diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 7192dfd5d..3ce0308ce 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -121,6 +121,11 @@ logger = logging.getLogger(__name__)
 # them independently.
 _LOGGED_UNKNOWN_PROVIDER_KEYS: set = set()
 _LOGGED_UNHANDLED_AUTHTYPE_KEYS: set = set()
+# Same treatment for the two "registered provider, unsupported sub-branch"
+# routing dead-ends — external-process and OAuth providers that fall through
+# with no matching handler. Keyed by provider name.
+_LOGGED_UNSUPPORTED_EXTPROC_KEYS: set = set()
+_LOGGED_UNSUPPORTED_OAUTH_KEYS: set = set()
 
 
 def _openai_http_client_kwargs(
@@ -4495,8 +4500,10 @@ def resolve_provider_client(
             logger.debug("resolve_provider_client: %s (%s)", provider, final_model)
             return (_to_async_client(client, final_model, is_vision=is_vision) if async_mode
                     else (client, final_model))
-        logger.warning("resolve_provider_client: external-process provider %s not "
-                       "directly supported", provider)
+        if provider not in _LOGGED_UNSUPPORTED_EXTPROC_KEYS:
+            _LOGGED_UNSUPPORTED_EXTPROC_KEYS.add(provider)
+            logger.debug("resolve_provider_client: external-process provider %s not "
+                         "directly supported", provider)
         return None, None
 
     elif pconfig.auth_type == "aws_sdk":
@@ -4541,8 +4548,10 @@ def resolve_provider_client(
         if provider == "xai-oauth":
             return resolve_provider_client("xai-oauth", model, async_mode)
         # Other OAuth providers not directly supported
-        logger.warning("resolve_provider_client: OAuth provider %s not "
-                       "directly supported, try 'auto'", provider)
+        if provider not in _LOGGED_UNSUPPORTED_OAUTH_KEYS:
+            _LOGGED_UNSUPPORTED_OAUTH_KEYS.add(provider)
+            logger.debug("resolve_provider_client: OAuth provider %s not "
+                         "directly supported, try 'auto'", provider)
         return None, None
 
     # Demoted from logger.warning to debug; dedup keyed on (auth_type,
diff --git a/tests/agent/test_auxiliary_client_resolve_dedup.py b/tests/agent/test_auxiliary_client_resolve_dedup.py
index 56f3115db..1bb7bbd94 100644
--- a/tests/agent/test_auxiliary_client_resolve_dedup.py
+++ b/tests/agent/test_auxiliary_client_resolve_dedup.py
@@ -50,3 +50,69 @@ class TestUnknownProviderDedup:
             if "unknown provider" in r.getMessage()
         ]
         assert len(recs) == 2
+
+
+class TestUnhandledAuthTypeDedup:
+    def setup_method(self):
+        ac._LOGGED_UNHANDLED_AUTHTYPE_KEYS.clear()
+
+    def test_unhandled_auth_type_logs_debug_once_not_warning(self, caplog, monkeypatch):
+        import hermes_cli.auth as auth
+        from hermes_cli.auth import ProviderConfig
+
+        # A registered provider whose auth_type matches no handled branch →
+        # the terminal "unhandled auth_type" fall-through.
+        bogus = ProviderConfig(
+            id="bogus_authtype",
+            name="Bogus",
+            auth_type="totally_unhandled_scheme",
+        )
+        patched = dict(auth.PROVIDER_REGISTRY)
+        patched["bogus_authtype"] = bogus
+        monkeypatch.setattr(auth, "PROVIDER_REGISTRY", patched)
+
+        with caplog.at_level(logging.DEBUG, logger="agent.auxiliary_client"):
+            client, model = resolve_provider_client("bogus_authtype", "")
+            resolve_provider_client("bogus_authtype", "")  # repeat → suppressed
+
+        assert (client, model) == (None, None)
+        recs = [
+            r for r in caplog.records
+            if "unhandled auth_type" in r.getMessage()
+        ]
+        # Two calls, one DEBUG record, never WARNING.
+        assert len(recs) == 1
+        assert recs[0].levelno == logging.DEBUG
+        assert not any(r.levelno >= logging.WARNING for r in recs)
+
+
+class TestUnsupportedOAuthDedup:
+    def setup_method(self):
+        ac._LOGGED_UNSUPPORTED_OAUTH_KEYS.clear()
+
+    def test_unsupported_oauth_provider_logs_debug_once(self, caplog, monkeypatch):
+        import hermes_cli.auth as auth
+        from hermes_cli.auth import ProviderConfig
+
+        # A registered oauth_* provider that is not one of the directly-handled
+        # names (nous / openai-codex / xai-oauth) → the OAuth dead-end branch.
+        bogus = ProviderConfig(
+            id="bogus_oauth",
+            name="BogusOAuth",
+            auth_type="oauth_device_code",
+        )
+        patched = dict(auth.PROVIDER_REGISTRY)
+        patched["bogus_oauth"] = bogus
+        monkeypatch.setattr(auth, "PROVIDER_REGISTRY", patched)
+
+        with caplog.at_level(logging.DEBUG, logger="agent.auxiliary_client"):
+            resolve_provider_client("bogus_oauth", "")
+            resolve_provider_client("bogus_oauth", "")
+
+        recs = [
+            r for r in caplog.records
+            if "OAuth provider" in r.getMessage() and "not " in r.getMessage()
+        ]
+        assert len(recs) == 1
+        assert recs[0].levelno == logging.DEBUG
+        assert not any(r.levelno >= logging.WARNING for r in recs)