2 files changed, 488 insertions, 0 deletions

diff --git a/src/sync/health.rs b/src/sync/health.rs
new file mode 100644
index 0000000..51bd5ae
--- /dev/null
+++ b/src/sync/health.rs
@@ -0,0 +1,475 @@
+//! Relay Health Tracking for GRASP-02 Proactive Sync
+//!
+//! This module implements health tracking for relay connections, including:
+//! - Health state machine (Healthy -> Degraded -> Dead)
+//! - Exponential backoff with configurable max delay
+//! - Dead relay detection after 24h of continuous failures
+//!
+//! ## Health States
+//!
+//! - **Healthy**: Working connection, no recent failures
+//! - **Degraded**: Connection failed, retrying with backoff
+//! - **Dead**: 24h+ of continuous failures, minimal retry (once per day)
+
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use dashmap::DashMap;
+
+use crate::config::Config;
+
+/// Duration threshold before a relay is considered dead (24 hours)
+const DEAD_THRESHOLD_HOURS: u64 = 24;
+
+/// How often dead relays are retried (once per 24 hours)
+const DEAD_RETRY_INTERVAL_HOURS: u64 = 24;
+
+/// Default maximum backoff duration in seconds (1 hour)
+const DEFAULT_MAX_BACKOFF_SECS: u64 = 3600;
+
+/// Base backoff duration in seconds
+const BASE_BACKOFF_SECS: u64 = 5;
+
+/// Health state of a relay connection
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum HealthState {
+    /// Working connection, no recent failures
+    Healthy,
+    /// Connection failed, retrying with exponential backoff
+    Degraded,
+    /// 24h+ of continuous failures, minimal retry
+    Dead,
+}
+
+impl std::fmt::Display for HealthState {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            HealthState::Healthy => write!(f, "healthy"),
+            HealthState::Degraded => write!(f, "degraded"),
+            HealthState::Dead => write!(f, "dead"),
+        }
+    }
+}
+
+/// Health information for a single relay
+#[derive(Debug, Clone)]
+pub struct RelayHealth {
+    /// Current health state
+    pub state: HealthState,
+    /// Number of consecutive connection failures
+    pub consecutive_failures: u32,
+    /// Time of the first failure in the current failure streak
+    pub first_failure_time: Option<Instant>,
+    /// Time of the last failure
+    pub last_failure_time: Option<Instant>,
+    /// Time of the last successful connection
+    pub last_success_time: Option<Instant>,
+    /// Next time a connection attempt should be made
+    pub next_retry_at: Option<Instant>,
+}
+
+impl Default for RelayHealth {
+    fn default() -> Self {
+        Self {
+            state: HealthState::Healthy,
+            consecutive_failures: 0,
+            first_failure_time: None,
+            last_failure_time: None,
+            last_success_time: None,
+            next_retry_at: None,
+        }
+    }
+}
+
+impl RelayHealth {
+    /// Create a new RelayHealth with healthy state
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
+/// Thread-safe relay health tracker using DashMap
+#[derive(Debug)]
+pub struct RelayHealthTracker {
+    health: DashMap<String, RelayHealth>,
+    max_backoff_secs: u64,
+}
+
+impl RelayHealthTracker {
+    /// Create a new RelayHealthTracker
+    pub fn new(config: &Config) -> Self {
+        Self {
+            health: DashMap::new(),
+            max_backoff_secs: config.sync_max_backoff_secs,
+        }
+    }
+
+    /// Create a new RelayHealthTracker with default settings
+    pub fn with_defaults() -> Self {
+        Self {
+            health: DashMap::new(),
+            max_backoff_secs: DEFAULT_MAX_BACKOFF_SECS,
+        }
+    }
+
+    /// Create a new RelayHealthTracker with custom max backoff
+    pub fn with_max_backoff(max_backoff_secs: u64) -> Self {
+        Self {
+            health: DashMap::new(),
+            max_backoff_secs,
+        }
+    }
+
+    /// Record a successful connection to a relay
+    ///
+    /// Resets the relay to Healthy state and clears failure counters.
