diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index cdae2e037a59..c81e7d84b4bf 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -101,6 +101,23 @@ jobs:
         # re-download, keeping the persisted cache small and fast to restore.
         run: uv cache prune --ci
 
+      - name: Run merge-sensitive provider contracts
+        if: matrix.slice.index == 1
+        # Keep provider concurrency and client-lifecycle contracts visible
+        # outside the duration-balanced file shards.
+        run: |
+          source .venv/bin/activate
+          python -m pytest -q --tb=short \
+            tests/agent/test_relay_llm.py::test_anthropic_stream_callbacks_do_not_reenter_captured_context \
+            tests/agent/test_relay_llm.py::test_explicit_stream_close_surfaces_provider_close_failure \
+            tests/run_agent/test_streaming.py::TestAnthropicStreamCallbacks::test_anthropic_sdk_stream_runs_through_relay_managed_execution \
+            tests/run_agent/test_request_client_reuse_abort_races.py::test_relay_managed_close_failure_poisons_request_client
+        env:
+          ANTHROPIC_API_KEY: ""
+          OPENROUTER_API_KEY: ""
+          OPENAI_API_KEY: ""
+          NOUS_API_KEY: ""
+
       - name: Run tests (slice ${{ matrix.slice.index }}/${{ inputs.slice_count }})
         # Per-file isolation via scripts/run_tests.sh: each test file runs
         # in its own freshly-spawned `python -m pytest <file>` subprocess
diff --git a/tests/run_agent/test_request_client_reuse_abort_races.py b/tests/run_agent/test_request_client_reuse_abort_races.py
index 73a9c41887cc..76b3bc49946d 100644
--- a/tests/run_agent/test_request_client_reuse_abort_races.py
+++ b/tests/run_agent/test_request_client_reuse_abort_races.py
@@ -25,7 +25,12 @@ Invariants pinned here:
 4. ``run_codex_stream``'s finally must poison the reuse slot when
    ``event_stream.close()`` fails; otherwise a failed close caches the
    client with a connection still checked out of the pool.
+
+5. Relay's managed stream wrapper must preserve the same close failure and
+   request-client identity rather than masking the signal used to poison the
+   slot.
 """
+from contextlib import contextmanager
 import threading
 import time
 from types import SimpleNamespace
@@ -49,6 +54,33 @@ def _make_agent():
     return agent
 
 
+@contextmanager
+def _managed_relay_turn(agent, tmp_path, monkeypatch):
+    pytest.importorskip("nemo_relay")
+    from agent import relay_runtime
+
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "profile"))
+    relay_runtime._reset_for_tests()
+    lease = relay_runtime.SESSION_COORDINATOR.acquire_conversation(
+        profile_key=relay_runtime.current_profile_key(),
+        session_id=agent.session_id,
+        platform="cli",
+    )
+    turn = relay_runtime.SESSION_COORDINATOR.begin_turn(
+        lease,
+        turn_id="request-client-reuse-turn",
+        task_id="request-client-reuse-task",
+    )
+    lease.host.retain_managed_execution("test.request_client_reuse")
+    try:
+        yield
+    finally:
+        lease.host.release_managed_execution("test.request_client_reuse")
+        relay_runtime.SESSION_COORDINATOR.end_turn(turn, outcome="success")
+        relay_runtime.SESSION_COORDINATOR.release_conversation(lease)
+        relay_runtime._reset_for_tests()
+
+
 def _chunk(content=None, finish_reason=None):
     return SimpleNamespace(
         choices=[
@@ -154,6 +186,40 @@ def test_worker_interrupt_break_poisons_slot_when_stream_close_fails():
     assert "interrupt_stream_close_failed" in abort_reasons
 
 
+def test_relay_managed_close_failure_poisons_request_client(tmp_path, monkeypatch):
+    """Relay must preserve close failures needed by the reuse-slot guard."""
+    agent = _make_agent()
+
+    def chunks():
+        yield _chunk(content="partial ")
+        agent._interrupt_requested = True
+        yield _chunk(content="never processed")
+
+    stream = _FakeStream(chunks, close_raises=True)
+    request_client = _mock_wire_client(stream)
+    abort_reasons = []
+
+    with _managed_relay_turn(agent, tmp_path, monkeypatch), patch.object(
+        agent, "_create_request_openai_client", return_value=request_client
+    ), patch.object(agent, "_close_request_openai_client"), patch.object(
+        agent,
+        "_abort_request_openai_client",
+        side_effect=lambda client, *, reason: abort_reasons.append(
+            (client, reason)
+        ),
+    ):
+        with pytest.raises(InterruptedError):
+            agent._interruptible_streaming_api_call(
+                {
+                    "model": "test/model",
+                    "messages": [{"role": "user", "content": "hello"}],
+                }
+            )
+
+    assert stream.close_calls == 1
+    assert abort_reasons == [(request_client, "interrupt_stream_close_failed")]
+
+
 def test_stale_abort_is_atomic_with_holder_read(monkeypatch):
     """The stranger-thread abort must complete before the worker's finally
     can pop + cache the client.