                             let _ = transport
                                                 .send_signal(&SignalMessage::Hangup {
+                                                    version: default_signal_version(),
                                                     reason: wzp_proto::HangupReason::Normal,
                                                     call_id: None,
                                                 })
@@ -1193,6 +1208,7 @@ async fn main() -> anyhow::Result<()> {
                                         // federated delivery is in flight.
                                         let _ = transport
                                             .send_signal(&SignalMessage::CallRinging {
+                                                version: default_signal_version(),
                                                 call_id: call_id.clone(),
                                             })
                                             .await;
@@ -1236,6 +1252,7 @@ async fn main() -> anyhow::Result<()> {
                                     drop(hub);
                                     let _ = transport
                                         .send_signal(&SignalMessage::CallRinging {
+                                            version: default_signal_version(),
                                             call_id: call_id.clone(),
                                         })
                                         .await;
@@ -1293,11 +1310,13 @@ async fn main() -> anyhow::Result<()> {
                                         if let Some(ref origin_fp) = peer_relay_fp {
                                             if let Some(ref fm) = federation_mgr {
                                                 let hangup = SignalMessage::Hangup {
+                                                    version: default_signal_version(),
                                                     reason: wzp_proto::HangupReason::Normal,
                                                     call_id: Some(call_id.clone()),
                                                 };
                                                 let forward =
                                                     SignalMessage::FederatedSignalForward {
+                                                        version: default_signal_version(),
                                                         inner: Box::new(hangup),
                                                         origin_relay_fp: tls_fp.clone(),
                                                     };
@@ -1314,6 +1333,7 @@ async fn main() -> anyhow::Result<()> {
                                                 .send_to(
                                                     &peer_fp,
                                                     &SignalMessage::Hangup {
+                                                        version: default_signal_version(),
                                                         reason: wzp_proto::HangupReason::Normal,
                                                         call_id: Some(call_id.clone()),
                                                     },
@@ -1390,6 +1410,7 @@ async fn main() -> anyhow::Result<()> {
                                             if let Some(ref fm) = federation_mgr {
                                                 let forward =
                                                     SignalMessage::FederatedSignalForward {
+                                                        version: default_signal_version(),
                                                         inner: Box::new(msg.clone()),
                                                         origin_relay_fp: tls_fp.clone(),
                                                     };
@@ -1407,6 +1428,7 @@ async fn main() -> anyhow::Result<()> {
                                             }
 
                                             let setup_for_callee = SignalMessage::CallSetup {
+                                                version: default_signal_version(),
                                                 call_id: call_id.clone(),
                                                 room: room.clone(),
                                                 relay_addr: relay_addr_for_setup,
@@ -1429,6 +1451,7 @@ async fn main() -> anyhow::Result<()> {
                                             // cross-wired candidates (Phase 5.5 ICE
                                             // + Phase 8 port-mapped addrs).
                                             let setup_for_caller = SignalMessage::CallSetup {
+                                                version: default_signal_version(),
                                                 call_id: call_id.clone(),
                                                 room: room.clone(),
                                                 relay_addr: relay_addr_for_setup.clone(),
@@ -1437,6 +1460,7 @@ async fn main() -> anyhow::Result<()> {
                                                 peer_mapped_addr: callee_mapped,
                                             };
                                             let setup_for_callee = SignalMessage::CallSetup {
+                                                version: default_signal_version(),
                                                 call_id: call_id.clone(),
                                                 room: room.clone(),
                                                 relay_addr: relay_addr_for_setup,
@@ -1524,6 +1548,7 @@ async fn main() -> anyhow::Result<()> {
                                             if let Some(ref fm) = federation_mgr {
                                                 let forward =
                                                     SignalMessage::FederatedSignalForward {
+                                                        version: default_signal_version(),
                                                         inner: Box::new(msg.clone()),
                                                         origin_relay_fp: tls_fp.clone(),
                                                     };
@@ -1568,6 +1593,7 @@ async fn main() -> anyhow::Result<()> {
                                             if let Some(ref fm) = federation_mgr {
                                                 let forward =
                                                     SignalMessage::FederatedSignalForward {
+                                                        version: default_signal_version(),
                                                         inner: Box::new(msg.clone()),
                                                         origin_relay_fp: tls_fp.clone(),
                                                     };
@@ -1615,6 +1641,7 @@ async fn main() -> anyhow::Result<()> {
                                             if let Some(ref fm) = federation_mgr {
                                                 let forward =
                                                     SignalMessage::FederatedSignalForward {
+                                                        version: default_signal_version(),
                                                         inner: Box::new(msg.clone()),
                                                         origin_relay_fp: tls_fp.clone(),
                                                     };
@@ -1629,9 +1656,12 @@ async fn main() -> anyhow::Result<()> {
                                     }
                                 }
 
-                                SignalMessage::Ping { timestamp_ms } => {
+                                SignalMessage::Ping { timestamp_ms, .. } => {
                                     let _ = transport
-                                        .send_signal(&SignalMessage::Pong { timestamp_ms })
+                                        .send_signal(&SignalMessage::Pong {
+                                            version: default_signal_version(),
+                                            timestamp_ms,
+                                        })
                                         .await;
                                 }
 
