From ab3936adece2d06de622d5dd3399a218bd7c18c6 Mon Sep 17 00:00:00 2001
From: Cursor Agent <cursoragent@cursor.com>
Date: Thu, 1 Oct 2026 08:24:22 +0000
Subject: [PATCH] [qec] Share Stim reset assembly in the emitter module

Both circuit builders call emit_reset_tick for the prepare-R line.
Callers still choose the id list: layout order for single-block memory,
sorted unique ids for lattice surgery. Checked-in Stim gold stays
byte-identical.

Issue 473 stays open. Headers and observable assembly stay in the builders.

Co-authored-by: Arnab Ghosh <ag2583@cornell.edu>
---
 quon_qec/src/experiment.rs           | 12 ++++--------
 quon_qec/src/experiment/stim_emit.rs | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/quon_qec/src/experiment.rs b/quon_qec/src/experiment.rs
index 5ffe2b6..4447190 100644
--- a/quon_qec/src/experiment.rs
+++ b/quon_qec/src/experiment.rs
@@ -493,11 +493,11 @@ fn emit_stim_single_block_memory(expanded: &ExpandedWorkload) -> Result<String,
     }
 
     // Prepare |0…0⟩ then optional data H for X-init / X-memory (|+⟩^n).
-    out.push('R');
+    let mut reset_ids = Vec::with_capacity(block.atoms.len());
     for atom in &block.atoms {
-        out.push_str(&format!(" {}", atom.0));
+        reset_ids.push(atom.0);
     }
-    out.push_str("\nTICK\n");
+    stim_emit::emit_reset_tick(&mut out, &reset_ids);
 
     let z_check_indices: Vec<usize> = block
         .stabilizers
@@ -673,11 +673,7 @@ fn emit_stim_lattice_surgery_cx(expanded: &ExpandedWorkload) -> Result<String, E
         .collect();
     all_atoms.sort_unstable();
     all_atoms.dedup();
-    out.push('R');
-    for id in &all_atoms {
-        out.push_str(&format!(" {id}"));
-    }
-    out.push_str("\nTICK\n");
+    stim_emit::emit_reset_tick(&mut out, &all_atoms);
 
     // Round kinds append through [`stim_emit::StimRoundEmitter`]. Byproduct
     // handles and deferred measure-logical rounds come back out for observable
diff --git a/quon_qec/src/experiment/stim_emit.rs b/quon_qec/src/experiment/stim_emit.rs
index f0625a9..3968259 100644
--- a/quon_qec/src/experiment/stim_emit.rs
+++ b/quon_qec/src/experiment/stim_emit.rs
@@ -8,6 +8,9 @@
 //! Lattice surgery calls [`StimRoundEmitter::emit`]. Single-block memory calls
 //! [`StimRoundEmitter::emit_single_block`] on the same registry. A new round
 //! kind is a new impl plus one arm in [`lattice_round_emitter`].
+//!
+//! Both builders share [`emit_reset_tick`] for the prepare-`R` / `TICK` line.
+//! Headers and observable assembly stay in the builders.
 
 use std::collections::HashMap;
 
@@ -19,6 +22,18 @@ use crate::workload::LogicalBasis;
 
 use super::{ExperimentError, emit_local_ops, emit_round_body, logical_observable_atoms};
 
+/// Write `R <ids>\nTICK\n` in caller order.
+///
+/// Single-block memory passes layout order. Lattice surgery passes the sorted
+/// unique id list. This function does not reorder.
+pub(crate) fn emit_reset_tick(out: &mut String, atom_ids: &[u32]) {
+    out.push('R');
+    for id in atom_ids {
+        out.push_str(&format!(" {id}"));
+    }
+    out.push_str("\nTICK\n");
+}
+
 /// Shared Stim state for one lattice-surgery circuit.
 ///
 /// Round impls append instructions and record byproduct handles. Observable
@@ -671,4 +686,14 @@ mod tests {
         assert!(ctx.measure_logical.is_none());
         assert_eq!(ctx.memory_round_i, 0);
     }
+
+    #[test]
+    fn reset_tick_keeps_caller_order() {
+        let mut out = String::new();
+        emit_reset_tick(&mut out, &[4, 0, 4]);
+        assert_eq!(out, "R 4 0 4\nTICK\n");
+        let mut empty = String::new();
+        emit_reset_tick(&mut empty, &[]);
+        assert_eq!(empty, "R\nTICK\n");
+    }
 }