feat(incremental): a scheduler runs sub-circuits on a worker pool; the aggregate and grid stages placed on two units

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

crates/zset/src/edge.rs

@@ -144,6 +144,7 @@ pub struct EdgeSink<K, C, P> {
     waiting: Delta<K>,
     owes_correction: bool,
     closed: bool,
+    traffic: u64,
 }
 
 impl<K: Ord + Clone, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSink<K, C, P> {
@@ -169,6 +170,7 @@ impl<K: Ord + Clone, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSink<K, C, P> {
             },
             owes_correction: false,
             closed: false,
+            traffic: 0,
         }
     }
 
@@ -179,6 +181,11 @@ impl<K: Ord + Clone, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSink<K, C, P> {
         }
     }
 
+    /// Frames sent and requests read so far: a host sees progress when it moves.
+    pub fn traffic(&self) -> u64 {
+        self.traffic
+    }
+
     /// Whether any committed command has not been sent.
     pub fn backlog(&self) -> bool {
         self.waiting.to > self.waiting.from || self.owes_correction
@@ -217,6 +224,7 @@ impl<K: Ord + Clone, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSink<K, C, P> {
         while !self.closed {
             match self.pipe.try_recv() {
                 Ok(wire) => {
+                    self.traffic += 1;
                     if let Ok(Frame::Request(_)) = self.codec.decode(wire) {
                         self.owes_correction = true;
                     }
@@ -241,6 +249,7 @@ impl<K: Ord + Clone, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSink<K, C, P> {
         };
         match self.pipe.try_send(self.codec.encode(&frame)) {
             Ok(()) => {
+                self.traffic += 1;
                 self.owes_correction = false;
                 self.waiting = Delta {
                     epoch: self.epoch,
@@ -275,6 +284,7 @@ pub struct EdgeSource<K, C, P> {
     stale: bool,
     asked: bool,
     closed: bool,
+    traffic: u64,
 }
 
 impl<K: Ord + Clone + Send + 'static, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSource<K, C, P> {
@@ -291,6 +301,7 @@ impl<K: Ord + Clone + Send + 'static, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSou
             stale: true,
             asked: false,
             closed: false,
+            traffic: 0,
         }
     }
 
@@ -302,6 +313,11 @@ impl<K: Ord + Clone + Send + 'static, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSou
         })
     }
 
+    /// Frames read and requests sent so far: a host sees progress when it moves.
+    pub fn traffic(&self) -> u64 {
+        self.traffic
+    }
+
     /// Whether a correction is wanted and has not arrived.
     pub fn stale(&self) -> bool {
         self.stale
@@ -326,6 +342,7 @@ impl<K: Ord + Clone + Send + 'static, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSou
             match self.pipe.try_recv() {
                 Ok(wire) => {
                     read += 1;
+                    self.traffic += 1;
                     match self.codec.decode(wire) {
                         Ok(Frame::Delta(d)) => self.on_delta(circuit, d),
                         Ok(Frame::Correction(c)) => self.on_correction(circuit, c),
@@ -396,7 +413,10 @@ impl<K: Ord + Clone + Send + 'static, C: EdgeCodec<K>, P: Pipe<C::Wire>> EdgeSou
             .codec
             .encode(&Frame::Request(Request { have: self.stamp() }));
         match self.pipe.try_send(wire) {
-            Ok(()) => self.asked = true,
+            Ok(()) => {
+                self.asked = true;
+                self.traffic += 1;
+            }
             Err(Refused::Full(_)) => {}
             Err(Refused::Closed) => self.closed = true,
         }

crates/zset/tests/edge.rs

@@ -702,3 +702,24 @@ fn a_circuit_on_each_of_two_threads_equals_one_circuit() {
         "[threads] the consumer after the producer thread finishes"
     );
 }
+
+#[test]
+fn a_poll_reads_at_most_the_frames_it_is_given() {
+    let (a, mut b) = channel_pipes::<Frame<u8>>(8);
+    let mut c = Circuit::new();
+    let (i, _) = c.input::<u8>();
+    let mut src = EdgeSource::new(Direct, a, i);
+    for through in 0..3 {
+        let target = Z::new();
+        let frame = Frame::Correction(Correction {
+            epoch: 1,
+            through,
+            target,
+        });
+        b.try_send(frame).unwrap();
+    }
+    assert_eq!(src.poll(&mut c, 2), 2, "[budget] two of three");
+    assert_eq!(src.stamp(), Some(Stamp { epoch: 1, seq: 1 }));
+    assert_eq!(src.poll(&mut c, 2), 1, "[budget] the rest");
+    assert_eq!(src.stamp(), Some(Stamp { epoch: 1, seq: 2 }));
+}