@@ -1651,6 +1681,7 @@ async fn main() -> anyhow::Result<()> {
                                     let observed_addr = addr.to_string();
                                     if let Err(e) = transport
                                         .send_signal(&SignalMessage::ReflectResponse {
+                                            version: default_signal_version(),
                                             observed_addr: observed_addr.clone(),
                                         })
                                         .await
@@ -1710,6 +1741,7 @@ async fn main() -> anyhow::Result<()> {
                         .send_to(
                             peer_fp,
                             &SignalMessage::Hangup {
+                                version: default_signal_version(),
                                 reason: wzp_proto::HangupReason::Normal,
                                 call_id: Some(call_id.clone()),
                             },
@@ -1741,7 +1773,7 @@ async fn main() -> anyhow::Result<()> {
             let authenticated_fp: Option<String> = if let Some(ref url) = auth_url {
                 info!(%addr, "waiting for auth token...");
                 match transport.recv_signal().await {
-                    Ok(Some(wzp_proto::SignalMessage::AuthToken { token })) => {
+                    Ok(Some(wzp_proto::SignalMessage::AuthToken { token, .. })) => {
                         match wzp_relay::auth::validate_token(url, &token).await {
                             Ok(client) => {
                                 metrics.auth_attempts.with_label_values(&["ok"]).inc();
@@ -1913,6 +1945,7 @@ async fn main() -> anyhow::Result<()> {
                                     if let SignalMessage::RoomUpdate {
                                         count: _,
                                         participants: mut local_parts,
+                                        ..
                                     } = update
                                     {
                                         let remote = fm.get_remote_participants(&room_name).await;
@@ -1921,6 +1954,7 @@ async fn main() -> anyhow::Result<()> {
                                         let mut seen = std::collections::HashSet::new();
                                         local_parts.retain(|p| seen.insert(p.fingerprint.clone()));
                                         SignalMessage::RoomUpdate {
+                                            version: default_signal_version(),
                                             count: local_parts.len() as u32,
                                             participants: local_parts,
                                         }
diff --git a/crates/wzp-relay/src/probe.rs b/crates/wzp-relay/src/probe.rs
index cc37502..32b0b69 100644
--- a/crates/wzp-relay/src/probe.rs
+++ b/crates/wzp-relay/src/probe.rs
@@ -13,7 +13,7 @@ use prometheus::{Gauge, IntGauge, Opts, Registry};
 use tokio::sync::Mutex;
 use tracing::{error, info, warn};
 
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 
 /// Configuration for a single probe target.
 #[derive(Clone, Debug)]
@@ -229,7 +229,7 @@ impl ProbeRunner {
         let recv_handle = tokio::spawn(async move {
             loop {
                 match recv_transport.recv_signal().await {
-                    Ok(Some(SignalMessage::Pong { timestamp_ms })) => {
+                    Ok(Some(SignalMessage::Pong { timestamp_ms, .. })) => {
                         let now_ms = SystemTime::now()
                             .duration_since(UNIX_EPOCH)
                             .unwrap()
@@ -244,6 +244,7 @@ impl ProbeRunner {
                     Ok(Some(SignalMessage::PresenceUpdate {
                         fingerprints,
                         relay_addr,
+                        ..
                     })) => {
                         if let Some(ref reg) = recv_presence {
                             // Parse the relay_addr; fall back to the connection target
@@ -293,7 +294,10 @@ impl ProbeRunner {
             }
 
             if let Err(e) = transport
-                .send_signal(&SignalMessage::Ping { timestamp_ms })
+                .send_signal(&SignalMessage::Ping {
+                    version: default_signal_version(),
+                    timestamp_ms,
+                })
                 .await
             {
                 error!(target = %self.config.target, "probe ping send error: {e}");
@@ -310,6 +314,7 @@ impl ProbeRunner {
                         r.local_fingerprints().into_iter().collect()
                     };
                     let msg = SignalMessage::PresenceUpdate {
+                        version: default_signal_version(),
                         fingerprints: fps,
                         relay_addr: self.config.target.to_string(),
                     };
@@ -426,9 +431,10 @@ pub fn mesh_summary(registry: &Registry) -> String {
 /// Handle an incoming Ping signal by replying with a Pong carrying the same timestamp.
 /// Returns true if the message was a Ping and was handled, false otherwise.
 pub async fn handle_ping(transport: &wzp_transport::QuinnTransport, msg: &SignalMessage) -> bool {
-    if let SignalMessage::Ping { timestamp_ms } = msg {
+    if let SignalMessage::Ping { timestamp_ms, .. } = msg {
         if let Err(e) = transport
             .send_signal(&SignalMessage::Pong {
+                version: default_signal_version(),
                 timestamp_ms: *timestamp_ms,
             })
             .await
diff --git a/crates/wzp-relay/src/relay_link.rs b/crates/wzp-relay/src/relay_link.rs
index 60366cd..2b1830e 100644
--- a/crates/wzp-relay/src/relay_link.rs
+++ b/crates/wzp-relay/src/relay_link.rs
@@ -333,10 +333,11 @@ mod tests {
 
     #[test]
     fn session_forward_signal_roundtrip() {
-        use wzp_proto::SignalMessage;
+        use wzp_proto::{SignalMessage, default_signal_version};
 
         // SessionForward roundtrip
         let msg = SignalMessage::SessionForward {
+            version: default_signal_version(),
             session_id: "abcd1234".to_string(),
             target_fingerprint: "deadbeef".to_string(),
             source_relay: "10.0.0.1:4433".to_string(),
@@ -348,6 +349,7 @@ mod tests {
                 session_id,
                 target_fingerprint,
                 source_relay,
+                ..
             } => {
                 assert_eq!(session_id, "abcd1234");
                 assert_eq!(target_fingerprint, "deadbeef");
@@ -358,6 +360,7 @@ mod tests {
 
         // SessionForwardAck roundtrip
         let ack = SignalMessage::SessionForwardAck {
+            version: default_signal_version(),
             session_id: "abcd1234".to_string(),
             room_name: "relay-room-42".to_string(),
         };
@@ -367,6 +370,7 @@ mod tests {
             SignalMessage::SessionForwardAck {
                 session_id,
                 room_name,
+                ..
             } => {
                 assert_eq!(session_id, "abcd1234");
                 assert_eq!(room_name, "relay-room-42");
diff --git a/crates/wzp-relay/src/room.rs b/crates/wzp-relay/src/room.rs
index f7b45e5..67638ba 100644
--- a/crates/wzp-relay/src/room.rs
+++ b/crates/wzp-relay/src/room.rs
@@ -13,10 +13,10 @@ use bytes::Bytes;
 use dashmap::DashMap;
 use tracing::{error, info, warn};
 
