tests: cover ignored EOS at the output limit

A request with ignore_eos keeps generating past end-of-sequence tokens, so its
last sampled token can be an EOS id even though it finished on the output
limit. Assert that the terminal event reports the length reason and the
output-limit termination.

Validation: the new case fails on the unfixed runtime at the terminal-event
assertion (reason "stop", termination Eos) in the release library test build.

Design-Signed-Off-By: Hermes Agent (DeepSeek V4.1 Flash); design-review=2d93

Author: mark-yong

helios/src/server/runtime/phase_tests.rs

@@ -715,6 +715,39 @@ fn exact_system_and_prompt_checkpoints_publish_only_after_snapshot_completion()
     assert_eq!((metrics.prefill_tokens, metrics.generated_tokens), (13, 3));
 }
 
+#[test]
+fn ignored_eos_at_the_output_limit_finishes_for_length() {
+    let fixture = Fixture::new();
+    let (sender, receiver) = mpsc::channel();
+    let (mut incoming, mut generation) = fixture.incoming(vec![0], 2);
+    incoming.prompt.ignore_eos = true;
+    sender.send(vec![incoming]).unwrap();
+    let mut worker = fixture.worker(receiver);
+    assert_eq!(worker.admit().unwrap(), ControlFlow::Continue(true));
+    advance(&mut worker, GraphKind::Init, 1, None);
+    advance(&mut worker, GraphKind::Prefill, 2, Some(5));
+    advance(&mut worker, GraphKind::Snapshot, 3, None);
+    advance(&mut worker, GraphKind::Decode, 4, Some(5));
+    advance(&mut worker, GraphKind::Snapshot, 5, None);
+    assert!(worker.publish().unwrap());
+    let mut finished = Vec::new();
+    while let Ok(event) = generation.events.try_recv() {
+        if let GenerationEvent::Finished {
+            generated_tokens,
+            reason,
+            termination,
+            ..
+        } = event
+        {
+            finished.push((generated_tokens, reason, termination));
+        }
+    }
+    assert_eq!(
+        finished,
+        vec![(2, "length", crate::output::Termination::OutputLimit)]
+    );
+}
+
 #[test]
 fn disabled_host_store_preserves_decode_prefix_reuse_and_cancellation() {
     let fixture = Fixture::new();