feat: add initial

Signed-off-by: kjuulh <contact@kjuulh.io>

todos/SQ-019-virtual-network.md

@@ -0,0 +1,45 @@
+# SQ-019: Virtual Network for Simulation
+
+**Status:** `[ ] TODO`
+**Blocked by:** SQ-003
+**Priority:** Medium
+
+## Description
+
+Virtual network layer for multi-node simulation testing. Enables partition, latency, and packet drop injection.
+
+## Files to Create/Modify
+
+- `crates/sq-sim/src/network.rs` - VirtualNetwork with message queues and fault injection
+
+## VirtualNetwork API
+
+```rust
+pub struct VirtualNetwork {
+    queues: HashMap<(NodeId, NodeId), VecDeque<Vec<u8>>>,
+    partitions: HashSet<(NodeId, NodeId)>,
+    latency: Option<(Duration, Duration)>,  // min, max
+    drop_probability: f64,
+}
+
+impl VirtualNetwork {
+    pub fn new() -> Self;
+    pub fn partition(&mut self, a: NodeId, b: NodeId);
+    pub fn heal(&mut self, a: NodeId, b: NodeId);
+    pub fn heal_all(&mut self);
+    pub fn set_latency(&mut self, min: Duration, max: Duration);
+    pub fn set_drop_probability(&mut self, prob: f64);
+    pub async fn send(&self, from: NodeId, to: NodeId, msg: Vec<u8>) -> Result<()>;
+    pub async fn recv(&self, node: NodeId) -> Result<(NodeId, Vec<u8>)>;
+    pub fn deliver_pending(&mut self);  // Process queued messages
+}
+```
+
+## Acceptance Criteria
+
+- [ ] Two virtual nodes exchange messages successfully
+- [ ] Partition: messages from A to B are dropped
+- [ ] Heal: messages resume flowing after heal
+- [ ] Latency injection: messages are delayed
+- [ ] Drop probability: some messages are randomly dropped
+- [ ] Bidirectional partition: neither direction works