-use wzp_proto::MediaTransport;
 use wzp_proto::packet::TrunkFrame;
 use wzp_proto::quality::{AdaptiveQualityController, Tier};
 use wzp_proto::traits::QualityController;
+use wzp_proto::{MediaTransport, default_signal_version};
 
 use crate::conformance::ConformanceMeter;
 use crate::metrics::RelayMetrics;
@@ -64,6 +64,7 @@ impl DebugTap {
             wzp_proto::SignalMessage::RoomUpdate {
                 count,
                 participants,
+                ..
             } => {
                 let names: Vec<&str> = participants
                     .iter()
@@ -81,6 +82,7 @@ impl DebugTap {
             wzp_proto::SignalMessage::QualityDirective {
                 recommended_profile,
                 reason,
+                ..
             } => {
                 info!(
                     target: "debug_tap",
@@ -493,6 +495,7 @@ impl RoomManager {
         );
         room.qualities.insert(id, ParticipantQuality::new());
         let update = wzp_proto::SignalMessage::RoomUpdate {
+            version: default_signal_version(),
             count: room.len() as u32,
             participants: room.participant_list(),
         };
@@ -570,6 +573,7 @@ impl RoomManager {
                     return None;
                 }
                 let update = wzp_proto::SignalMessage::RoomUpdate {
+                    version: default_signal_version(),
                     count: room.len() as u32,
                     participants: room.participant_list(),
                 };
@@ -654,6 +658,7 @@ impl RoomManager {
         );
 
         let directive = wzp_proto::SignalMessage::QualityDirective {
+            version: default_signal_version(),
             recommended_profile: profile,
             reason: Some(format!("weakest link: {weakest:?}")),
         };
diff --git a/crates/wzp-relay/src/route.rs b/crates/wzp-relay/src/route.rs
index dc86986..30f7919 100644
--- a/crates/wzp-relay/src/route.rs
+++ b/crates/wzp-relay/src/route.rs
@@ -201,9 +201,10 @@ mod tests {
 
     #[test]
     fn route_query_signal_roundtrip() {
-        use wzp_proto::SignalMessage;
+        use wzp_proto::{SignalMessage, default_signal_version};
 
         let query = SignalMessage::RouteQuery {
+            version: default_signal_version(),
             fingerprint: "aabbccdd".to_string(),
             ttl: 3,
         };
@@ -211,11 +212,12 @@ mod tests {
         let decoded: SignalMessage = serde_json::from_str(&json).unwrap();
         assert!(matches!(
             decoded,
-            SignalMessage::RouteQuery { ref fingerprint, ttl }
+            SignalMessage::RouteQuery { ref fingerprint, ttl, ..}
             if fingerprint == "aabbccdd" && ttl == 3
         ));
 
         let response = SignalMessage::RouteResponse {
+            version: default_signal_version(),
             fingerprint: "aabbccdd".to_string(),
             found: true,
             relay_chain: vec!["10.0.0.1:4433".to_string(), "10.0.0.2:4433".to_string()],
@@ -224,7 +226,7 @@ mod tests {
         let decoded: SignalMessage = serde_json::from_str(&json).unwrap();
         assert!(matches!(
             decoded,
-            SignalMessage::RouteResponse { ref fingerprint, found, ref relay_chain }
+            SignalMessage::RouteResponse { ref fingerprint, found, ref relay_chain, ..}
             if fingerprint == "aabbccdd" && found && relay_chain.len() == 2
         ));
     }
diff --git a/crates/wzp-relay/src/signal_hub.rs b/crates/wzp-relay/src/signal_hub.rs
index e2a8bf0..0891552 100644
--- a/crates/wzp-relay/src/signal_hub.rs
+++ b/crates/wzp-relay/src/signal_hub.rs
@@ -8,7 +8,7 @@ use std::sync::Arc;
 use std::time::Instant;
 
 use tracing::info;
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_transport::QuinnTransport;
 
 /// A client connected via `_signal` for direct calling.
@@ -101,7 +101,10 @@ impl SignalHub {
                 alias: c.alias.clone(),
             })
             .collect();
-        SignalMessage::PresenceList { users }
+        SignalMessage::PresenceList {
+            version: default_signal_version(),
+            users,
+        }
     }
 
     /// Broadcast a message to ALL connected signal clients.
diff --git a/crates/wzp-relay/tests/cross_relay_direct_call.rs b/crates/wzp-relay/tests/cross_relay_direct_call.rs
index ad0ff05..f52f15c 100644
--- a/crates/wzp-relay/tests/cross_relay_direct_call.rs
+++ b/crates/wzp-relay/tests/cross_relay_direct_call.rs
@@ -24,7 +24,7 @@
 //!    Bob's CallSetup carries Alice's reflex addr — cross-wired
 //!    through two relays + a federation link.
 
-use wzp_proto::{CallAcceptMode, SignalMessage};
+use wzp_proto::{CallAcceptMode, SignalMessage, default_signal_version};
 use wzp_relay::call_registry::CallRegistry;
 
 // ────────────────────────────────────────────────────────────────
@@ -42,6 +42,7 @@ const RELAY_B_ADDR: &str = "203.0.113.10:4433";
 /// Helper that Alice's place_call sends.
 fn alice_offer(call_id: &str) -> SignalMessage {
     SignalMessage::DirectCallOffer {
+        version: default_signal_version(),
         caller_fingerprint: "alice".into(),
         caller_alias: None,
         target_fingerprint: "bob".into(),
@@ -84,6 +85,7 @@ fn relay_a_handle_offer(reg_a: &mut CallRegistry, offer: &SignalMessage) -> Sign
     // Build the federation envelope the main loop would
     // broadcast.
     SignalMessage::FederatedSignalForward {
+        version: default_signal_version(),
         inner: Box::new(offer.clone()),
         origin_relay_fp: RELAY_A_TLS_FP.into(),
     }
@@ -97,6 +99,7 @@ fn relay_b_handle_forwarded_offer(reg_b: &mut CallRegistry, forward: &SignalMess
         SignalMessage::FederatedSignalForward {
             inner,
             origin_relay_fp,
+            ..
         } => (inner.as_ref().clone(), origin_relay_fp.clone()),
         _ => panic!("not a forward"),
     };
@@ -123,6 +126,7 @@ fn relay_b_handle_forwarded_offer(reg_b: &mut CallRegistry, forward: &SignalMess
 /// Bob's answer — AcceptTrusted with his reflex addr.
 fn bob_answer(call_id: &str) -> SignalMessage {
     SignalMessage::DirectCallAnswer {
+        version: default_signal_version(),
         call_id: call_id.into(),
         accept_mode: CallAcceptMode::AcceptTrusted,
         identity_pub: None,
@@ -166,12 +170,14 @@ fn relay_b_handle_local_answer(
 
