fix: finish eth2registration method in cluster/distvalidator

[varex83]

Small PR, was done by testing codex with claude skills (I asked what we can do small but needed -> asked to implement it)

[iamquang95]

@claude

[claude]

Claude finished @iamquang95's task in 1m 56s —— View job

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PR Review

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Summary

This PR implements eth2_registration() in DistValidator, converting the stored BuilderRegistration into a VersionedSignedValidatorRegistration. The implementation is mostly correct but contains one notable correctness issue with the validation logic.

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Findings

[High] Length checks on fixed-size arrays are dead code — validation never fires

crates/cluster/src/distvalidator.rs:112-114

if reg.signature.len() != BLS_SIGNATURE_LEN          // always false
    || reg.message.pub_key.len() != BLS_PUBKEY_LEN    // always false
    || reg.message.fee_recipient.len() != ADDRESS_LEN // always false

Looking at crates/cluster/src/registration.rs:

• signature is phase0::BLSSignature = [u8; 96] — .len() is always 96
• pub_key is phase0::BLSPubKey = [u8; 48] — .len() is always 48
• fee_recipient is [u8; 20] — .len() is always 20

In Rust, fixed-size arrays have a compile-time constant length, so these three conditions are always false. The InvalidRegistration error can only ever be triggered by the gas_limit == 0 or timestamp == 0 checks. The length checks should be replaced with zero-value checks (e.g., reg.signature == [0u8; 96]) or call the existing zero_registration() helper — though note zero_registration() has the same bug with .is_empty() on fixed-size arrays (a pre-existing issue not introduced here).

The idiomatic fix would be:

if reg.signature == [0u8; BLS_SIGNATURE_LEN]
    || reg.message.pub_key == [0u8; BLS_PUBKEY_LEN]
    || reg.message.fee_recipient == [0u8; ADDRESS_LEN]
    || reg.message.gas_limit == 0
    || reg.message.timestamp.timestamp() == 0
{
    return Err(DistValidatorError::InvalidRegistration);
}

Fix this →

[Low] No tests added

The method has no corresponding test. A unit test covering at least the happy path and the zero-registration error path would ensure functional correctness and serve as a regression guard. Ideally a test vector derived from the Go reference (Go charon at v1.7.1) should be included per the project's testing guidelines.

[Low] Pre-existing: zero_registration() is also broken

crates/cluster/src/distvalidator.rs:98-104

The existing zero_registration() method uses .is_empty() on fixed-size arrays, which always returns false. This means zero_registration() always returns false, and callers relying on it are silently broken. This is not introduced by this PR, but is worth fixing alongside this change.

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Parity Matrix

Component	Go ref (v1.7.1)	Rust	Match	Notes
Return type	eth2api.VersionedSignedValidatorRegistration	VersionedSignedValidatorRegistration	yes
Zero-registration check	validates non-empty fields	length checks (always pass)	no	Fixed-size array lengths are constant
Timestamp conversion	int64 → direct	i64.try_into::<u64>()	yes	Negative timestamps map to InvalidRegistration
Field mapping	direct copy	direct copy	yes

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[iamquang95]

The finding is valid, but the zero_registration has bug also please fix the zero_registration as well, it's call is_empty on a fixed size array

[emlautarom1]

Agree with the comments from @iamquang95.