feat: implement proximity-based update forwarding

[sanity]

Problem

When a peer caches a contract via PUT/GET by calling seed_contract(), it does NOT automatically establish an upstream subscription in the broadcast tree. This creates "disconnected subtrees" where peers cache contracts but never receive UPDATEs for them.

The invariant "caching a contract = being subscribed to updates" is violated.

Why This Matters

1. A peer receives a PUT and caches via seed_contract()
2. Another peer later subscribes through this peer
3. UPDATEs from the root never reach either peer because the first peer has no upstream path

Previous Approach

PR #2002 attempted to solve this but became stale (109 commits behind main) and was invalidated by the PeerId → PeerKeyLocation routing refactor (commit b9bb43fc).

This Solution

Introduce ProximityCacheManager that tracks which contracts each neighbor has cached:

1. Announce on cache: When a peer caches a contract, it broadcasts a CacheAnnounce message to neighbors
2. Track neighbor caches: Neighbors record which contracts each peer has cached
3. Enhanced UPDATE targeting: get_broadcast_targets_update() now combines:
   • Subscribers (explicit downstream interest via subscription tree)
   • Proximity neighbors (nearby seeders who cache the contract)

Design Decision

Keep subscription tree and proximity cache as independent mechanisms, combined only at the broadcast targeting point:

fn get_broadcast_targets_update(key) -> HashSet<PeerKeyLocation> {
    let subscribers = ring.subscribers_of(key);      // downstream interest
    let seeders = proximity_cache.neighbors_with_contract(key);  // nearby cachers
    // HashSet union deduplicates
    subscribers.into_iter().chain(seeders).collect()
}

Rationale:

• Different lifecycle (subscriptions are explicit; seeding follows cache eviction)
• Different data structures and concerns
• But same action needed: send UPDATE to both
• HashSet naturally deduplicates

Changes

• Add ProximityCacheMessage protocol (CacheAnnounce, CacheStateRequest, CacheStateResponse)
• Add ProximityCacheManager to track neighbor contract caches (~220 lines)
• Integrate into OpManager and message routing
• Call announce_contract_cached() after seed_contract() in PUT/GET
• Enhance get_broadcast_targets_update() to include proximity neighbors

Testing

• All existing tests pass (254 passed)
• Added 5 unit tests for ProximityCacheManager
• Clippy clean

Supersedes

Closes #2002

🤖 Generated with Claude Code

[sanity]

@claude Please do a detailed review of this pull request

[claude]

Claude finished @sanity's task —— View job

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PR Review Complete

I've completed a detailed review of the proximity-based update forwarding implementation. Below are my findings organized by category:

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🎯 Overall Assessment

Verdict: The implementation is well-designed and addresses the stated problem effectively. The separation of concerns between subscription tree and proximity cache is clean. However, there are several areas that need attention before merging.

Key Strengths:

• Clear separation: proximity cache is independent from subscription tree
• Natural HashSet deduplication prevents duplicate UPDATE targets
• Good test coverage for ProximityCacheManager (5 unit tests)
• All 254 existing tests pass

Critical Issues Found: 3
Moderate Issues Found: 5
Minor Issues Found: 4

---

🔴 Critical Issues

1. Missing Peer Disconnection Handling (crates/core/src/node/proximity_cache.rs:186-195)

Issue: on_peer_disconnected is marked #[allow(dead_code)] and never called. When a peer disconnects, stale proximity cache entries will remain, causing UPDATE messages to be sent to dead connections.

Impact: Memory leak + failed UPDATE broadcasts to disconnected peers

Recommendation:

• Hook on_peer_disconnected into the actual peer disconnection logic in node/mod.rs or network_bridge
• Add integration test verifying cache cleanup on disconnect

2. Missing Cache State Synchronization on New Connections (crates/core/src/node/proximity_cache.rs:198-201)

Issue: request_cache_state() is marked #[allow(dead_code)] and never used. When a new peer connects, existing neighbors don't exchange cache state, so proximity UPDATE routing will be incomplete until contracts are cached after connection.