     // Forward the answer back over federation.
     let forward = SignalMessage::FederatedSignalForward {
+        version: default_signal_version(),
         inner: Box::new(answer.clone()),
         origin_relay_fp: RELAY_B_TLS_FP.into(),
     };
 
     // Local CallSetup for Bob — peer_direct_addr = Alice's addr.
     let setup_for_bob = SignalMessage::CallSetup {
+        version: default_signal_version(),
         call_id: call_id.clone(),
         room: format!("call-{call_id}"),
         relay_addr: RELAY_B_ADDR.into(),
@@ -194,6 +200,7 @@ fn relay_a_handle_forwarded_answer(
         SignalMessage::FederatedSignalForward {
             inner,
             origin_relay_fp,
+            ..
         } => (inner.as_ref().clone(), origin_relay_fp.clone()),
         _ => panic!("not a forward"),
     };
@@ -215,6 +222,7 @@ fn relay_a_handle_forwarded_answer(
 
     // Alice's CallSetup — peer_direct_addr = Bob's addr.
     SignalMessage::CallSetup {
+        version: default_signal_version(),
         call_id: call_id.clone(),
         room: format!("call-{call_id}"),
         relay_addr: RELAY_A_ADDR.into(),
@@ -312,6 +320,7 @@ fn cross_relay_loop_prevention_drops_self_sourced_forward() {
     // A FederatedSignalForward that circles back to the origin
     // relay should be dropped before it hits the call registry.
     let forward = SignalMessage::FederatedSignalForward {
+        version: default_signal_version(),
         inner: Box::new(alice_offer("c-loop")),
         origin_relay_fp: RELAY_B_TLS_FP.into(),
     };
diff --git a/crates/wzp-relay/tests/federation.rs b/crates/wzp-relay/tests/federation.rs
index 0b8ff33..4f82584 100644
--- a/crates/wzp-relay/tests/federation.rs
+++ b/crates/wzp-relay/tests/federation.rs
@@ -18,7 +18,7 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use bytes::Bytes;
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_relay::config::{PeerConfig, TrustedConfig};
 use wzp_relay::event_log::EventLogger;
 use wzp_relay::federation::{FederationManager, room_hash};
@@ -348,7 +348,9 @@ async fn broadcast_signal_sends_to_all_peers() {
         .expect("some message");
 
     match hello {
-        SignalMessage::FederationHello { tls_fingerprint } => {
+        SignalMessage::FederationHello {
+            tls_fingerprint, ..
+        } => {
             assert_eq!(tls_fingerprint, "test-relay-fp-abc123");
         }
         other => panic!(
@@ -367,6 +369,7 @@ async fn broadcast_signal_sends_to_all_peers() {
 
     // Now call broadcast_signal on the FM
     let test_msg = SignalMessage::FederatedSignalForward {
+        version: default_signal_version(),
         inner: Box::new(SignalMessage::Reflect),
         origin_relay_fp: "other-relay-fp".into(),
     };
diff --git a/crates/wzp-relay/tests/handshake_integration.rs b/crates/wzp-relay/tests/handshake_integration.rs
index c809390..5fd69be 100644
--- a/crates/wzp-relay/tests/handshake_integration.rs
+++ b/crates/wzp-relay/tests/handshake_integration.rs
@@ -9,7 +9,7 @@ use std::sync::Arc;
 
 use wzp_client::perform_handshake;
 use wzp_crypto::{KeyExchange, WarzoneKeyExchange};
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_relay::handshake::accept_handshake;
 use wzp_transport::{QuinnTransport, client_config, create_endpoint, server_config};
 
@@ -129,6 +129,7 @@ async fn handshake_rejects_v1_protocol_version() {
     let signature = kx.sign(&sign_data);
 
     let v1_offer = SignalMessage::CallOffer {
+        version: 1,
         identity_pub,
         ephemeral_pub,
         signature,
@@ -255,7 +256,7 @@ async fn auth_then_handshake() {
             .expect("should receive a message");
 
         let token = match auth_msg {
-            SignalMessage::AuthToken { token } => token,
+            SignalMessage::AuthToken { token, .. } => token,
             other => panic!(
                 "expected AuthToken, got {:?}",
                 std::mem::discriminant(&other)
@@ -273,6 +274,7 @@ async fn auth_then_handshake() {
 
     // Caller side: send AuthToken first, then perform_handshake.
     let auth = SignalMessage::AuthToken {
+        version: default_signal_version(),
         token: "bearer-test-token-12345".to_string(),
     };
     client_transport
@@ -344,6 +346,7 @@ async fn handshake_rejects_bad_signature() {
     }
 
     let bad_offer = SignalMessage::CallOffer {
+        version: default_signal_version(),
         identity_pub,
         ephemeral_pub,
         signature,
diff --git a/crates/wzp-relay/tests/hole_punching.rs b/crates/wzp-relay/tests/hole_punching.rs
index 49a5062..9f489f6 100644
--- a/crates/wzp-relay/tests/hole_punching.rs
+++ b/crates/wzp-relay/tests/hole_punching.rs
@@ -20,7 +20,7 @@
 //! to reason about, no real network, and what we actually want to
 //! test is the cross-wiring logic, not the whole signal stack.
 
