From 49887a544132d27003ad92bc0354e33eaf4474f8 Mon Sep 17 00:00:00 2001
From: Aniket Dalvi <aniksd@amazon.com>
Date: Thu, 14 May 2026 11:49:58 -0700
Subject: [PATCH] fix(interpreter): Skip rvalue evaluation for MCM-dependent
 assignments in non-simulating contexts

When a classical assignment has an MCM-dependent rvalue and the context
has no active simulation paths (e.g., Qiskit circuit-building contexts),
skip evaluating the rvalue and just propagate MCM-dependency. This
prevents NameError when measurement results have no stored runtime value.
---
 .../default_simulator/openqasm/interpreter.py |  7 ++++++
 .../braket/default_simulator/test_mcm.py      | 23 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/src/braket/default_simulator/openqasm/interpreter.py b/src/braket/default_simulator/openqasm/interpreter.py
index c40d16c9..6e539da5 100644
--- a/src/braket/default_simulator/openqasm/interpreter.py
+++ b/src/braket/default_simulator/openqasm/interpreter.py
@@ -597,6 +597,13 @@ def _execute_classical_assignment(self, node: ClassicalAssignment) -> None:
         lvalue_name = get_identifier_name(node.lvalue)
         if self.context.get_const(lvalue_name):
             raise TypeError(f"Cannot update const value {lvalue_name}")
+        if (
+            self.context.supports_midcircuit_measurement
+            and not self.context.active_paths
+            and self.context.is_mcm_dependent(node.rvalue)
+        ):
+            self.context.track_mcm_dependency(lvalue_name, node.rvalue)
+            return
         rvalue = self.visit(
             node.rvalue
             if node.op == getattr(AssignmentOperator, "=")
diff --git a/test/unit_tests/braket/default_simulator/test_mcm.py b/test/unit_tests/braket/default_simulator/test_mcm.py
index 71429c81..2eb813aa 100644
--- a/test/unit_tests/braket/default_simulator/test_mcm.py
+++ b/test/unit_tests/braket/default_simulator/test_mcm.py
@@ -4976,3 +4976,26 @@ def test_flat_context_preserves_mcm_while_loop(self):
             "}"
         )
         assert Interpreter(context=FlatProgramContext()).run(qasm).circuit == qasm
+
+    def test_flat_context_mcm_propagation_through_assignment(self):
+        """MCM dependency propagates through classical assignment without crashing.
+
+        When a measurement result is assigned to an intermediate variable and then
+        used in a condition, the interpreter should skip rvalue evaluation (since
+        non-simulating contexts have no runtime values) and just propagate the
+        MCM-dependency so the condition is correctly routed to evaluate_condition.
+        """
+        qasm = (
+            "OPENQASM 3.0;\n"
+            "qubit[2] q;\n"
+            "bit mcm;\n"
+            "bit tmp;\n"
+            "tmp = measure q[0];\n"
+            "mcm = tmp;\n"
+            "if (mcm == 1) {\n"
+            "    x q[1];\n"
+            "}"
+        )
+        result = Interpreter(context=FlatProgramContext()).run(qasm).circuit
+        assert "if (mcm == 1)" in result
+        assert "x q[1]" in result