+    pub fn record_success(&self, relay_url: &str) {
+        let now = Instant::now();
+        let mut entry = self.health.entry(relay_url.to_string()).or_default();
+        let health = entry.value_mut();
+
+        let old_state = health.state;
+
+        // Reset to healthy state
+        health.state = HealthState::Healthy;
+        health.consecutive_failures = 0;
+        health.first_failure_time = None;
+        health.last_failure_time = None;
+        health.last_success_time = Some(now);
+        health.next_retry_at = None;
+
+        if old_state != HealthState::Healthy {
+            tracing::info!(
+                "Relay {} recovered to healthy (was {:?})",
+                relay_url,
+                old_state
+            );
+        }
+    }
+
+    /// Record a connection failure for a relay
+    ///
+    /// Increments failure counter, updates state, and calculates next retry time.
+    pub fn record_failure(&self, relay_url: &str) {
+        let now = Instant::now();
+        let mut entry = self.health.entry(relay_url.to_string()).or_default();
+        let health = entry.value_mut();
+
+        let old_state = health.state;
+
+        // Set first_failure_time if this is a new failure streak
+        if health.first_failure_time.is_none() {
+            health.first_failure_time = Some(now);
+        }
+
+        health.consecutive_failures = health.consecutive_failures.saturating_add(1);
+        health.last_failure_time = Some(now);
+
+        // Check if we should transition to Dead state
+        if let Some(first_failure) = health.first_failure_time {
+            let failure_duration = now.duration_since(first_failure);
+            let dead_threshold = Duration::from_secs(DEAD_THRESHOLD_HOURS * 3600);
+
+            if failure_duration >= dead_threshold {
+                health.state = HealthState::Dead;
+                // Dead relays retry once per day
+                health.next_retry_at =
+                    Some(now + Duration::from_secs(DEAD_RETRY_INTERVAL_HOURS * 3600));
+
+                if old_state != HealthState::Dead {
+                    tracing::warn!(
+                        "Relay {} marked dead after 24h failures ({} consecutive failures)",
+                        relay_url,
+                        health.consecutive_failures
+                    );
+                }
+            } else {
+                // Degraded state with exponential backoff
+                health.state = HealthState::Degraded;
+                let backoff = Self::get_backoff_duration(
+                    health.consecutive_failures,
+                    self.max_backoff_secs,
+                );
+                health.next_retry_at = Some(now + backoff);
+
+                if old_state != HealthState::Degraded {
+                    tracing::warn!(
+                        "Relay {} degraded, backoff {:?}",
+                        relay_url,
+                        backoff
+                    );
+                } else {
+                    tracing::debug!(
+                        "Relay {} failure #{}, backoff {:?}",
+                        relay_url,
+                        health.consecutive_failures,
+                        backoff
+                    );
+                }
+            }
+        }
+    }
+
+    /// Check if a connection attempt should be made to a relay
+    ///
+    /// Returns true if:
+    /// - The relay has no health record (first attempt)
+    /// - The relay is healthy
+    /// - The backoff period has elapsed
+    pub fn should_attempt_connection(&self, relay_url: &str) -> bool {
+        let entry = self.health.get(relay_url);
+
+        match entry {
+            None => true, // No record, allow first attempt
+            Some(entry) => {
+                let health = entry.value();
+
+                match health.state {
+                    HealthState::Healthy => true,
+                    HealthState::Degraded | HealthState::Dead => {
+                        // Check if backoff period has elapsed
+                        match health.next_retry_at {
+                            None => true,
+                            Some(next_retry) => Instant::now() >= next_retry,
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    /// Get the current health state of a relay
+    pub fn get_state(&self, relay_url: &str) -> HealthState {
+        self.health
+            .get(relay_url)
+            .map(|entry| entry.value().state)
+            .unwrap_or(HealthState::Healthy)
+    }
+
+    /// Check if a relay is marked as dead
+    pub fn is_dead(&self, relay_url: &str) -> bool {
+        self.get_state(relay_url) == HealthState::Dead
+    }
+
+    /// Get the remaining backoff duration for a relay
+    ///
+    /// Returns None if no backoff is active.
