diff --git a/agent/credential_pool.py b/agent/credential_pool.py
index 28f9089489..6b36bf4554 100644
--- a/agent/credential_pool.py
+++ b/agent/credential_pool.py
@@ -1416,6 +1416,11 @@ class CredentialPool:
         entries_to_prune: List[str] = []
         available: List[PooledCredential] = []
         for entry in self._entries:
+            # Borrowed credentials persist as metadata-only references and are
+            # hydrated from their live source on load.  A stale duplicate row
+            # can remain unhydrated; never lease or select it as an empty key.
+            if entry.auth_type == AUTH_TYPE_API_KEY and not entry.runtime_api_key:
+                continue
             # For anthropic claude_code entries, sync from the credentials file
             # before any status/refresh checks. This picks up tokens refreshed
             # by other processes (Claude Code CLI, other Hermes profiles).
@@ -1732,11 +1737,15 @@ class CredentialPool:
 
 
 def _upsert_entry(entries: List[PooledCredential], provider: str, source: str, payload: Dict[str, Any]) -> bool:
-    existing_idx = None
+    matching_indices = []
     for idx, entry in enumerate(entries):
         if entry.source == source:
-            existing_idx = idx
-            break
+            matching_indices.append(idx)
+
+    existing_idx = matching_indices[0] if matching_indices else None
+    duplicate_indices = set(matching_indices[1:])
+    if duplicate_indices:
+        entries[:] = [entry for idx, entry in enumerate(entries) if idx not in duplicate_indices]
 
     if existing_idx is None:
         payload.setdefault("id", uuid.uuid4().hex[:6])
@@ -1768,8 +1777,8 @@ def _upsert_entry(entries: List[PooledCredential], provider: str, source: str, p
         # Runtime-only borrowed secret updates should refresh the in-memory
         # entry without forcing auth.json churn when the disk-safe payload is
         # unchanged (for example env keys with the same fingerprint).
-        return existing.to_dict() != updated.to_dict()
-    return False
+        return bool(duplicate_indices) or existing.to_dict() != updated.to_dict()
+    return bool(duplicate_indices)
 
 
 def _normalize_pool_priorities(provider: str, entries: List[PooledCredential]) -> bool:
diff --git a/tests/agent/test_credential_pool.py b/tests/agent/test_credential_pool.py
index ae28580d85..68a923355e 100644
--- a/tests/agent/test_credential_pool.py
+++ b/tests/agent/test_credential_pool.py
@@ -831,6 +831,70 @@ def test_load_pool_does_not_persist_env_seeded_secret_value(tmp_path, monkeypatc
     assert persisted["secret_fingerprint"].startswith("sha256:")
 
 
+def test_load_pool_collapses_duplicate_env_rows_to_active_key(tmp_path, monkeypatch):
+    """One env source is one credential, even if auth.json contains stale duplicates."""
+    key = "sk-or-active-main-key"
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "hermes"))
+    monkeypatch.setenv("OPENROUTER_API_KEY", key)
+    _write_auth_store(
+        tmp_path,
+        {
+            "version": 1,
+            "credential_pool": {
+                "openrouter": [
+                    {
+                        "id": "current-row",
+                        "label": "OPENROUTER_API_KEY",
+                        "auth_type": "api_key",
+                        "priority": 0,
+                        "source": "env:OPENROUTER_API_KEY",
+                    },
+                    {
+                        "id": "stale-duplicate",
+                        "label": "OPENROUTER_API_KEY",
+                        "auth_type": "api_key",
+                        "priority": 1,
+                        "source": "env:OPENROUTER_API_KEY",
+                    },
+                ]
+            },
+        },
+    )
+
+    from agent.credential_pool import load_pool
+
+    pool = load_pool("openrouter")
+
+    assert [(entry.id, entry.runtime_api_key) for entry in pool.entries()] == [
+        ("current-row", key)
+    ]
+    persisted = json.loads((tmp_path / "hermes" / "auth.json").read_text())
+    assert [entry["id"] for entry in persisted["credential_pool"]["openrouter"]] == [
+        "current-row"
+    ]
+
+
+def test_credential_pool_never_selects_empty_borrowed_entry():
+    from agent.credential_pool import CredentialPool, PooledCredential
+
+    pool = CredentialPool(
+        "openrouter",
+        [
+            PooledCredential(
+                provider="openrouter",
+                id="metadata-only",
+                label="OPENROUTER_API_KEY",
+                auth_type="api_key",
+                priority=0,
+                source="env:OPENROUTER_API_KEY",
+                access_token="",
+            )
+        ],
+    )
+
+    assert pool.select() is None
+    assert pool.acquire_lease() is None
+
 
 def test_load_pool_persists_bitwarden_origin_metadata_without_secret(tmp_path, monkeypatch):
     """Bitwarden-injected env vars retain source metadata but not raw values."""