feat(sync): Phase 1 MVP - single relay proactive sync

- Add src/sync/ module with SyncManager
- Add NGIT_SYNC_RELAY_URL config option
- Subscribe to kind 30617 on configured relay
- Validate synced events through Nip34WritePolicy
- Integration test with two TestRelay instances

1 files changed, 22 insertions, 0 deletions

diff --git a/src/sync/mod.rs b/src/sync/mod.rs
new file mode 100644
index 0000000..279471b
--- /dev/null
+++ b/src/sync/mod.rs
@@ -0,0 +1,22 @@
+//! Proactive Sync Module for GRASP-02
+//!
+//! This module implements proactive synchronization of kind 30617 (repository state)
+//! events from configured relay(s). Events are validated through the same write policy
+//! as directly-submitted events.
+
+mod connection;
+mod manager;
+
+pub use manager::SyncManager;
+
+use std::net::SocketAddr;
+
+/// Synthetic source address used for synced events
+///
+/// This distinguishes synced events from directly-submitted events in logs and metrics.
+/// Uses 127.0.0.2:0 as a recognizable "synced event" marker.
+pub const SYNC_SOURCE_ADDR: SocketAddr =
+    SocketAddr::new(std::net::IpAddr::V4(std::net::Ipv4Addr::new(127, 0, 0, 2)), 0);
+
+/// Kind for repository state events (NIP-34)
+pub const KIND_REPOSITORY_STATE: u16 = 30617;
\ No newline at end of file