Impact: Missed UPDATE propagation to newly connected peers who already have contracts cached

Recommendation:

• Call request_cache_state() during ConnectOp handshake
• Add integration test: peer A caches contract, peer B connects to A, verify B receives cache announcement

3. Infinite Loop Risk in get_broadcast_targets_update (crates/core/src/operations/update.rs:778-794)

Issue: Lines 791-794 look up PeerKeyLocation from SocketAddr using get_peer_by_addr(), but if a socket address is in proximity_cache.neighbors_with_contract() but not in connection_manager, the lookup returns None and the peer is silently skipped.

Race condition scenario:

1. Peer caches contract and announces
2. ProximityCacheManager records neighbor's socket
3. Peer disconnects before UPDATE
4. connection_manager removes peer
5. UPDATE targets are silently missing

Recommendation:

• Add defensive logging when lookup fails
• Consider cleaning proximity cache synchronously with connection drops
• Add integration test for this race condition

---

🟡 Moderate Issues

4. Proximity Cache Eviction Not Implemented (crates/core/src/node/proximity_cache.rs:78-95)

Issue: on_contract_evicted is marked #[allow(dead_code)]. When contracts are evicted from local cache, neighbors are never notified, leading to stale proximity cache entries.

Impact: UPDATEs sent to peers that no longer cache the contract (wasteful but not fatal)

Recommendation:

• Integrate with contract eviction logic in Ring::seed_contract (line 914)
• Call on_contract_evicted when dropping oldest contract

5. Missing Proximity Cache Persistence

Issue: ProximityCacheManager is in-memory only. After restart, all proximity cache information is lost, requiring contracts to be re-cached before UPDATE routing works optimally.

Impact: Reduced UPDATE reliability after node restart until caches repopulate

Recommendation:

• Document this limitation in code comments
• Consider future enhancement: serialize neighbor_caches to disk

6. No Bounded Cache Size

Issue: neighbor_caches can grow unbounded if many peers cache many contracts. No LRU eviction or size limits.

Impact: Memory exhaustion in long-running nodes with many connections

Recommendation:

• Add configurable max entries per neighbor (e.g., 1000 contracts)
• Add total cache size limit (e.g., 100,000 total entries)
• Implement LRU eviction when limits exceeded

7. Broadcast Overhead Not Optimized

Issue: announce_contract_cached (operations/mod.rs:374-393) broadcasts to all connected peers indiscriminately. For nodes with hundreds of connections, this creates significant overhead for every cached contract.

Recommendation:

• Only announce to k-nearest neighbors (matching routing topology)
• Add configuration parameter for announcement fanout

8. Missing Metrics/Observability

Issue: No metrics for proximity cache effectiveness (hit rate, announcement volume, UPDATE targeting).

Recommendation:

• Add counter: proximity_cache_announcements_sent
• Add gauge: proximity_cache_neighbor_count
• Add counter: update_targets_from_proximity vs update_targets_from_subscriptions

---

🟢 Minor Issues / Suggestions

9. Inconsistent Logging Prefixes

Some logs use PROXIMITY_CACHE: prefix, others don't. Consider consistent prefixing for easier grep.

Files: proximity_cache.rs lines 58, 126, update.rs:806

10. Missing Documentation for Design Decision

The PR description explains why subscription tree and proximity cache are kept separate, but this reasoning isn't captured in code comments. Future maintainers might be tempted to merge them.

Recommendation:
Add module-level doc comment to proximity_cache.rs:

//! DESIGN NOTE: Proximity cache is intentionally separate from subscription tree.
//! Different lifecycles (explicit subscriptions vs cache eviction) justify independence.
//! Deduplication happens at broadcast targeting (HashSet union in get_broadcast_targets_update).