+    pub fn get_remaining_backoff(&self, relay_url: &str) -> Option<Duration> {
+        let entry = self.health.get(relay_url)?;
+        let health = entry.value();
+        let next_retry = health.next_retry_at?;
+        let now = Instant::now();
+
+        if now >= next_retry {
+            None
+        } else {
+            Some(next_retry - now)
+        }
+    }
+
+    /// Get the consecutive failure count for a relay
+    pub fn get_failure_count(&self, relay_url: &str) -> u32 {
+        self.health
+            .get(relay_url)
+            .map(|entry| entry.value().consecutive_failures)
+            .unwrap_or(0)
+    }
+
+    /// Calculate the backoff duration based on failure count
+    ///
+    /// Uses exponential backoff: base * 2^failures, capped at max_backoff
+    pub fn get_backoff_duration(consecutive_failures: u32, max_backoff_secs: u64) -> Duration {
+        let backoff_secs = BASE_BACKOFF_SECS
+            .saturating_mul(2u64.saturating_pow(consecutive_failures.saturating_sub(1)));
+        Duration::from_secs(backoff_secs.min(max_backoff_secs))
+    }
+
+    /// Get all tracked relay URLs
+    pub fn get_tracked_relays(&self) -> Vec<String> {
+        self.health.iter().map(|entry| entry.key().clone()).collect()
+    }
+
+    /// Get a clone of the health info for a relay
+    pub fn get_health(&self, relay_url: &str) -> Option<RelayHealth> {
+        self.health.get(relay_url).map(|entry| entry.value().clone())
+    }
+}
+
+/// Create a shared RelayHealthTracker wrapped in Arc
+pub fn create_health_tracker(config: &Config) -> Arc<RelayHealthTracker> {
+    Arc::new(RelayHealthTracker::new(config))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_health_state_display() {
+        assert_eq!(HealthState::Healthy.to_string(), "healthy");
+        assert_eq!(HealthState::Degraded.to_string(), "degraded");
+        assert_eq!(HealthState::Dead.to_string(), "dead");
+    }
+
+    #[test]
+    fn test_default_health_is_healthy() {
+        let health = RelayHealth::default();
+        assert_eq!(health.state, HealthState::Healthy);
+        assert_eq!(health.consecutive_failures, 0);
+        assert!(health.first_failure_time.is_none());
+    }
+
+    #[test]
+    fn test_should_attempt_connection_new_relay() {
+        let tracker = RelayHealthTracker::with_defaults();
+        assert!(tracker.should_attempt_connection("wss://new-relay.example.com"));
+    }
+
+    #[test]
+    fn test_record_success_resets_to_healthy() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let url = "wss://test-relay.example.com";
+
+        // Simulate a few failures
+        tracker.record_failure(url);
+        tracker.record_failure(url);
+        assert_eq!(tracker.get_state(url), HealthState::Degraded);
+        assert_eq!(tracker.get_failure_count(url), 2);
+
+        // Record success
+        tracker.record_success(url);
+        assert_eq!(tracker.get_state(url), HealthState::Healthy);
+        assert_eq!(tracker.get_failure_count(url), 0);
+        assert!(tracker.should_attempt_connection(url));
+    }
+
+    #[test]
+    fn test_backoff_increases_exponentially() {
+        // failure 1: 5s
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(1, 3600),
+            Duration::from_secs(5)
+        );
+        // failure 2: 10s
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(2, 3600),
+            Duration::from_secs(10)
+        );
+        // failure 3: 20s
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(3, 3600),
+            Duration::from_secs(20)
+        );
+        // failure 4: 40s
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(4, 3600),
+            Duration::from_secs(40)
+        );
+        // failure 5: 80s
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(5, 3600),
+            Duration::from_secs(80)
+        );
+    }
+
+    #[test]
+    fn test_backoff_capped_at_max() {
+        let max_backoff = 3600u64;
+        // After many failures, should cap at max_backoff (1 hour)
+        assert_eq!(
+            RelayHealthTracker::get_backoff_duration(20, max_backoff),
+            Duration::from_secs(max_backoff)
+        );
+    }
+
+    #[test]
+    fn test_degraded_state_after_failure() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let url = "wss://test-relay.example.com";
+
+        tracker.record_failure(url);