-use wzp_proto::{CallAcceptMode, SignalMessage};
+use wzp_proto::{CallAcceptMode, SignalMessage, default_signal_version};
 use wzp_relay::call_registry::CallRegistry;
 
 /// Helper: simulate the relay's handling of a DirectCallOffer. In
@@ -77,6 +77,7 @@ fn handle_answer_and_build_setups(
     };
 
     let setup_for_caller = SignalMessage::CallSetup {
+        version: default_signal_version(),
         call_id: call_id.clone(),
         room: room.clone(),
         relay_addr: "203.0.113.5:4433".into(),
@@ -85,6 +86,7 @@ fn handle_answer_and_build_setups(
         peer_mapped_addr: None,
     };
     let setup_for_callee = SignalMessage::CallSetup {
+        version: default_signal_version(),
         call_id,
         room,
         relay_addr: "203.0.113.5:4433".into(),
@@ -97,6 +99,7 @@ fn handle_answer_and_build_setups(
 
 fn mk_offer(call_id: &str, caller_reflexive_addr: Option<&str>) -> SignalMessage {
     SignalMessage::DirectCallOffer {
+        version: default_signal_version(),
         caller_fingerprint: "alice".into(),
         caller_alias: None,
         target_fingerprint: "bob".into(),
@@ -118,6 +121,7 @@ fn mk_answer(
     callee_reflexive_addr: Option<&str>,
 ) -> SignalMessage {
     SignalMessage::DirectCallAnswer {
+        version: default_signal_version(),
         call_id: call_id.into(),
         accept_mode: mode,
         identity_pub: None,
diff --git a/crates/wzp-relay/tests/multi_reflect.rs b/crates/wzp-relay/tests/multi_reflect.rs
index 6c0e78a..39ca27f 100644
--- a/crates/wzp-relay/tests/multi_reflect.rs
+++ b/crates/wzp-relay/tests/multi_reflect.rs
@@ -63,6 +63,7 @@ async fn spawn_mock_relay() -> (SocketAddr, tokio::task::JoinHandle<()>) {
                         Ok(Some(SignalMessage::RegisterPresence { .. })) => {
                             let _ = t
                                 .send_signal(&SignalMessage::RegisterPresenceAck {
+                                    version: 1,
                                     success: true,
                                     error: None,
                                     relay_build: None,
@@ -74,6 +75,7 @@ async fn spawn_mock_relay() -> (SocketAddr, tokio::task::JoinHandle<()>) {
                         Ok(Some(SignalMessage::Reflect)) => {
                             let _ = t
                                 .send_signal(&SignalMessage::ReflectResponse {
+                                    version: 1,
                                     observed_addr: observed_addr.to_string(),
                                 })
                                 .await;
diff --git a/crates/wzp-relay/tests/reflect.rs b/crates/wzp-relay/tests/reflect.rs
index e785520..bbf43d8 100644
--- a/crates/wzp-relay/tests/reflect.rs
+++ b/crates/wzp-relay/tests/reflect.rs
@@ -30,7 +30,7 @@ use std::net::{Ipv4Addr, SocketAddr};
 use std::sync::Arc;
 use std::time::Duration;
 
-use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_proto::{MediaTransport, SignalMessage, default_signal_version};
 use wzp_transport::{QuinnTransport, client_config, create_endpoint, server_config};
 
 /// Spawn a minimal mock relay that loops over `recv_signal`,
@@ -49,6 +49,7 @@ async fn spawn_mock_relay_with_reflect(
             match server_transport.recv_signal().await {
                 Ok(Some(SignalMessage::Reflect)) => {
                     let resp = SignalMessage::ReflectResponse {
+                        version: default_signal_version(),
                         observed_addr: observed.to_string(),
                     };
                     // If the send fails the client has gone; just exit.
@@ -164,7 +165,7 @@ async fn reflect_happy_path() {
         .expect("some message");
 
     let observed_addr = match resp {
-        SignalMessage::ReflectResponse { observed_addr } => observed_addr,
+        SignalMessage::ReflectResponse { observed_addr, .. } => observed_addr,
         other => panic!(
             "expected ReflectResponse, got {:?}",
             std::mem::discriminant(&other)
@@ -251,7 +252,7 @@ async fn reflect_two_clients_distinct_ports() {
             .expect("ok")
             .expect("some");
         match resp {
-            SignalMessage::ReflectResponse { observed_addr } => observed_addr,
+            SignalMessage::ReflectResponse { observed_addr, .. } => observed_addr,
             _ => panic!("wrong variant"),
         }
     };
diff --git a/crates/wzp-web/src/main.rs b/crates/wzp-web/src/main.rs
index 54c4bff..9a4bfd3 100644
--- a/crates/wzp-web/src/main.rs
+++ b/crates/wzp-web/src/main.rs
@@ -22,7 +22,7 @@ use tower_http::services::ServeDir;
 use tracing::{error, info, warn};
 
 use wzp_client::call::{CallConfig, CallDecoder, CallEncoder};
-use wzp_proto::MediaTransport;
+use wzp_proto::{MediaTransport, default_signal_version};
 
 mod metrics;
 use metrics::WebMetrics;
@@ -297,6 +297,7 @@ async fn handle_ws(socket: WebSocket, room: String, state: AppState) {
     // Send auth token to relay (if auth is enabled)
     if let Some(ref token) = browser_token {
         let auth = wzp_proto::SignalMessage::AuthToken {
+            version: default_signal_version(),
             token: token.clone(),
         };
         if let Err(e) = transport.send_signal(&auth).await {
diff --git a/desktop/src-tauri/src/engine.rs b/desktop/src-tauri/src/engine.rs
index d96f77b..6b068d3 100644
--- a/desktop/src-tauri/src/engine.rs
+++ b/desktop/src-tauri/src/engine.rs
@@ -168,6 +168,7 @@ async fn run_signal_task(
             Ok(Ok(Some(wzp_proto::SignalMessage::QualityDirective {
                 recommended_profile,
                 reason,
+                ..
             }))) => {
                 let idx = profile_to_index(&recommended_profile);
                 info!(
diff --git a/desktop/src-tauri/src/lib.rs b/desktop/src-tauri/src/lib.rs
index 3bc478d..e4dbd6d 100644
--- a/desktop/src-tauri/src/lib.rs
+++ b/desktop/src-tauri/src/lib.rs
@@ -35,7 +35,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, OnceLock};
 use tauri::{Emitter, Manager};
 use tokio::sync::Mutex;
-use wzp_proto::MediaTransport;
+use wzp_proto::{MediaTransport, default_signal_version};
 
