feat: wire bucket identities through driver outputs

src/sim/engine.rs

@@ -91,11 +91,24 @@ mod tests {
         q.schedule(
             2.0,
             Event::BatchTick {
+                bucket: 0,
                 instance: 0 as InstanceId,
             },
         );
-        q.schedule(1.0, Event::BatchTick { instance: 1 });
-        q.schedule(1.5, Event::BatchTick { instance: 2 });
+        q.schedule(
+            1.0,
+            Event::BatchTick {
+                bucket: 0,
+                instance: 1,
+            },
+        );
+        q.schedule(
+            1.5,
+            Event::BatchTick {
+                bucket: 0,
+                instance: 2,
+            },
+        );
         let (t1, _) = q.pop().unwrap();
         let (t2, _) = q.pop().unwrap();
         let (t3, _) = q.pop().unwrap();
@@ -107,12 +120,24 @@ mod tests {
     #[test]
     fn equal_time_fifo() {
         let mut q = EventQueue::new();
-        q.schedule(1.0, Event::BatchTick { instance: 7 });
-        q.schedule(1.0, Event::BatchTick { instance: 8 });
+        q.schedule(
+            1.0,
+            Event::BatchTick {
+                bucket: 0,
+                instance: 7,
+            },
+        );
+        q.schedule(
+            1.0,
+            Event::BatchTick {
+                bucket: 1,
+                instance: 8,
+            },
+        );
         let (_, e1) = q.pop().unwrap();
         let (_, e2) = q.pop().unwrap();
         match (e1, e2) {
-            (Event::BatchTick { instance: a }, Event::BatchTick { instance: b }) => {
+            (Event::BatchTick { instance: a, .. }, Event::BatchTick { instance: b, .. }) => {
                 assert_eq!(a, 7);
                 assert_eq!(b, 8);
             }

src/sim/events.rs

@@ -1,5 +1,6 @@
 //! Event types for the discrete-event engine.
 
+use crate::router::BucketId;
 use crate::types::{InstanceId, ReqId};
 
 #[derive(Debug)]
@@ -7,7 +8,10 @@ pub enum Event {
     /// New trace request arrives at the cluster router.
     Arrival { req_id: ReqId },
     /// Per-instance scheduler tick (continuous batching).
-    BatchTick { instance: InstanceId },
+    BatchTick {
+        bucket: BucketId,
+        instance: InstanceId,
+    },
     /// Periodic time-series sample of all instances.
     Sample,
     /// Stop the simulation early (used internally).