Land community PR #34: sequence_vec benchmark + observe-path stack-safety regression test

Cargo.toml

@@ -65,3 +65,7 @@ harness = false
 [[bench]]
 name = "f_perf"
 harness = false
+
+[[bench]]
+name = "sequence_vec"
+harness = false

benches/sequence_vec.rs

@@ -0,0 +1,29 @@
+//! Benchmark for large sequences of simple observations.
+
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use fugue::*;
+use rand::rngs::StdRng;
+use rand::SeedableRng;
+
+fn benchmark_stack_overflow_model(c: &mut Criterion) {
+    let n = 1_000usize;
+
+    c.bench_function("stack_overflow_model/sequence_vec", |b| {
+        b.iter(|| {
+            let models: Vec<Model<bool>> = (0..n)
+                .map(|i| sample(addr!("coin", i), Bernoulli::new(0.5).unwrap()))
+                .collect();
+            let model = sequence_vec(models);
+            let mut rng = StdRng::seed_from_u64(42);
+            let handler = runtime::interpreters::PriorHandler {
+                rng: &mut rng,
+                trace: runtime::trace::Trace::default(),
+            };
+            let (result, _trace) = runtime::handler::run(handler, model);
+            black_box(result.len());
+        })
+    });
+}
+
+criterion_group!(stack_overflow_benches, benchmark_stack_overflow_model);
+criterion_main!(stack_overflow_benches);

src/runtime/handler.rs

@@ -287,4 +287,30 @@ mod tests {
             .join()
             .expect("deep model interpretation overflowed the stack");
     }
+
+    // Companion regression from PR #34: the same stack-safety guarantee through
+    // the `sequence_vec` + `observe` path (the deep test above covers
+    // sample+bind). 100k observations interpreted through `sequence_vec` must
+    // complete without overflowing the stack.
+    #[test]
+    fn run_handles_large_observe_sequence() {
+        use crate::core::model::{observe, sequence_vec};
+
+        let n = 100_000usize;
+        let models: Vec<Model<()>> = (0..n)
+            .map(|i| observe(addr!("obs", i), Bernoulli::new(0.5).unwrap(), true))
+            .collect();
+        let model = sequence_vec(models).map(|_| ());
+
+        let mut rng = StdRng::seed_from_u64(123);
+        let (_a, trace) = crate::runtime::handler::run(
+            PriorHandler {
+                rng: &mut rng,
+                trace: Trace::default(),
+            },
+            model,
+        );
+
+        assert!(trace.log_likelihood.is_finite());
+    }
 }