diff --git a/agent/agent_runtime_helpers.py b/agent/agent_runtime_helpers.py
index a418088916a95..bbaa688df7e02 100644
--- a/agent/agent_runtime_helpers.py
+++ b/agent/agent_runtime_helpers.py
@@ -1388,7 +1388,15 @@ def restore_primary_runtime(agent) -> bool:
         )
 
         # ── Rebuild client for the primary provider ──
-        if agent.api_mode == "anthropic_messages":
+        if agent.provider == "moa":
+            # MoA is a virtual chat-completions provider.  It never has real
+            # OpenAI client kwargs; restoring it after a fallback must recreate
+            # the facade, not call OpenAI() with an empty api_key.
+            from agent.moa_loop import MoAClient
+
+            agent.client = MoAClient(agent.model or "default")
+            agent._anthropic_client = None
+        elif agent.api_mode == "anthropic_messages":
             from agent.anthropic_adapter import build_anthropic_client
             agent._anthropic_api_key = rt["anthropic_api_key"]
             agent._anthropic_base_url = rt["anthropic_base_url"]
diff --git a/tests/run_agent/test_moa_loop_mode.py b/tests/run_agent/test_moa_loop_mode.py
index 50e3a0087244a..2a0b3df870993 100644
--- a/tests/run_agent/test_moa_loop_mode.py
+++ b/tests/run_agent/test_moa_loop_mode.py
@@ -81,6 +81,66 @@ def test_moa_runtime_provider_uses_virtual_endpoint():
     assert runtime["api_key"] == "moa-virtual-provider"
 
 
+def test_moa_primary_restore_rebuilds_virtual_facade(monkeypatch, tmp_path):
+    """MoA sessions must restore from fallback without constructing OpenAI().
+
+    Regression for a long-lived MoA session that failed over to a real provider:
+    the next turn restored provider/model to MoA but tried to rebuild the shared
+    client from MoA's empty client_kwargs, raising "api_key client option must be
+    set" and then "Failed to recreate closed OpenAI client".
+    """
+    home = tmp_path / ".hermes"
+    home.mkdir()
+    (home / "config.yaml").write_text(
+        """
+moa:
+  default_preset: review
+  presets:
+    review:
+      reference_models:
+        - provider: openai-codex
+          model: gpt-5.5
+      aggregator:
+        provider: openrouter
+        model: anthropic/claude-opus-4.8
+""".strip(),
+        encoding="utf-8",
+    )
+    monkeypatch.setenv("HERMES_HOME", str(home))
+
+    agent = AIAgent(
+        api_key="moa-virtual-provider",
+        base_url="moa://local",
+        model="review",
+        provider="moa",
+        quiet_mode=True,
+        skip_context_files=True,
+        skip_memory=True,
+        enabled_toolsets=["file"],
+        max_iterations=1,
+    )
+    primary_client = agent.client
+
+    def fail_openai_rebuild(*_args, **_kwargs):
+        raise AssertionError("MoA restore must not build a real OpenAI client")
+
+    monkeypatch.setattr(agent, "_create_openai_client", fail_openai_rebuild)
+    setattr(agent, "_fallback_activated", True)
+    setattr(agent, "provider", "zai")
+    setattr(agent, "model", "glm-5.2")
+    agent.base_url = "https://api.z.ai/api/coding/paas/v4"
+    agent.api_key = "fallback-key"
+    setattr(agent, "_client_kwargs", {"api_key": "fallback-key", "base_url": agent.base_url})
+    agent.client = SimpleNamespace(close=lambda: None, _client=SimpleNamespace(is_closed=True))
+
+    assert agent._restore_primary_runtime() is True
+    assert getattr(agent, "provider") == "moa"
+    assert getattr(agent, "model") == "review"
+    assert agent.client is not primary_client
+    assert hasattr(agent.client.chat, "completions")
+    assert getattr(agent, "_fallback_activated") is False
+
+
 def test_moa_does_not_cap_output_tokens(monkeypatch, tmp_path):
     """MoA must not inject an output cap on reference or aggregator calls.