feat(validator): durable EIP-3076 slashing protection

CLAUDE.md

@@ -846,8 +846,10 @@ transitions are in `ethlambda-types`, per the section above. Nothing above
   aggregate when `verified_sync_aggregate` fails (see `docs/spec_deviations.md`).
   `SlotClock` picks the
   offsets by each slot's own fork, and `/eth/v1/config/spec` supplies them. It
-  still keeps no slashing-protection record; PTC votes have an in-memory
-  `(validator, slot)` dedup only, and envelopes are unguarded.
+  keeps EIP-3076 minimal-watermark slashing protection in
+  `--validators-dir/slashing_protection.json` (`crate::slashing_protection`),
+  durable before every block and attestation signature; PTC votes have an
+  in-memory `(validator, slot)` dedup only, and envelopes are unguarded.
   `get_head_node` is one bottom-up walk for every fork, with
   the current slot's fork selecting the payload rules and the boost gate, so a
   follower on any network that schedules gloas (Sepolia does) pays work

README.md

@@ -332,13 +332,14 @@ payload envelope and the payload timeliness vote. It talks to a beacon node over
 the standard Beacon API, so it works against `ethlambda beacon` (run with the
 `--execution-*` flags) or any other conformant beacon node.
 
-> **Warning:** the validator client keeps no slashing-protection record yet.
-> Slashing protection is a work in progress and will be added soon. Until then,
-> do not run the same keys in another client while this one runs, and treat a
-> restart with the same care as a manual key move. Read
-> [Spec deviations](./docs/spec_deviations.md#the-validator-client-keeps-no-slashing-protection-record)
-> before using keys that hold real stake. The client repeats this warning at
-> startup.
+> **Slashing protection:** every block and attestation is checked against a
+> durable per-validator record in `--validators-dir` before it is signed, and a
+> second validator client pointed at the same directory refuses to start. A key
+> with no record is refused at startup: pass `--init-slashing-protection` once,
+> and only for keys that have signed nothing anywhere for at least two epochs.
+> Importing history from another client is not supported yet, so never run
+> these keys in another client at the same time. See
+> [Spec deviations](./docs/spec_deviations.md#the-validator-client-keeps-eip-3076s-minimal-watermarks-not-full-history).
 
 ```sh
 ./target/release/ethlambda validator \

bin/ethlambda/src/validator.rs

@@ -78,6 +78,19 @@ pub(crate) struct ValidatorOptions {
     /// beyond localhost must front it with TLS.
     #[arg(long, default_value = "false")]
     pub(crate) enable_keymanager: bool,
+
+    /// Register every loaded key that has no slashing-protection record,
+    /// instead of refusing to start.
+    ///
+    /// DANGEROUS. Use it only for keys that are brand new, or that have signed
+    /// nothing anywhere for at least two epochs. A key is registered as if it
+    /// had signed a block and an attestation at the current slot and epoch,
+    /// which closes the double-vote window for a key that signed a moment ago
+    /// elsewhere, but not a surround vote against older history. Keys that
+    /// already have a record keep it, so the flag never lowers one; remove it
+    /// once the keys are registered.
+    #[arg(long, default_value = "false")]
+    pub(crate) init_slashing_protection: bool,
 }
 
 impl ValidatorOptions {
@@ -154,6 +167,7 @@ pub(crate) async fn run(options: ValidatorOptions) -> eyre::Result<()> {
         keymanager: options
             .enable_keymanager
             .then(|| std::net::SocketAddr::new(options.http_address, options.keymanager_port)),
+        init_slashing_protection: options.init_slashing_protection,
     })
     .await
     .map_err(Into::into)
@@ -174,6 +188,7 @@ mod tests {
             graffiti: graffiti.to_string(),
             suggested_fee_recipient: None,
             enable_keymanager: false,
+            init_slashing_protection: false,
         }
     }
 

crates/net/rpc/src/beacon/validator_client_tests.rs

@@ -1488,6 +1488,7 @@ mod gloas {
                     None,
                 ),
             ),
+            ethlambda_validator::slashing_protection::SlashingProtection::in_memory(),
         );
         let duty = ProposerDutyDto {
             pubkey: encode_hex(&pubkey.0),
@@ -1606,6 +1607,7 @@ mod gloas {
                     None,
                 ),
             ),
+            ethlambda_validator::slashing_protection::SlashingProtection::in_memory(),
         );
         let duty = ProposerDutyDto {
             pubkey: encode_hex(&pubkey.0),

crates/validator/Cargo.toml

@@ -26,10 +26,11 @@ serde_yaml_ng.workspace = true
 hex.workspace = true
 thiserror.workspace = true
 tracing.workspace = true
-# `time` for the duty loop's sleep between slots. Declared here rather than
-# relied on through workspace feature unification, so this crate still builds
-# if it is ever compiled on its own.
-tokio = { workspace = true, features = ["time", "macros"] }
+# `time` for the duty loop's sleep between slots, `rt` for `spawn_blocking`,
+# which keeps the slashing-protection record's disk flush off the executor.
+# Declared here rather than relied on through workspace feature unification,
+# so this crate still builds if it is ever compiled on its own.
+tokio = { workspace = true, features = ["time", "macros", "rt"] }
 reqwest = { workspace = true, features = ["json"] }
 
 # BLS12-381. Same version and backend the state transition verifies with, so a