fix(routing): union configured and known providers

src/rotator_library/routing_policy.py

@@ -45,7 +45,9 @@ def __init__(
 
         self.model_overrides = model_overrides
         self.available_providers = set(available_providers)
-        self.known_providers = set(known_providers or self.available_providers)
+        # A provider is valid for config validation if it has credentials,
+        # a loaded plugin, or both.
+        self.known_providers = self.available_providers | set(known_providers or ())
         self.provider_models = provider_models or {}
         self.rng = rng or random.Random()
         self._validate()

tests/test_routing_policy.py

@@ -119,6 +119,16 @@ def test_provider_model_mismatch_fails_validation_when_models_are_known():
         )
 
 
+def test_provider_in_available_providers_remains_known_when_plugins_differ():
+    policy = RoutingPolicy(
+        model_overrides={},
+        available_providers={"ollama", "chutes"},
+        known_providers={"opencode_go"},
+    )
+
+    assert policy.known_providers == {"ollama", "chutes", "opencode_go"}
+
+
 def test_weighted_override_rewrites_qwen3_5_to_allowed_provider():
     policy = RoutingPolicy(
         model_overrides={