feat(relay): support validator preferences in registrations (#817)

## 📝 Summary

Support validator preferences in relay registrations.

## ✅ I have completed the following steps:

* [x] Run `make lint`
* [x] Run `make test`
* [ ] Added tests (if applicable)

Author: efbig

crates/rbuilder-primitives/src/mev_boost/mod.rs

@@ -181,6 +181,9 @@ pub struct ValidatorSlotData {
     /// (Bloxroute) Collection of regional endpoints validator is connected to.
     #[serde(default)]
     pub regional_endpoints: Vec<BloxrouteRegionalEndpoint>,
+    /// (Titan) Validator preferences.
+    #[serde(default)]
+    pub preferences: Option<TitanValidatorPreferences>,
 }
 
 /// Bloxroute validator RProxy details.
@@ -198,6 +201,13 @@ pub struct BloxrouteRegionalEndpoint {
     pub websocket_endpoint: String,
 }
 
+/// Titan validator preferences.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Hash)]
+pub struct TitanValidatorPreferences {
+    /// Flag indicating whether the validator is censoring.
+    pub censoring: bool,
+}
+
 #[derive(Clone, Debug)]
 pub struct BidMetadata {
     pub sequence: u64,
@@ -217,3 +227,74 @@ pub struct SubmitBlockRequestWithMetadata {
     pub submission: SubmitBlockRequest,
     pub metadata: BidMetadata,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn validator_slot_data_ser_deser() {
+        let registrations = [
+            r#"
+                {
+                    "slot": "123",
+                    "validator_index": "123",
+                    "entry": {
+                        "message": {
+                            "fee_recipient": "0x0000000000000000000000000000000000000000",
+                            "gas_limit": "60000000",
+                            "timestamp": "123",
+                            "pubkey": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                        },
+                        "signature": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                    }
+                }
+            "#,
+            r#"
+                {
+                    "slot": "123",
+                    "validator_index": "123",
+                    "entry": {
+                        "message": {
+                            "fee_recipient": "0x0000000000000000000000000000000000000000",
+                            "gas_limit": "60000000",
+                            "timestamp": "123",
+                            "pubkey": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                        },
+                        "signature": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                    },
+                    "regional_endpoints": [
+                        {
+                            "name": "",
+                            "region": "",
+                            "http_endpoint": "http://0.0.0.0",
+                            "grpc_endpoint": "grpc://0.0.0.0",
+                            "websocket_endpoint": "ws://0.0.0.0"
+                        }
+                    ]
+                }
+            "#,
+            r#"
+                {
+                    "slot": "123",
+                    "validator_index": "123",
+                    "entry": {
+                        "message": {
+                            "fee_recipient": "0x0000000000000000000000000000000000000000",
+                            "gas_limit": "60000000",
+                            "timestamp": "123",
+                            "pubkey": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                        },
+                        "signature": "0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                    },
+                    "preferences": {
+                        "censoring": false
+                    }
+                }
+            "#,
+        ];
+        for raw in registrations {
+            assert!(serde_json::from_str::<ValidatorSlotData>(raw).is_ok());
+        }
+    }
+}

crates/rbuilder/src/live_builder/payload_events/relay_epoch_cache.rs

@@ -237,6 +237,7 @@ mod test {
                 validator_index: 1,
                 slot: 2,
                 regional_endpoints: Vec::new(),
+                preferences: None,
             },
             adjustment_fee_payer: None,
         }

crates/rbuilder/src/mev_boost/mod.rs

@@ -102,9 +102,10 @@ pub struct RelayConfig {
     /// Flag indicating whether the builder should only submit to rproxy endpoinds if available.
     #[serde(default)]
     pub bloxroute_rproxy_only: bool,
-    /// Adds "filtering=true" as query to the call relay/v1/builder/validators to get all validators (including those filtering OFAC)
-    /// On 2025/06/24 (my birthday!) only supported by ultrasound.
-    /// None -> false
+    /// Retrieves registrations for all validators, including filtering ones.
+    /// For ultrasound relay, the behavior is to add `filtering=true` as a query parameter.
+    /// For titan relay if the value is not set, the registrations will be filtered by `censoring=false` by default.
+    /// If the value is set to `true`, `censoring=true` validators would be included.
     pub ask_for_filtering_validators: Option<bool>,
     /// If we submit a block with a different gas than the one the validator registered with in this relay the relay does not mind.
     /// None -> false
@@ -674,15 +675,25 @@ impl RelayClient {
         let mut headers = HeaderMap::new();
         self.add_auth_headers(&mut headers)
             .map_err(|_| RelayError::InvalidHeader)?;
-        let validators = req
+        let registrations = req
             .headers(headers)
             .send()
             .await?
             .json::<RelayResponse<Vec<ValidatorSlotData>>>()
             .await?;
 
-        match validators {
-            RelayResponse::Ok(validators) => Ok(validators),
+        match registrations {
+            RelayResponse::Ok(registrations) => {
+                let registrations = registrations
+                    .into_iter()
+                    .filter(|r| {
+                        r.preferences
+                            .as_ref()
+                            .is_none_or(|p| !p.censoring || self.ask_for_filtering_validators)
+                    })
+                    .collect();
+                Ok(registrations)
+            }
             RelayResponse::Error(error) => Err(RelayError::RelayError(error)),
         }
     }
@@ -1314,6 +1325,7 @@ mod tests {
                 signature: Default::default(),
             },
             regional_endpoints: Vec::new(),
+            preferences: None,
         };
         relay
             .submit_block(&sub_relay, &registration, true, true, false, false)