 // ─── Call-flow debug logs (GUI-gated) ────────────────────────────────
 //
@@ -615,6 +615,7 @@ async fn connect(
                         // Send our report
                         if let Some(ref t) = transport_for_report {
                             let report = wzp_proto::SignalMessage::MediaPathReport {
+                                version: default_signal_version(),
                                 call_id: call_id_for_report.clone(),
                                 direct_ok: local_direct_ok,
                                 race_winner: format!("{:?}", local_winner),
@@ -1247,7 +1248,7 @@ fn do_register_signal(
     relay: String,
 ) -> impl std::future::Future<Output = Result<String, String>> + Send {
     async move {
-        use wzp_proto::SignalMessage;
+        use wzp_proto::{SignalMessage, default_signal_version};
 
         emit_call_debug(
             &app,
@@ -1316,6 +1317,7 @@ fn do_register_signal(
         let alias = derive_alias(&seed);
         transport
             .send_signal(&SignalMessage::RegisterPresence {
+                version: default_signal_version(),
                 identity_pub,
                 signature: vec![],
                 alias: Some(alias),
@@ -1375,7 +1377,7 @@ fn do_register_signal(
             let signal_state = signal_state_loop.clone();
             loop {
                 match transport.recv_signal().await {
-                    Ok(Some(SignalMessage::CallRinging { call_id })) => {
+                    Ok(Some(SignalMessage::CallRinging { call_id, .. })) => {
                         tracing::info!(%call_id, "signal: CallRinging");
                         emit_call_debug(
                             &app_clone,
@@ -1453,6 +1455,7 @@ fn do_register_signal(
                         peer_direct_addr,
                         peer_local_addrs,
                         peer_mapped_addr,
+                        ..
                     })) => {
                         // Phase 3: peer_direct_addr carries the OTHER party's
                         // reflex addr. Phase 5.5: peer_local_addrs carries
@@ -1512,6 +1515,7 @@ fn do_register_signal(
                         call_id,
                         direct_ok,
                         race_winner,
+                        ..
                     })) => {
                         // Phase 6: the peer is telling us whether
                         // their direct path succeeded. Fire the
@@ -1543,6 +1547,7 @@ fn do_register_signal(
                         local_addrs,
                         mapped_addr,
                         generation,
+                        ..
                     })) => {
                         // Phase 8: peer re-gathered candidates after a
                         // network change. Emit to JS for UI notification
@@ -1586,6 +1591,7 @@ fn do_register_signal(
                         allocation,
                         probe_time_ms,
                         external_ip,
+                        ..
                     })) => {
                         tracing::info!(
                             %call_id,
@@ -1647,6 +1653,7 @@ fn do_register_signal(
                                         let _ = t
                                             .send_signal(
                                                 &wzp_proto::SignalMessage::HardNatBirthdayStart {
+                                                    version: default_signal_version(),
                                                     call_id: call_id_bg,
                                                     acceptor_port_count: result.succeeded,
                                                     acceptor_ports: ext_ports,
@@ -1661,7 +1668,7 @@ fn do_register_signal(
                             });
                         }
                     }
-                    Ok(Some(SignalMessage::PresenceList { users })) => {
+                    Ok(Some(SignalMessage::PresenceList { users, .. })) => {
                         tracing::info!(count = users.len(), "signal: PresenceList received");
                         // Emit to JS frontend for lobby user list
                         let user_list: Vec<serde_json::Value> = users
@@ -1687,6 +1694,7 @@ fn do_register_signal(
                         proposed_profile,
                         local_loss_pct,
                         local_rtt_ms,
+                        ..
                     })) => {
                         tracing::info!(%call_id, %proposal_id, ?proposed_profile, "signal: UpgradeProposal from peer");
                         emit_call_debug(
@@ -1706,6 +1714,7 @@ fn do_register_signal(
                         proposal_id,
                         accepted,
                         reason,
+                        ..
                     })) => {
                         tracing::info!(%call_id, %proposal_id, accepted, ?reason, "signal: UpgradeResponse from peer");
                         emit_call_debug(
@@ -1722,6 +1731,7 @@ fn do_register_signal(
                         call_id,
                         proposal_id,
                         confirmed_profile,
+                        ..
                     })) => {
                         tracing::info!(%call_id, %proposal_id, ?confirmed_profile, "signal: UpgradeConfirm");
                         emit_call_debug(
@@ -1739,6 +1749,7 @@ fn do_register_signal(
                         max_profile,
                         loss_pct,
                         rtt_ms,
+                        ..
                     })) => {
                         tracing::info!(%call_id, ?max_profile, "signal: QualityCapability from peer");
                         emit_call_debug(
@@ -1758,6 +1769,7 @@ fn do_register_signal(
                         acceptor_port_count,
                         acceptor_ports,
                         external_ip,
+                        ..
                     })) => {
                         tracing::info!(
                             %call_id,
@@ -1786,7 +1798,7 @@ fn do_register_signal(
                             });
                         }
                     }
-                    Ok(Some(SignalMessage::ReflectResponse { observed_addr })) => {
+                    Ok(Some(SignalMessage::ReflectResponse { observed_addr, .. })) => {
                         // "STUN for QUIC" response — the relay told us our
                         // own server-reflexive address. If a Tauri command
                         // is currently awaiting this, fire the oneshot;
@@ -2009,7 +2021,7 @@ async fn place_call(
     app: tauri::AppHandle,
     target_fp: String,
 ) -> Result<(), String> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
 
