chore(p2p): Refactor & Test Bootnode Discovery Configs

[refcell]

Summary

The config-building logic is extracted into dedicated discv4_config() and discv5_config() methods on Command to make each concern testable in isolation. Unit tests using rstest are added to assert the discv5 discovery socket port matches --v5-addr and differs from --v4-addr.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
base	Ignored	Preview	May 1, 2026 7:10pm

[github-actions]

Review Summary

Critical: Discovery port binding is not actually fixed

The PR title mentions a "discv5 NAT fix" and the refactoring extracts config-building into methods, but discv5_config() still passes DEFAULT_DISCOVERY_V5_LISTEN_CONFIG to Discv5ConfigBuilder::new() (line 145). This means the inner discv5 library binds its UDP socket to the default listen config, not to the address from --v5-addr. The full node in node.rs correctly uses ListenConfig::from_two_sockets() / ListenConfig::from_ip() to bind to the configured address. The bootnode should do the same — e.g.:

let listen = ListenConfig::from_ip(self.v5_addr.ip(), self.v5_addr.port());
let mut inner_builder = Discv5ConfigBuilder::new(listen);

Test issues

1. discv5_config_preserves_default_discovery_socket_and_sets_rlpx_socket (line 229): Asserts discovery_socket().port() == DEFAULT_DISCOVERY_V5_PORT, which codifies the current (broken) behavior. Once the fix above is applied, this test would break — making it a regression trap rather than a regression guard. The assertion should be assert_eq!(config.discovery_socket().port(), command.v5_addr.port()).

2. discv4_config_matches_refactored_builder (lines 190-213): Tautological — expected is built with the exact same expression as the method under test. The 16-field comparison adds maintenance cost without meaningful signal. A focused assertion on the external_ip_resolver field (line 213) is sufficient and already present.

Minor

• No runtime validation that v4_addr != v5_addr when --v5 is enabled. Users will get an opaque OS socket-binding error instead of a clear message.

All specific findings are posted as inline comments.