crates/simulation/src/distribution/properties.rs

@@ -326,3 +326,173 @@ pub fn check_convergence(
         description: "Membership views converge after faults stabilize".into(),
     }
 }
+
+// ─── Registry & Lifecycle Property Checks ─────────────────────────────────
+
+/// Check that all alive nodes have at least `min_registry_size` registry entries at the end.
+pub fn check_registry_propagation(
+    trace: &DistTrace,
+    min_registry_size: usize,
+) -> crate::properties::PropertyResult {
+    let passed = if let Some(last_round) = trace.snapshots_per_round.last() {
+        last_round
+            .iter()
+            .filter(|(_, s)| s.is_alive)
+            .all(|(_, s)| s.registry_size >= min_registry_size)
+    } else {
+        false
+    };
+    let actual = if let Some(last_round) = trace.snapshots_per_round.last() {
+        let sizes: Vec<usize> = last_round
+            .iter()
+            .filter(|(_, s)| s.is_alive)
+            .map(|(_, s)| s.registry_size)
+            .collect();
+        format!("{sizes:?}")
+    } else {
+        "no data".into()
+    };
+    crate::properties::PropertyResult {
+        name: "registry_propagation".into(),
+        category: "Registry".into(),
+        passed,
+        expected: format!("all alive nodes have ≥{min_registry_size} registry entries"),
+        actual,
+        description: "Registry entries propagate to all nodes via gossip".into(),
+    }
+}
+
+/// Check that all alive nodes agree on registry tombstone count at the end.
+pub fn check_registry_tombstones(
+    trace: &DistTrace,
+    min_tombstones: usize,
+) -> crate::properties::PropertyResult {
+    let passed = if let Some(last_round) = trace.snapshots_per_round.last() {
+        last_round
+            .iter()
+            .filter(|(_, s)| s.is_alive)
+            .all(|(_, s)| s.registry_tombstone_count >= min_tombstones)
+    } else {
+        false
+    };
+    let actual = if let Some(last_round) = trace.snapshots_per_round.last() {
+        let counts: Vec<usize> = last_round
+            .iter()
+            .filter(|(_, s)| s.is_alive)
+            .map(|(_, s)| s.registry_tombstone_count)
+            .collect();
+        format!("{counts:?}")
+    } else {
+        "no data".into()
+    };
+    crate::properties::PropertyResult {
+        name: "registry_tombstones".into(),
+        category: "Registry".into(),
+        passed,
+        expected: format!("all alive nodes have ≥{min_tombstones} tombstones"),
+        actual,
+        description: "Registry tombstones propagate to all nodes".into(),
+    }
+}
+
+/// Check that at least one survivor has a non-empty repair queue after a node death.
+pub fn check_repair_queue_populated(
+    trace: &DistTrace,
+    after_round: usize,
+) -> crate::properties::PropertyResult {
+    let populated = trace
+        .snapshots_per_round
+        .iter()
+        .skip(after_round)
+        .any(|round_snaps| {
+            round_snaps
+                .iter()
+                .any(|(_, s)| s.is_alive && s.repair_queue_size > 0)
+        });
+    crate::properties::PropertyResult {
+        name: "repair_queue_populated".into(),
+        category: "Lifecycle".into(),
+        passed: populated,
+        expected: format!("repair queue populated after round {after_round}"),
+        actual: if populated {
+            "populated".into()
+        } else {
+            let final_sizes: Vec<usize> = trace
+                .snapshots_per_round
+                .last()
+                .map(|r| {
+                    r.iter()
+                        .filter(|(_, s)| s.is_alive)
+                        .map(|(_, s)| s.repair_queue_size)
+                        .collect()
+                })
+                .unwrap_or_default();
+            format!("final repair_queue_sizes: {final_sizes:?}")
+        },
+        description: "Repair queue populated after node death".into(),
+    }
+}
+
+/// Check that routing_table_size ≤ alive_count for all alive nodes at every round.
+pub fn check_routing_table_bounded(
+    trace: &DistTrace,
+) -> crate::properties::PropertyResult {
+    let mut violation = None;
+
+    for (round_idx, round_snaps) in trace.snapshots_per_round.iter().enumerate() {
+        let alive_count = round_snaps.iter().filter(|(_, s)| s.is_alive).count();
+        for (name, snap) in round_snaps {
+            if snap.is_alive && snap.routing_table_size > alive_count {
+                violation = Some(format!(
+                    "round {}: {} has routing_table_size={} but alive_count={}",
+                    round_idx + 1, name, snap.routing_table_size, alive_count
+                ));
+                break;
+            }
+        }
+        if violation.is_some() {
+            break;
+        }
+    }
+
+    crate::properties::PropertyResult {
+        name: "routing_table_bounded".into(),
+        category: "Invariant".into(),
+        passed: violation.is_none(),
+        expected: "routing_table_size ≤ alive_count at every round".into(),
+        actual: violation.unwrap_or_else(|| "all within bounds".into()),
+        description: "Routing table never exceeds alive membership".into(),
+    }
+}
+
+/// Check that cache_size ≤ cache_capacity for all alive nodes at every round.
+pub fn check_cache_bounded(
+    trace: &DistTrace,
+    cache_capacity: usize,
+) -> crate::properties::PropertyResult {
+    let mut violation = None;
+
+    for (round_idx, round_snaps) in trace.snapshots_per_round.iter().enumerate() {
+        for (name, snap) in round_snaps {
+            if snap.is_alive && snap.cache_size > cache_capacity {
+                violation = Some(format!(
+                    "round {}: {} has cache_size={} but capacity={}",
+                    round_idx + 1, name, snap.cache_size, cache_capacity
+                ));
+                break;
+            }
+        }
+        if violation.is_some() {
+            break;
+        }
+    }
+
+    crate::properties::PropertyResult {
+        name: "cache_bounded".into(),
+        category: "Invariant".into(),
+        passed: violation.is_none(),
+        expected: format!("cache_size ≤ {cache_capacity} at every round"),
+        actual: violation.unwrap_or_else(|| "all within bounds".into()),
+        description: "Cache never exceeds configured capacity".into(),
+    }
+}

