diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 5735648f13..e812a337f5 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -916,6 +916,19 @@ def _try_openrouter() -> Tuple[Optional[OpenAI], Optional[str]]:
                    default_headers=_OR_HEADERS), _OPENROUTER_MODEL
 
 
+def _describe_openrouter_unavailable() -> str:
+    """Return a more precise OpenRouter auth failure reason for logs."""
+    pool_present, entry = _select_pool_entry("openrouter")
+    if pool_present:
+        if entry is None:
+            return "OpenRouter credential pool has no usable entries (credentials may be exhausted)"
+        if not _pool_runtime_api_key(entry):
+            return "OpenRouter credential pool entry is missing a runtime API key"
+    if not str(os.getenv("OPENROUTER_API_KEY") or "").strip():
+        return "OPENROUTER_API_KEY not set"
+    return "no usable OpenRouter credentials found"
+
+
 def _try_nous(vision: bool = False) -> Tuple[Optional[OpenAI], Optional[str]]:
     # Check cross-session rate limit guard before attempting Nous —
     # if another session already recorded a 429, skip Nous entirely
@@ -1627,8 +1640,10 @@ def resolve_provider_client(
     if provider == "openrouter":
         client, default = _try_openrouter()
         if client is None:
-            logger.warning("resolve_provider_client: openrouter requested "
-                           "but OPENROUTER_API_KEY not set")
+            logger.warning(
+                "resolve_provider_client: openrouter requested but %s",
+                _describe_openrouter_unavailable(),
+            )
             return None, None
         final_model = _normalize_resolved_model(model or default, provider)
         return (_to_async_client(client, final_model) if async_mode
diff --git a/tests/agent/test_auxiliary_client.py b/tests/agent/test_auxiliary_client.py
index 4c775b8a6c..b5b74bd309 100644
--- a/tests/agent/test_auxiliary_client.py
+++ b/tests/agent/test_auxiliary_client.py
@@ -447,6 +447,34 @@ class TestExplicitProviderRouting:
             adapter = client.chat.completions
             assert adapter._is_oauth is False
 
+    def test_explicit_openrouter_pool_exhausted_logs_precise_warning(self, monkeypatch, caplog):
+        monkeypatch.delenv("OPENROUTER_API_KEY", raising=False)
+        with patch("agent.auxiliary_client._select_pool_entry", return_value=(True, None)):
+            with caplog.at_level(logging.WARNING, logger="agent.auxiliary_client"):
+                client, model = resolve_provider_client("openrouter")
+        assert client is None
+        assert model is None
+        assert any(
+            "credential pool has no usable entries" in record.message
+            for record in caplog.records
+        )
+        assert not any(
+            "OPENROUTER_API_KEY not set" in record.message
+            for record in caplog.records
+        )
+
+    def test_explicit_openrouter_missing_env_keeps_not_set_warning(self, monkeypatch, caplog):
+        monkeypatch.delenv("OPENROUTER_API_KEY", raising=False)
+        with patch("agent.auxiliary_client._select_pool_entry", return_value=(False, None)):
+            with caplog.at_level(logging.WARNING, logger="agent.auxiliary_client"):
+                client, model = resolve_provider_client("openrouter")
+        assert client is None
+        assert model is None
+        assert any(
+            "OPENROUTER_API_KEY not set" in record.message
+            for record in caplog.records
+        )
+
 class TestGetTextAuxiliaryClient:
     """Test the full resolution chain for get_text_auxiliary_client."""