11. Test Coverage Gap: Integration Tests

Unit tests cover ProximityCacheManager logic, but there are no integration tests verifying:

• Actual UPDATE propagation to proximity neighbors (not just subscribers)
• Cache announcement broadcast on PUT/GET
• The full scenario from PR description (disconnected subtree problem)

Recommendation:
Add integration test using freenet-test-network:

#[tokio::test]
async fn test_proximity_update_forwarding() {
    // 1. Peer A PUTs contract (caches via seed_contract)
    // 2. Peer B connects to A
    // 3. Peer C subscribes through B
    // 4. Verify C receives UPDATEs (B should be in proximity targets)
}

12. Potential Race in announce_contract_cached

announce_contract_cached is called after seed_contract() in PUT/GET operations. If the contract is evicted immediately (before announcement completes), neighbors receive stale cache info.

Impact: Low probability, but possible

Recommendation:

• Call announcement before marking as seeded
• OR make announcement synchronous with seeding

---

📋 Code Quality

Positive observations:

• Clear separation of concerns
• Good use of tracing for debugging
• Defensive Option handling in socket address lookups
• Proper use of DashMap for concurrent access

Style notes:

• Consistent with existing codebase conventions
• Good error messages with context

---

🧪 Testing Recommendations

1. Add disconnection test:

   #[test]
   fn test_cache_cleanup_on_disconnect() {
       // Verify neighbor_caches entry is removed when peer disconnects
   }

2. Add race condition test:

   #[tokio::test]
   async fn test_concurrent_cache_and_disconnect() {
       // Verify UPDATE targeting doesn't panic if peer disconnects mid-operation
   }

3. Add integration test with freenet-test-network:

   • Reproduce the "disconnected subtree" problem described in PR
   • Verify this PR fixes it

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✅ Approval Blockers

Before merging, I recommend addressing:

1. Critical Overall architecture RFC #1: Implement peer disconnection cleanup
2. Critical NAT traversal #2: Implement cache state exchange on new connections
3. Critical Decentralized email proof-of-concept #3: Add defensive logging for missing peer lookups
4. Moderate Contract-key API #7: Limit broadcast fanout to prevent overhead
5. Minor Karma: decentralized reputation and trust #11: Add at least one integration test demonstrating the fix

Non-blocking (can be follow-up PRs):

• Moderate Peer resource usage balancing #4: Contract eviction handling
• Moderate Intelligent routing #5: Persistence
• Moderate Social credit #6: Bounded cache size
• Moderate Implement join ring op #8: Metrics

---

📝 Summary

This PR successfully implements proximity-based UPDATE forwarding with a clean separation from the subscription tree. The core logic in ProximityCacheManager is solid and well-tested. However, several lifecycle management gaps (disconnection cleanup, cache state sync) need to be addressed before this is production-ready.

The design decision to keep proximity cache independent from subscriptions is correct and well-reasoned. The deduplication via HashSet is elegant.

Recommendation: Request changes for Critical issues #1-3, then approve after fixes.

---

| Branch: feat/proximity-forwarding-v3

[Copilot]

Pull request overview

This PR implements proximity-based UPDATE forwarding to solve the problem of "disconnected subtrees" where peers cache contracts via seed_contract() but never receive UPDATEs because they lack upstream subscriptions in the broadcast tree.

Key Changes:

• Introduces ProximityCacheManager to track which contracts each neighbor has cached
• Adds CacheAnnounce protocol for peers to broadcast their cached contracts to neighbors
• Enhances get_broadcast_targets_update() to include both explicit subscribers and proximity neighbors who cache the contract

