processor: add exact continuation stack limit regression test

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Replaced unsound `ptr::read` with safe unbox in panic recovery, removing UB from potential double-drop ([#2934](https://github.com/0xMiden/miden-vm/pull/2934)).
 - Reverted `InvokeKind::ProcRef` back to `InvokeKind::Exec` in `visit_mut_procref` and added an explanatory comment (#2893).
 - Fixed the release dry-run publish cycle between `miden-air` and `miden-ace-codegen`, and preserved leaf-only DAG imports with explicit snapshots ([#2931](https://github.com/0xMiden/miden-vm/pull/2931)).
+- Added regression coverage for the exact `max_num_continuations` continuation-stack boundary ([#2995](https://github.com/0xMiden/miden-vm/pull/2995)).
 
 #### Changes
 

processor/src/fast/tests/mod.rs

@@ -611,6 +611,33 @@ fn test_continuation_stack_limit_exceeded() {
     assert_matches!(err, ExecutionError::Internal(msg) if msg.contains("continuation stack"));
 }
 
+/// Tests that a continuation stack size exactly equal to `max_num_continuations` succeeds.
+#[test]
+fn test_continuation_stack_limit_exactly_max_continuations_succeeds() {
+    let mut host = DefaultHost::default();
+
+    let program = {
+        let mut forest = MastForest::new();
+
+        let leaf_id = BasicBlockNodeBuilder::new(vec![Operation::Noop], Vec::new())
+            .add_to_forest(&mut forest)
+            .unwrap();
+
+        let root = JoinNodeBuilder::new([leaf_id, leaf_id]).add_to_forest(&mut forest).unwrap();
+        forest.make_root(root);
+        Program::new(forest.into(), root)
+    };
+
+    // A single join peaks at three continuations after the join start step:
+    // FinishJoin(root), StartNode(second), StartNode(first).
+    let options = ExecutionOptions::default().with_max_num_continuations(3);
+
+    let processor =
+        FastProcessor::new_with_options(StackInputs::default(), AdviceInputs::default(), options);
+
+    processor.execute_sync(&program, &mut host).unwrap();
+}
+
 // TEST HELPERS
 // -----------------------------------------------------------------------------------------------