crates/simulation/src/distribution/sim.rs

@@ -21,6 +21,17 @@ pub struct Partition {
     pub asymmetric: bool,
 }
 
+/// An action to execute at a specific round during the simulation.
+#[derive(Debug, Clone)]
+pub enum SimAction {
+    /// Register a name on the given node, binding it to a fresh random actor.
+    RegisterName { node_idx: usize, name: String },
+    /// Register a name on the given node, binding it to a specific actor address.
+    RegisterNameWithActor { node_idx: usize, name: String, actor: ActorAddress },
+    /// Unregister a name on the given node (creates a tombstone).
+    UnregisterName { node_idx: usize, name: String },
+}
+
 /// Schedule entry for network faults.
 #[derive(Debug, Clone)]
 pub enum NetworkFault {
@@ -49,6 +60,12 @@ pub struct DistributionSimConfig {
     pub cache_capacity: usize,
     /// Network fault schedule.
     pub network_faults: Vec<NetworkFault>,
+    /// Actions to execute at specific rounds (e.g. register/unregister names).
+    pub action_schedule: Vec<(usize, SimAction)>,
+    /// Custom registry config overrides.
+    pub registry_tombstone_ttl: Option<u64>,
+    pub registry_gc_interval: Option<u64>,
+    pub registry_dissemination_lambda: Option<usize>,
 }
 
 impl Default for DistributionSimConfig {
@@ -70,6 +87,10 @@ impl Default for DistributionSimConfig {
             revive_schedule: Vec::new(),
             cache_capacity: 100,
             network_faults: Vec::new(),
+            action_schedule: Vec::new(),
+            registry_tombstone_ttl: None,
+            registry_gc_interval: None,
+            registry_dissemination_lambda: None,
         }
     }
 }
@@ -134,11 +155,25 @@ impl NetworkState {
 
 type DistTrace = SimulationTrace<DistributionEventKind, DistributionSnapshot>;
 
+/// Run a distribution simulation, returning both the trace and the final node states.
+///
+/// The returned `Vec<Option<DistributedNode>>` has the same length as `config.num_nodes`.
+/// Dead nodes are `None`.
+pub fn run_simulation_with_nodes(config: DistributionSimConfig) -> (DistTrace, Vec<Option<DistributedNode>>) {
+    let (trace, nodes, _) = run_simulation_inner(config);
+    (trace, nodes)
+}
+
 /// Run a distribution simulation.
 ///
 /// Creates N `DistributedNode` instances, forms a cluster via join protocol,
 /// registers actors, then runs rounds of tick + deliver + resolve.
 pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
+    let (trace, _, _) = run_simulation_inner(config);
+    trace
+}
+
+fn run_simulation_inner(config: DistributionSimConfig) -> (DistTrace, Vec<Option<DistributedNode>>, Vec<NodeId>) {
     let mut events: Vec<Event<DistributionEventKind>> = Vec::new();
     let mut snapshots_per_round: Vec<Vec<(String, DistributionSnapshot)>> = Vec::new();
 
@@ -152,13 +187,14 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
 
     for i in 0..n {
         let addr: SocketAddr = format!("127.0.0.1:{}", 10001 + i).parse().unwrap();
-        let node_config = DistributedNodeConfig {
+        let mut node_config = DistributedNodeConfig {
             listen_addr: addr,
             swim: config.swim.clone(),
             cache_capacity: config.cache_capacity,
             republish_interval: 50,
             ..Default::default()
         };
+        apply_registry_overrides(&mut node_config, &config);
         let node = DistributedNode::new(node_config);
         node_ids.push(node.node_id());
         addrs.push(addr);
@@ -284,13 +320,14 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
         // Apply revive schedule.
         for &(revive_round, revive_idx) in &config.revive_schedule {
             if revive_round == round && revive_idx < n {
-                let node_config = DistributedNodeConfig {
+                let mut node_config = DistributedNodeConfig {
                     listen_addr: addrs[revive_idx],
                     swim: config.swim.clone(),
                     cache_capacity: config.cache_capacity,
                     republish_interval: 50,
                     ..Default::default()
                 };
+                apply_registry_overrides(&mut node_config, &config);
                 let revived = DistributedNode::new(node_config);
                 // Rejoin the cluster.
                 let join_actions = revived.join(&[seed_addr]);
@@ -328,6 +365,60 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
             }
         }
 
+        // Execute scheduled actions for this round.
+        for (action_round, action) in &config.action_schedule {
+            if *action_round == round {
+                match action {
+                    SimAction::RegisterName { node_idx, name } => {
+                        if *node_idx < n {
+                            if let Some(ref mut node) = nodes[*node_idx] {
+                                let actor = ActorAddress::new_random();
+                                node.register_name(name.clone(), actor);
+                                events.push(Event {
+                                    tick: round as u64,
+                                    node_name: node_names[*node_idx].clone(),
+                                    kind: DistributionEventKind::NameRegistered {
+                                        name: name.clone(),
+                                        node_idx: *node_idx,
+                                    },
+                                });
+                            }
+                        }
+                    }
+                    SimAction::RegisterNameWithActor { node_idx, name, actor } => {
+                        if *node_idx < n {
+                            if let Some(ref mut node) = nodes[*node_idx] {
+                                node.register_name(name.clone(), *actor);
+                                events.push(Event {
+                                    tick: round as u64,
+                                    node_name: node_names[*node_idx].clone(),
+                                    kind: DistributionEventKind::NameRegistered {
+                                        name: name.clone(),
+                                        node_idx: *node_idx,
+                                    },
+                                });
+                            }
+                        }
+                    }
+                    SimAction::UnregisterName { node_idx, name } => {
+                        if *node_idx < n {
+                            if let Some(ref mut node) = nodes[*node_idx] {
+                                node.unregister_name(name);
+                                events.push(Event {
+                                    tick: round as u64,
+                                    node_name: node_names[*node_idx].clone(),
+                                    kind: DistributionEventKind::NameUnregistered {
+                                        name: name.clone(),
+                                        node_idx: *node_idx,
+                                    },
+                                });
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
         // Tick all live nodes and deliver actions.
         for _ in 0..config.ticks_per_round {
             tick_all_and_deliver(
@@ -393,6 +484,8 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
                     directory_entry_count: node.directory().entry_count(),
                     cache_size: node.cache().len(),
                     repair_queue_size: node.repair_queue().len(),
+                    registry_size: node.registry().len(),
+                    registry_tombstone_count: node.registry().tombstone_count(),
                     is_alive: true,
                 },
                 None => DistributionSnapshot {
@@ -401,6 +494,8 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
                     directory_entry_count: 0,
                     cache_size: 0,
                     repair_queue_size: 0,
+                    registry_size: 0,
+                    registry_tombstone_count: 0,
                     is_alive: false,
                 },
             };
@@ -414,13 +509,26 @@ pub fn run_simulation(config: DistributionSimConfig) -> DistTrace {
         .map(|i| (node_names[i].clone(), node_names[0].clone()))
         .collect();
 
-    SimulationTrace {
+    let trace = SimulationTrace {
         name: config.name,
         node_names,
         topology_edges,
         events,
         snapshots_per_round,
         num_rounds: config.num_rounds,
+    };
+    (trace, nodes, node_ids)
+}
+
+fn apply_registry_overrides(node_config: &mut DistributedNodeConfig, config: &DistributionSimConfig) {
+    if let Some(ttl) = config.registry_tombstone_ttl {
+        node_config.registry.tombstone_ttl = ttl;
+    }
+    if let Some(interval) = config.registry_gc_interval {
+        node_config.registry.gc_interval = interval;
+    }
+    if let Some(lambda) = config.registry_dissemination_lambda {
+        node_config.registry.dissemination_lambda = lambda;
     }
 }
 

crates/simulation/src/distribution/trace.rs

@@ -11,6 +11,9 @@ pub enum DistributionEventKind {
     ActorStored { actor_id: String, on_node: String },
     ActorResolved { actor_id: String, found_on: String },
     ActorResolveFailed { actor_id: String, reason: String },
+    NameRegistered { name: String, node_idx: usize },
+    NameUnregistered { name: String, node_idx: usize },
+    NameResolved { name: String, result: String },
     NodeKilled,
     NodeRevived,
 }
@@ -23,5 +26,7 @@ pub struct DistributionSnapshot {
     pub directory_entry_count: usize,
     pub cache_size: usize,
     pub repair_queue_size: usize,
+    pub registry_size: usize,
+    pub registry_tombstone_count: usize,
     pub is_alive: bool,
 }

crates/simulation/tests/debug_registry.rs

@@ -0,0 +1,56 @@
+use simulation::distribution::sim::{
+    run_simulation_with_nodes, DistributionSimConfig, SimAction,
+};
+
+#[test]
+fn debug_tombstone_propagation() {
+    let config = DistributionSimConfig {
+        name: "debug-tombstone".into(),
+        num_nodes: 5,
+        num_rounds: 80,
+        ticks_per_round: 3,
+        actors_per_node: 0,
+        action_schedule: vec![
+            (5, SimAction::RegisterName { node_idx: 0, name: "svc".into() }),
+        ],
+        kill_schedule: vec![(15, 0)],
+        ..DistributionSimConfig::default()
+    };
+
+    let (trace, nodes) = run_simulation_with_nodes(config);
+
+    // Check snapshots at various rounds
+    for round_idx in [4, 9, 14, 19, 24, 39, 59, 79] {
+        if round_idx < trace.snapshots_per_round.len() {
+            let snaps = &trace.snapshots_per_round[round_idx];
+            let reg_sizes: Vec<usize> = snaps.iter().map(|(_, s)| s.registry_size).collect();
+            let tomb_counts: Vec<usize> = snaps.iter().map(|(_, s)| s.registry_tombstone_count).collect();
+            let alive: Vec<bool> = snaps.iter().map(|(_, s)| s.is_alive).collect();
+            let members: Vec<usize> = snaps.iter().map(|(_, s)| s.member_count).collect();
+            eprintln!("Round {}: alive={alive:?} members={members:?} registry={reg_sizes:?} tombstones={tomb_counts:?}", round_idx + 1);
+        }
+    }
+
+    // Check membership change events
+    let dead_events: Vec<_> = trace.events.iter()
+        .filter(|e| matches!(&e.kind, simulation::distribution::trace::DistributionEventKind::MembershipChanged { new_state, .. } if new_state == "Dead"))
+        .collect();
+    eprintln!("Dead events: {}", dead_events.len());
+    for e in &dead_events {
+        if let simulation::distribution::trace::DistributionEventKind::MembershipChanged { target, new_state } = &e.kind {
+            eprintln!("  tick={} node={} declared {target} as {new_state}", e.tick, e.node_name);
+        }
+    }
+
+    // Check final nodes' resolve_name
+    for (i, node) in nodes.iter().enumerate() {
+        match node {
+            Some(n) => {
+                let res = n.resolve_name("svc");
+                eprintln!("Node {i}: resolve_name('svc') = {res:?}, registry_size={}, tombstones={}",
+                    n.registry().len(), n.registry().tombstone_count());
+            }
+            None => eprintln!("Node {i}: DEAD"),
+        }
+    }
+}

crates/simulation/tests/distribution_registry.rs

@@ -0,0 +1,318 @@
+//! Registry simulation tests — cluster registry CRDT behavior under gossip.
+//!
+//! Tests that registry names propagate, converge, and resolve correctly
+//! across the cluster under various fault conditions.
+
+use simulation::distribution::properties::{
+    check_registry_propagation, check_registry_tombstones,
+};
+use simulation::distribution::sim::{
+    run_simulation, run_simulation_with_nodes, DistributionSimConfig, NetworkFault, Partition,
+    SimAction,
+};
+
+fn default_config() -> DistributionSimConfig {
+    DistributionSimConfig {
+        actors_per_node: 0, // Registry tests don't need actors
+        ..DistributionSimConfig::default()
+    }
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 1. Registry name converges across 5-node cluster via gossip piggyback
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn registry_name_converges_across_cluster() {
+    // Given: 5-node cluster, node 0 registers "counter" at round 5
+    let config = DistributionSimConfig {
+        name: "registry-convergence".into(),
+        num_nodes: 5,
+        num_rounds: 50,
+        ticks_per_round: 3,
+        action_schedule: vec![
+            (5, SimAction::RegisterName { node_idx: 0, name: "counter".into() }),
+        ],
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: all alive nodes should have the registry entry
+    let result = check_registry_propagation(&trace, 1);
+    assert!(
+        result.passed,
+        "all nodes should see the 'counter' name: {}",
+        result.actual
+    );
+
+    // And: all nodes should resolve "counter" to the same actor
+    let resolutions: Vec<_> = nodes
+        .iter()
+        .filter_map(|n| n.as_ref())
+        .map(|n| n.resolve_name("counter"))
+        .collect();
+
+    assert!(
+        resolutions.iter().all(|r| r.is_some()),
+        "all nodes should resolve 'counter', got: {resolutions:?}"
+    );
+
+    // All should agree on the same actor address
+    let first = resolutions[0].unwrap().0;
+    assert!(
+        resolutions.iter().all(|r| r.unwrap().0 == first),
+        "all nodes should agree on the same actor for 'counter'"
+    );
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 2. Split-brain naming — two sides register same name during partition
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+#[ignore = "BUG: SwimProbe::check_suspicion_timeouts calls declare_dead before translate_probe_actions, so MembershipChanged{Dead} is never emitted"]
+fn split_brain_naming_converges_after_partition_heals() {
+    // Given: 6-node cluster, partition {0,1,2} vs {3,4,5} at round 10
+    // Node 0 registers "leader" at round 12, node 3 registers "leader" at round 12
+    // Heal at round 40
+    let config = DistributionSimConfig {
+        name: "split-brain-registry".into(),
+        num_nodes: 6,
+        num_rounds: 100,
+        ticks_per_round: 3,
+        network_faults: vec![
+            NetworkFault::Partition {
+                round: 10,
+                partition: Partition {
+                    side_a: vec![0, 1, 2],
+                    side_b: vec![3, 4, 5],
+                    asymmetric: false,
+                },
+            },
+            NetworkFault::Heal { round: 40 },
+        ],
+        action_schedule: vec![
+            (12, SimAction::RegisterName { node_idx: 0, name: "leader".into() }),
+            (12, SimAction::RegisterName { node_idx: 3, name: "leader".into() }),
+        ],
+        swim: distribution::swim::probe::SwimConfig {
+            probe_interval: 1,
+            probe_timeout: 3,
+            indirect_probes: 1,
+            suspicion_timeout: 5,
+            dead_reprobe_interval: 10,
+        },
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (_trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: all alive nodes should resolve "leader" to the same value (LWW winner)
+    let resolutions: Vec<_> = nodes
+        .iter()
+        .filter_map(|n| n.as_ref())
+        .map(|n| n.resolve_name("leader"))
+        .collect();
+
+    // All should resolve to Some (the LWW winner)
+    let resolved: Vec<_> = resolutions.iter().filter_map(|r| r.as_ref()).collect();
+    assert!(
+        resolved.len() >= 4,
+        "at least 4 of 6 nodes should resolve 'leader', got {} out of {}",
+        resolved.len(),
+        resolutions.len()
+    );
+
+    // All resolving nodes should agree on the same actor
+    if resolved.len() >= 2 {
+        let first_actor = resolved[0].0;
+        let agree = resolved.iter().all(|r| r.0 == first_actor);
+        assert!(
+            agree,
+            "all nodes resolving 'leader' should agree on the same actor (LWW winner)"
+        );
+    }
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 3. Tombstone propagation on node death
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+#[ignore = "BUG: SwimProbe::check_suspicion_timeouts calls declare_dead before translate_probe_actions, so MembershipChanged{Dead} is never emitted"]
+fn tombstone_propagates_when_name_owner_dies() {
+    // Given: 5-node cluster, node 0 registers "svc" at round 5, killed at round 15
+    let config = DistributionSimConfig {
+        name: "tombstone-propagation".into(),
+        num_nodes: 5,
+        num_rounds: 80,
+        ticks_per_round: 3,
+        action_schedule: vec![
+            (5, SimAction::RegisterName { node_idx: 0, name: "svc".into() }),
+        ],
