add write frame cursor offset as well

Author: stringhandler

src/bit_machine/mod.rs

@@ -277,8 +277,11 @@ impl BitMachine {
         }
 
         'main_loop: loop {
-            // Make a copy of the input frame to give to the tracker.
+            // Capture read and write frames before the node action, to give to the tracker.
+            // The read frame cursor is where the node's input begins.
+            // The write frame cursor is where the node's output begins.
             let input_frame = self.read.last().map(Frame::shallow_copy);
+            let output_frame = self.write.last().map(Frame::shallow_copy);
             let mut jet_result = Ok(());
 
             match ip.inner() {
@@ -393,9 +396,8 @@ impl BitMachine {
                 let output = match (ip.inner(), &jet_result) {
                     (node::Inner::Unit | node::Inner::Iden | node::Inner::Witness(_), _)
                     | (node::Inner::Jet(_), Ok(_)) => NodeOutput::Success(
-                        self.write
-                            .last()
-                            .map(|r| r.as_bit_iter(&self.data))
+                        output_frame
+                            .map(|frame| frame.as_bit_iter_from_cursor(&self.data))
                             .unwrap_or(crate::BitIter::from([].iter().copied())),
                     ),
                     (node::Inner::Jet(_), Err(_)) => NodeOutput::JetFailed,