core/config: default DeepSeek models v4-flash and v4-pro

When preset deepseek omits models, seed deepseek-v4-flash and
deepseek-v4-pro as text-capable entries for selection and docs.

tests/test_config/test_config.py

@@ -43,6 +43,9 @@ def test_read_valid_config() -> None:
     assert isinstance(providers["test2"], OpenAICompatibleProvider)
     assert isinstance(providers["test3"], AnthropicProvider)
     assert isinstance(providers["foo1"], DeepseekProvider)
+    # TOML omitted models → DeepSeek defaults.
+    assert set(providers["foo1"].models) == {"deepseek-v4-flash", "deepseek-v4-pro"}
+    assert providers["foo1"].models["deepseek-v4-flash"].text is True
     db = config.database
     assert db["implementation"] == "sqlite"
     assert db["url"] == ":memory:"
@@ -50,6 +53,21 @@ def test_read_valid_config() -> None:
     assert db["password"] is None
 
 
+def test_deepseek_default_models_on_construct() -> None:
+    provider = DeepseekProvider(access_key_or_token="sk-test")
+    assert set(provider.models) == {"deepseek-v4-flash", "deepseek-v4-pro"}
+
+
+def test_deepseek_explicit_models_override_defaults() -> None:
+    from plyngent.config import ModelConfig
+
+    provider = DeepseekProvider(
+        access_key_or_token="sk-test",
+        models={"custom-only": ModelConfig(text=True)},
+    )
+    assert set(provider.models) == {"custom-only"}
+
+
 def test_read_empty_config() -> None:
     config = plyngent.config.load(Path(__file__).parent / "plyngent-empty.toml")
     assert isinstance(config.providers, Mapping)

tests/test_runtime/test_client_factory.py

@@ -43,6 +43,8 @@ def test_deepseek_openai_convention() -> None:
     client = create_client(provider)
     assert isinstance(client, DeepseekOpenAIClient)
     assert provider_to_openai_config(provider).base_url == "https://api.deepseek.com/v1"
+    assert "deepseek-v4-flash" in provider.models
+    assert "deepseek-v4-pro" in provider.models
 
 
 def test_deepseek_anthropic_convention_not_implemented() -> None: