diff --git a/src/runtime2/inbox.rs b/src/runtime2/inbox.rs
index c71ec0d15da177c50795ef34949e878eafb347ba..db5c94535cae7f96ccc86ca0bc81faa4b00df51c 100644
--- a/src/runtime2/inbox.rs
+++ b/src/runtime2/inbox.rs
@@ -23,13 +23,19 @@ use super::global_store::ConnectorId;
 /// A message prepared by a connector. Waiting to be picked up by the runtime to
 /// be sent to another connector.
 #[derive(Clone)]
-pub struct OutgoingMessage {
+pub struct OutgoingDataMessage {
     pub sending_port: PortIdLocal,
     pub sender_prev_branch_id: BranchId, // may be invalid, implying no prev branch id
     pub sender_cur_branch_id: BranchId, // always valid
     pub message: ValueGroup,
 }
 
+pub enum OutgoingMessage {
+    Data(OutgoingDataMessage),
+    Sync(SyncMessage),
+    Solution(SolutionMessage),
+}
+
 /// A message that has been delivered (after being imbued with the receiving
 /// port by the scheduler) to a connector.
 #[derive(Clone)]
@@ -42,12 +48,14 @@ pub struct DataMessage {
     pub message: ValueGroup,
 }
 
+#[derive(Clone)]
 pub enum SyncBranchConstraint {
     SilentPort(PortIdLocal),
     BranchNumber(BranchId),
     PortMapping(PortIdLocal, BranchId),
 }
 
+#[derive(Clone)]
 pub struct SyncConnectorSolution {
     pub connector_id: ConnectorId,
     pub terminating_branch_id: BranchId,
@@ -55,11 +63,13 @@ pub struct SyncConnectorSolution {
     pub final_port_mapping: Vec<(PortIdLocal, BranchId)>
 }
 
+#[derive(Clone)]
 pub struct SyncConnectorConstraints {
     pub connector_id: ConnectorId,
     pub constraints: Vec<SyncBranchConstraint>,
 }
 
+#[derive(Clone)]
 pub struct SyncMessage {
     pub local_solutions: Vec<SyncConnectorSolution>,
     pub constraints: Vec<SyncConnectorConstraints>,
@@ -103,7 +113,7 @@ impl SyncMessage {
         if self.has_local_solution_for(connector_id) {
             return self.check_constraint(connector_id, constraint);
         } else {
-            self.add_constraint(connector_id);
+            self.add_constraint(connector_id, constraint);
             return Ok(true);
         }
     }
@@ -175,6 +185,10 @@ impl SyncMessage {
     }
 }
 
+pub struct SolutionMessage {
+    pub local_solutions: Vec<(ConnectorId, BranchId)>,
+}
+
 /// A control message. These might be sent by the scheduler to notify eachother
 /// of asynchronous state changes.
 pub struct ControlMessage {
@@ -194,6 +208,7 @@ pub enum ControlMessageVariant {
 pub enum Message {
     Data(DataMessage),          // data message, handled by connector
     Sync(SyncMessage),          // sync message, handled by both connector/scheduler
+    Solution(SolutionMessage),  // solution message, finishing a sync round
     Control(ControlMessage),    // control message, handled by scheduler
     Ping,                       // ping message, intentionally waking up a connector (used for native connectors)
 }