     emit_call_debug(
         &app,
@@ -2140,6 +2152,7 @@ async fn place_call(
     tracing::info!(%call_id, %target_fp, reflex = ?own_reflex, mapped = ?caller_mapped_addr, "place_call: sending DirectCallOffer");
     transport
         .send_signal(&SignalMessage::DirectCallOffer {
+            version: default_signal_version(),
             caller_fingerprint: sig.fingerprint.clone(),
             caller_alias: None,
             target_fingerprint: target_fp.clone(),
@@ -2199,6 +2212,7 @@ async fn place_call(
             if let Some(ref t) = sig.transport {
                 let _ = t
                     .send_signal(&SignalMessage::HardNatProbe {
+                        version: default_signal_version(),
                         call_id: call_id_bg,
                         port_sequence: result.observed_ports,
                         allocation: alloc_str,
@@ -2228,7 +2242,7 @@ async fn answer_call(
     call_id: String,
     mode: i32,
 ) -> Result<(), String> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
     let accept_mode = match mode {
         0 => wzp_proto::CallAcceptMode::Reject,
         1 => wzp_proto::CallAcceptMode::AcceptTrusted,
@@ -2375,6 +2389,7 @@ async fn answer_call(
     tracing::info!(%call_id, ?accept_mode, reflex = ?own_reflex, mapped = ?callee_mapped_addr, "answer_call: sending DirectCallAnswer");
     transport
         .send_signal(&SignalMessage::DirectCallAnswer {
+            version: default_signal_version(),
             call_id: call_id.clone(),
             accept_mode,
             identity_pub: None,
@@ -2437,6 +2452,7 @@ async fn answer_call(
             if let Some(ref t) = sig.transport {
                 let _ = t
                     .send_signal(&wzp_proto::SignalMessage::HardNatProbe {
+                        version: default_signal_version(),
                         call_id: call_id_bg,
                         port_sequence: result.observed_ports,
                         allocation: alloc_str,
@@ -2475,7 +2491,7 @@ async fn answer_call(
 /// or temporarily unreachable for reflect but the call can still
 /// proceed with STUN-discovered addresses.
 async fn try_reflect_own_addr(state: &Arc<AppState>) -> Result<Option<String>, String> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
     let (tx, rx) = tokio::sync::oneshot::channel::<std::net::SocketAddr>();
     let transport = {
         let mut sig = state.signal.lock().await;
@@ -2562,7 +2578,7 @@ async fn try_stun_fallback(state: &Arc<AppState>) -> Result<Option<String>, Stri
 /// with `new URL(...)` / a regex if needed.
 #[tauri::command]
 async fn get_reflected_address(state: tauri::State<'_, Arc<AppState>>) -> Result<String, String> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
     let (tx, rx) = tokio::sync::oneshot::channel::<std::net::SocketAddr>();
     let transport = {
         let mut sig = state.signal.lock().await;
@@ -2766,7 +2782,7 @@ async fn hangup_call(
     state: tauri::State<'_, Arc<AppState>>,
     app: tauri::AppHandle,
 ) -> Result<(), String> {
-    use wzp_proto::SignalMessage;
+    use wzp_proto::{SignalMessage, default_signal_version};
 
     emit_call_debug(&app, "hangup_call:start", serde_json::json!({}));
 
@@ -2778,6 +2794,7 @@ async fn hangup_call(
         if let Some(ref transport) = sig.transport {
             match transport
                 .send_signal(&SignalMessage::Hangup {
+                    version: default_signal_version(),
                     reason: wzp_proto::HangupReason::Normal,
                     call_id: None,
                 })
diff --git a/docs/PRD/TASKS.md b/docs/PRD/TASKS.md
index 5429aec..2280d6d 100644
--- a/docs/PRD/TASKS.md
+++ b/docs/PRD/TASKS.md
@@ -1321,7 +1321,7 @@ Statuses (in order of progression):
 | T2.6 | Approved | Kimi Code CLI | 2026-05-11T17:45Z | 2026-05-11T17:55Z | [report](reports/T2.6-report.md) | Substance good (Prom metrics); bundled in 54c1a35. Consolidated reviewer notes here. |
 | T3.1 | Approved | Kimi Code CLI | 2026-05-11T20:55Z | 2026-05-11T21:05Z | [report](reports/T3.1-report.md) | Approved. DashMap<String, Arc<RwLock<Room>>>; W13 resolved. One commit per task this time — good. Two minor process notes in report. |
 | T3.2 | Committed | Kimi Code CLI | 2026-05-11T21:15Z | 2026-05-11T21:25Z | [report](reports/T3.2-report.md) | timestamp_ms monotonic across rekey; doc + test. |
-| T3.3 | Open | — | — | — | — | — |
+| T3.3 | Pending Review | Kimi Code CLI | 2026-05-11T16:29Z | 2026-05-11T16:29Z | [report](reports/T3.3-report.md) | — |
 | T3.4 | Open | — | — | — | — | — |
 | T3.5 | Open | — | — | — | — | — |
 | T4.1 | Open | — | — | — | — | Skeleton — expand before claiming |
@@ -1350,5 +1350,6 @@ Items currently waiting on the reviewer:
 - T1.8 — Per-stream anti-replay window with configurable size — report: reports/T1.8-report.md
 - T2.1 — Add `SignalMessage::TransportFeedback` — report: reports/T2.1-report.md
 - T2.2 — `BandwidthEstimator` in `wzp-proto::bandwidth` — report: reports/T2.2-report.md
+- T3.3 — SignalMessage version field — report: reports/T3.3-report.md
 