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/core/src/node/proximity_cache.rs	New module implementing ProximityCacheManager with announcement, tracking, and query capabilities for neighbor contract caches
crates/core/src/message.rs	Adds ProximityCacheMessage enum and BroadcastProximityCache NodeEvent for the proximity cache protocol
crates/core/src/node/op_state_manager.rs	Integrates ProximityCacheManager into OpManager as a shared Arc field
crates/core/src/operations/mod.rs	Adds announce_contract_cached() helper to broadcast cache announcements when contracts are seeded
crates/core/src/operations/put.rs	Calls announce_contract_cached() after seed_contract() in all PUT operation paths (5 locations)
crates/core/src/operations/get.rs	Calls announce_contract_cached() after seed_contract() in GET operation caching paths (2 locations)
crates/core/src/operations/update.rs	Enhances get_broadcast_targets_update() to combine subscribers and proximity neighbors, with improved logging
crates/core/src/node/network_bridge/p2p_protoc.rs	Implements BroadcastProximityCache event handling to broadcast messages to all connected peers
crates/core/src/node/mod.rs	Adds ProximityCache message handling in both legacy and pure network paths with proper source address validation
crates/core/src/node/testing_impl.rs	Adds handler to ignore BroadcastProximityCache events in test implementation

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[Copilot]

The .clone() call on line 797 is unnecessary since subscribers is not used after this point and can be moved instead. This creates an unnecessary full HashSet clone which could be expensive for large subscriber sets.

Consider changing:

let mut all_targets: HashSet<PeerKeyLocation> = subscribers.clone();

To:

let mut all_targets: HashSet<PeerKeyLocation> = subscribers;

Suggested change

	let mut all_targets: HashSet<PeerKeyLocation> = subscribers.clone();
	let mut all_targets: HashSet<PeerKeyLocation> = subscribers;

[Copilot]

The on_peer_disconnected method is never called when peers actually disconnect, which will cause the proximity cache to accumulate stale peer data indefinitely. This can lead to:

1. Memory leaks as disconnected peer entries are never removed from neighbor_caches
2. Attempting to send UPDATE messages to disconnected peers
3. Inaccurate neighbor contract tracking

The on_peer_disconnected should be called when peers disconnect, for example in the NetworkBridge::drop_connection method or wherever peer disconnections are handled.

Consider integrating this with the existing disconnect handling logic in network_bridge/p2p_protoc.rs around line 82-105 where drop_connection is implemented.

[Copilot]

[nitpick] When handling a CacheAnnounce with both added and removed items, the or_insert_with only uses the added contracts. This means if a peer sends a message with only removed contracts (and an empty added list), and we don't have an existing entry for that peer, we'll create an empty set and then immediately try to remove from it, which is correct behavior.

However, the logic is asymmetric: if this is the first message from a peer and they're announcing removals, we create an empty entry. This could lead to tracking peers with empty cache sets unnecessarily.

Consider adding a check to avoid creating entries for peers that only send removals when we haven't tracked them before, or document this behavior as intentional.

Suggested change

	self.neighbor_caches
	.entry(from)
	.and_modify(|contracts| {
	contracts.extend(added.iter().copied());
	for id in &removed {
	contracts.remove(id);
	}
	})
	.or_insert_with(|| added.into_iter().collect());
	if let Some(mut entry) = self.neighbor_caches.get_mut(&from) {
	entry.extend(added.iter().copied());
	for id in &removed {
	entry.remove(id);
	}
	} else if !added.is_empty() {
	self.neighbor_caches.insert(from, added.into_iter().collect());
	}

[sanity]

Addressed the review feedback in commit 35df827:

Copilot suggestions:

• ✅ Removed unnecessary .clone() in get_broadcast_targets_update (update.rs:778)

Claude bot review - Critical:

• ✅ Implemented peer disconnection cleanup - on_peer_disconnected is now called from the DropConnection handler in p2p_protoc.rs
• ✅ Added defensive logging when peer lookup fails during UPDATE targeting

Claude bot review - Moderate:

• ✅ Fixed CacheAnnounce edge case - remove-only messages no longer create empty entries for unknown neighbors

Claude bot review - Minor:

• ✅ Added design note documentation explaining the two-mechanism architecture (subscription tree vs proximity cache)

The batched removal optimization (30s interval from PR #2002) was intentionally deferred as noted in the plan - immediate announcements are simpler and sufficient for initial implementation.

[AI-assisted - Claude]