+        assert_eq!(tracker.get_state(url), HealthState::Degraded);
+        assert_eq!(tracker.get_failure_count(url), 1);
+    }
+
+    #[test]
+    fn test_backoff_blocks_immediate_reconnection() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let url = "wss://test-relay.example.com";
+
+        tracker.record_failure(url);
+
+        // Immediately after failure, should not attempt (backoff active)
+        assert!(!tracker.should_attempt_connection(url));
+
+        // Remaining backoff should be some positive duration
+        let remaining = tracker.get_remaining_backoff(url);
+        assert!(remaining.is_some());
+        assert!(remaining.unwrap() > Duration::ZERO);
+    }
+
+    #[test]
+    fn test_is_dead() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let url = "wss://test-relay.example.com";
+
+        // Initially not dead
+        assert!(!tracker.is_dead(url));
+
+        // After a failure, still not dead (just degraded)
+        tracker.record_failure(url);
+        assert!(!tracker.is_dead(url));
+        assert_eq!(tracker.get_state(url), HealthState::Degraded);
+    }
+
+    #[test]
+    fn test_get_tracked_relays() {
+        let tracker = RelayHealthTracker::with_defaults();
+
+        tracker.record_success("wss://relay1.example.com");
+        tracker.record_failure("wss://relay2.example.com");
+
+        let tracked = tracker.get_tracked_relays();
+        assert_eq!(tracked.len(), 2);
+        assert!(tracked.contains(&"wss://relay1.example.com".to_string()));
+        assert!(tracked.contains(&"wss://relay2.example.com".to_string()));
+    }
+
+    #[test]
+    fn test_custom_max_backoff() {
+        let custom_max = 60u64; // 1 minute max
+        let tracker = RelayHealthTracker::with_max_backoff(custom_max);
+        let url = "wss://test-relay.example.com";
+
+        // Simulate many failures
+        for _ in 0..20 {
+            tracker.record_failure(url);
+        }
+
+        // The remaining backoff should respect the custom max
+        // Note: We can't easily test the internal backoff calculation here,
+        // but we can verify the tracker was created with the custom setting
+        assert_eq!(tracker.max_backoff_secs, custom_max);
+    }
+
+    #[test]
+    fn test_get_health_returns_clone() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let url = "wss://test-relay.example.com";
+
+        tracker.record_success(url);
+        let health = tracker.get_health(url);
+
+        assert!(health.is_some());
+        let health = health.unwrap();
+        assert_eq!(health.state, HealthState::Healthy);
+        assert!(health.last_success_time.is_some());
+    }
+
+    #[test]
+    fn test_get_health_nonexistent() {
+        let tracker = RelayHealthTracker::with_defaults();
+        let health = tracker.get_health("wss://nonexistent.example.com");
+        assert!(health.is_none());
+    }
+}
\ No newline at end of file
diff --git a/src/sync/mod.rs b/src/sync/mod.rs
index fb09896..9ac62ed 100644
--- a/src/sync/mod.rs
+++ b/src/sync/mod.rs
@@ -14,6 +14,7 @@
 
 pub mod algorithms;
 pub mod filters;
+pub mod health;
 pub mod relay_connection;
 pub mod self_subscriber;
 
@@ -26,6 +27,9 @@ pub use relay_connection::{RelayConnection, RelayEvent};
 // Re-export self-subscriber types
 pub use self_subscriber::{RelayAction, SelfSubscriber};
 
+// Re-export health tracking types
+pub use health::RelayHealthTracker;
+
 use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 
@@ -339,6 +343,12 @@ pub struct SyncManager {
     relay_sync_index: RelaySyncIndex,
     /// In-flight subscription batches
     pending_sync_index: PendingSyncIndex,
+    /// Active relay connections - keyed by relay URL
+    connections: HashMap<String, RelayConnection>,
+    /// Health tracker for relay connection state
+    health_tracker: Arc<RelayHealthTracker>,
+    /// Counter for generating unique batch IDs
+    next_batch_id: u64,
 }
 
 impl SyncManager {
@@ -366,6 +376,9 @@ impl SyncManager {
             repo_sync_index: Arc::new(RwLock::new(HashMap::new())),
             relay_sync_index: Arc::new(RwLock::new(HashMap::new())),
             pending_sync_index: Arc::new(RwLock::new(HashMap::new())),
+            connections: HashMap::new(),
+            health_tracker: Arc::new(RelayHealthTracker::new(config)),
+            next_batch_id: 0,
         }
     }