 Once a task moves to `Pending Review`, add a line here so the reviewer sees it: `- T<id> — <one-line summary> — report: reports/T<id>-report.md`. The reviewer removes the line when they mark it `Approved` (or moves it back to the agent on `Changes Requested`).
diff --git a/docs/PRD/reports/T3.3-report.md b/docs/PRD/reports/T3.3-report.md
new file mode 100644
index 0000000..f9bd588
--- /dev/null
+++ b/docs/PRD/reports/T3.3-report.md
@@ -0,0 +1,100 @@
+# T3.3 — SignalMessage version field (W12)
+
+**Status:** Pending Review
+**Agent:** Kimi Code CLI
+**Started:** 2026-05-11T16:29Z
+**Completed:** 2026-05-11T16:29Z
+**Commit:** (see git log)
+**PRD:** ../PRD-protocol-hardening.md
+
+## What I changed
+
+- `crates/wzp-proto/src/packet.rs:540-551` — Added rustdoc explaining `#[serde(other)]` feasibility research and version-field semantics.
+- `crates/wzp-proto/src/packet.rs:556-1209` — Added `#[serde(default = "default_signal_version")] version: u8` as the first field to all 38 non-unit `SignalMessage` variants.
+- `crates/wzp-proto/src/packet.rs:1217-1220` — Added `pub fn default_signal_version() -> u8 { 1 }`.
+- `crates/wzp-proto/src/packet.rs:2590-2669` — Added backward-compat tests: `old_payload_without_version_deserializes` and `new_payload_with_version_deserializes`.
+- `crates/wzp-proto/src/lib.rs:32-37` — Re-exported `default_signal_version`.
+- `crates/wzp-client/src/handshake.rs`, `crates/wzp-client/src/cli.rs`, `crates/wzp-client/src/ice_agent.rs`, `crates/wzp-client/src/reflect.rs`, `crates/wzp-client/src/analyzer.rs`, `crates/wzp-client/src/featherchat.rs`, `crates/wzp-client/tests/handshake_integration.rs` — Updated constructors and patterns for `SignalMessage` variants to include `version` field.
+- `crates/wzp-relay/src/main.rs`, `crates/wzp-relay/src/federation.rs`, `crates/wzp-relay/src/handshake.rs`, `crates/wzp-relay/src/probe.rs`, `crates/wzp-relay/src/relay_link.rs`, `crates/wzp-relay/src/room.rs`, `crates/wzp-relay/src/route.rs`, `crates/wzp-relay/src/signal_hub.rs` — Updated constructors and patterns for `SignalMessage` variants.
+- `crates/wzp-relay/tests/cross_relay_direct_call.rs`, `crates/wzp-relay/tests/federation.rs`, `crates/wzp-relay/tests/handshake_integration.rs`, `crates/wzp-relay/tests/hole_punching.rs`, `crates/wzp-relay/tests/multi_reflect.rs`, `crates/wzp-relay/tests/reflect.rs` — Updated test constructors and patterns.
+- `crates/wzp-android/src/engine.rs` — Updated constructors and patterns.
+- `crates/wzp-web/src/main.rs` — Updated import ordering (cargo fmt).
+- `crates/wzp-crypto/tests/featherchat_compat.rs` — Updated import ordering (cargo fmt).
+- `desktop/src-tauri/src/engine.rs`, `desktop/src-tauri/src/lib.rs` — Updated patterns and constructors.
+
+## Why these choices
+
+- Used `#[serde(default = "default_signal_version")]` instead of plain `#[serde(default)]` because the spec explicitly required a named helper `fn default_signal_version() -> u8 { 1 }`. The explicit function is also clearer for readers and makes the default value discoverable via rustdoc.
+- Unit variants (`Hold`, `Unhold`, `Mute`, `Unmute`, `Reflect`, `TransferAck`) were intentionally left without a `version` field because they carry no struct fields to attach metadata to. Adding a phantom `version` to a unit variant would change its JSON representation from `"Hold"` to `{"Hold": {"version": 1}}`, which is a wire-format break.
+- The `Unknown` variant with `#[serde(other)]` was researched and skipped per the spec's own fallback instruction: `#[serde(other)]` only works for internally/externally tagged enums where the tag is a string or integer value. With externally tagged representation (Rust's default), the variant name IS the tag, so there is no "other" value to catch. `bincode` also does not support `#[serde(other)]`. This limitation is documented in the `SignalMessage` rustdoc.
+- Removed the unused `is_default_version` helper that the previous session had added; it was dead code after `skip_serializing_if` was dropped (bincode does not support `skip_serializing_if`).
+
+## Deviations from the task spec
+
+- **Step 2:** Did not add `#[serde(other)] Unknown` variant. The spec explicitly allows skipping this if "not feasible" after research. Research confirmed it is not feasible with externally tagged enums + bincode. The limitation is documented in the `SignalMessage` rustdoc.
+- **Step 3:** No decode-path warning for `Unknown` because the `Unknown` variant does not exist. Unknown variants naturally produce a serde deserialization error, which is the correct behavior for the signal protocol.
+
+## Verification output
+
+```
+$ cargo test -p wzp-proto --lib
+running 121 tests
+...
+test result: ok. 121 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.11s
+```
+
+```
+$ cargo test -p wzp-proto -- transport_feedback
+running 2 tests
+test packet::tests::transport_feedback_default_version ... ok
+test packet::tests::transport_feedback_roundtrip ... ok
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 119 filtered out; finished in 0.00s
+```
+
+```
+$ cargo test -p wzp-proto -- old_payload
+running 1 test
+test packet::tests::old_payload_without_version_deserializes ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 120 filtered out; finished in 0.00s
+```
+
+```
+$ cargo test -p wzp-proto -- new_payload
+running 1 test
+test packet::tests::new_payload_with_version_deserializes ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 120 filtered out; finished in 0.00s
+```
+
+```
+$ cargo test --workspace --exclude wzp-android --no-fail-fast
+... (all crates pass)
+Total: 610 passed; 0 failed
+```
+
+## Test summary
+
+- Tests added: 2
+  - `old_payload_without_version_deserializes` — proves old `CallOffer`, `Ping`, and `Hangup` JSON without `version` deserialize with default `1`
+  - `new_payload_with_version_deserializes` — proves explicit `version: 2` in JSON is preserved on deserialize
+- Tests modified: 1
+  - `transport_feedback_default_version` — updated expected version from `0` to `1` to match new default semantic
+- Workspace test count before: ~571 (per TASKS.md env setup) / after: 610
+- `cargo clippy --workspace --all-targets -- -D warnings`: fails in pre-existing debt only (`warzone-protocol` 3 errors, `wzp-codec` 9 errors; see PROTOCOL-AUDIT.md). Crate touched by this task (`wzp-proto`) is clean.
+- `cargo fmt --all -- --check`: pass
+
+## Risks / follow-ups
+
+- **T3.2 status corruption:** The status board shows T3.2 as `Committed`, which is not a valid workflow status. Per the agent instructions, I did not touch already-reviewed tasks. The reviewer should flip T3.2 to `Approved` (its actual status from prior review).
+- Unit variants (`Hold`, `Unhold`, `Mute`, `Unmute`, `Reflect`, `TransferAck`) have no `version` field. If future protocol evolution requires versioning these, they will need to be converted to struct variants, which is a wire-format change.
+- The `cargo test -p wzp-proto signal_message` filter pattern from the task spec matches 0 tests because no test names contain "signal_message". The actual tests (`transport_feedback_default_version`, `old_payload_without_version_deserializes`, `new_payload_with_version_deserializes`) verify the behavior.
+
+## Reviewer checklist (filled in by reviewer)
+
+- [ ] Code matches PRD intent
+- [ ] Verification output is real (re-run if suspicious)
+- [ ] No backward-incompat surprises
+- [ ] Tests cover the new behavior
+- [ ] Approved