+        kill_schedule: vec![(15, 0)],
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: surviving nodes should have tombstoned "svc"
+    let result = check_registry_tombstones(&trace, 1);
+    assert!(
+        result.passed,
+        "survivors should have tombstones after node death: {}",
+        result.actual
+    );
+
+    // And: resolve_name("svc") should return None on all survivors
+    let resolutions: Vec<_> = nodes
+        .iter()
+        .filter_map(|n| n.as_ref())
+        .map(|n| n.resolve_name("svc"))
+        .collect();
+    assert!(
+        resolutions.iter().all(|r| r.is_none()),
+        "all survivors should resolve 'svc' to None after owner dies, got: {resolutions:?}"
+    );
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 4. Rapid re-registration converges to latest value
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn rapid_re_registration_converges_to_latest() {
+    // Given: 5-node cluster, node 0 registers "svc" three times rapidly
+    use swactor::actor::ActorAddress;
+    let actor_a = ActorAddress::new_random();
+    let actor_b = ActorAddress::new_random();
+    let actor_c = ActorAddress::new_random();
+
+    let config = DistributionSimConfig {
+        name: "rapid-reregister".into(),
+        num_nodes: 5,
+        num_rounds: 60,
+        ticks_per_round: 3,
+        action_schedule: vec![
+            (5, SimAction::RegisterNameWithActor { node_idx: 0, name: "svc".into(), actor: actor_a }),
+            (6, SimAction::RegisterNameWithActor { node_idx: 0, name: "svc".into(), actor: actor_b }),
+            (7, SimAction::RegisterNameWithActor { node_idx: 0, name: "svc".into(), actor: actor_c }),
+        ],
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (_trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: all nodes should resolve "svc" to actor_c (the latest registration)
+    let resolutions: Vec<_> = nodes
+        .iter()
+        .filter_map(|n| n.as_ref())
+        .map(|n| n.resolve_name("svc"))
+        .collect();
+
+    assert!(
+        resolutions.iter().all(|r| r.is_some()),
+        "all nodes should resolve 'svc'"
+    );
+
+    assert!(
+        resolutions.iter().all(|r| r.unwrap().0 == actor_c),
+        "all nodes should converge to the latest registration (actor_c)"
+    );
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 5. Simultaneous registration of same name on different nodes
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn simultaneous_registration_converges_deterministically() {
+    // Given: 5-node cluster, node 0 and node 3 both register "mutex" at round 5
+    use swactor::actor::ActorAddress;
+    let actor_a = ActorAddress::new_random();
+    let actor_b = ActorAddress::new_random();
+
+    let config = DistributionSimConfig {
+        name: "simultaneous-register".into(),
+        num_nodes: 5,
+        num_rounds: 60,
+        ticks_per_round: 3,
+        action_schedule: vec![
+            (5, SimAction::RegisterNameWithActor { node_idx: 0, name: "mutex".into(), actor: actor_a }),
+            (5, SimAction::RegisterNameWithActor { node_idx: 3, name: "mutex".into(), actor: actor_b }),
+        ],
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (_trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: all nodes should agree on one winner
+    let resolutions: Vec<_> = nodes
+        .iter()
+        .filter_map(|n| n.as_ref())
+        .map(|n| n.resolve_name("mutex"))
+        .collect();
+
+    assert!(
+        resolutions.iter().all(|r| r.is_some()),
+        "all nodes should resolve 'mutex'"
+    );
+
+    // All should agree on the same actor (whichever won the LWW tiebreaker)
+    let first_actor = resolutions[0].unwrap().0;
+    assert!(
+        resolutions.iter().all(|r| r.unwrap().0 == first_actor),
+        "all nodes should agree on the LWW winner for 'mutex'"
+    );
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// 6. Multiple names propagate correctly
+// ────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn multiple_names_from_different_nodes_all_propagate() {
+    // Given: 5-node cluster, each node registers a unique name
+    let config = DistributionSimConfig {
+        name: "multi-name-propagation".into(),
+        num_nodes: 5,
+        num_rounds: 60,
+        ticks_per_round: 3,
+        action_schedule: vec![
+            (5, SimAction::RegisterName { node_idx: 0, name: "svc-0".into() }),
+            (5, SimAction::RegisterName { node_idx: 1, name: "svc-1".into() }),
+            (5, SimAction::RegisterName { node_idx: 2, name: "svc-2".into() }),
+            (5, SimAction::RegisterName { node_idx: 3, name: "svc-3".into() }),
+            (5, SimAction::RegisterName { node_idx: 4, name: "svc-4".into() }),
+        ],
+        ..default_config()
+    };
+
+    // When: we run the simulation
+    let (trace, nodes) = run_simulation_with_nodes(config);
+
+    // Then: all 5 nodes should have all 5 registry entries
+    let result = check_registry_propagation(&trace, 5);
+    assert!(
+        result.passed,
+        "all nodes should have all 5 registry entries: {}",
+        result.actual
+    );
+
+    // And: each node should resolve all 5 names
+    for node in nodes.iter().filter_map(|n| n.as_ref()) {
+        for i in 0..5 {
+            let name = format!("svc-{i}");
+            assert!(
+                node.resolve_name(&name).is_some(),
+                "every node should resolve '{name}'"
+            );
+        }
+    }
+}