runtime: route DeepSeek convention=anthropic to Anthropic client

src/plyngent/agent/messages_bridge.py

@@ -1,7 +1,9 @@
 """Convert agent chat history/tools to Anthropic Messages API shapes and back.
 
 Agent memory and events stay chat-completions-shaped; only the transport uses
-``POST /messages``. OpenAI / DeepSeek paths never enter this module.
+``POST /messages``. Real Anthropic and the DeepSeek ``convention="anthropic"``
+surface both route through this module; OpenAI / openai-compatible paths never
+enter it.
 """
 
 from __future__ import annotations

src/plyngent/agent/messages_dispatch.py

@@ -1,7 +1,9 @@
 """Anthropic Messages dispatch: present ``/messages`` as chat completions to the loop.
 
 Agent memory and events stay chat-completions-shaped; only the transport uses
-``POST /messages``. OpenAI / DeepSeek paths never enter this module.
+``POST /messages``. Real Anthropic and the DeepSeek ``convention="anthropic"``
+surface both route through this module; OpenAI / openai-compatible paths never
+enter it.
 """
 
 from __future__ import annotations

src/plyngent/runtime/client_factory.py

@@ -6,7 +6,11 @@ from typing import TYPE_CHECKING
 from plyngent.config.routing import EffectiveProvider, resolve_effective_provider
 from plyngent.lmproto.anthropic import AnthropicClient
 from plyngent.lmproto.anthropic.config import AnthropicConfig as AnthropicConfigCls
-from plyngent.lmproto.deepseek import DeepseekOpenAIClient, DeepseekResponsesClient
+from plyngent.lmproto.deepseek import (
+    DeepseekAnthropicClient,
+    DeepseekOpenAIClient,
+    DeepseekResponsesClient,
+)
 from plyngent.lmproto.openai import OpenAIClient
 from plyngent.lmproto.openai_compatible import OpenAICompatibleClient, OpenAIConfig
 from plyngent.lmproto.openai_compatible.config import (
@@ -23,7 +27,12 @@ DEFAULT_ANTHROPIC_BASE_URL = "https://api.anthropic.com/v1"
 DEFAULT_DEEPSEEK_BASE_URL = "https://api.deepseek.com"
 
 type ProtocolClient = (
-    OpenAIClient | OpenAICompatibleClient | DeepseekOpenAIClient | DeepseekResponsesClient | AnthropicClient
+    OpenAIClient
+    | OpenAICompatibleClient
+    | DeepseekOpenAIClient
+    | DeepseekResponsesClient
+    | DeepseekAnthropicClient
+    | AnthropicClient
 )
 # Backward-compatible name used by older imports/tests.
 type OpenAICompatibleClientUnion = ProtocolClient
@@ -94,13 +103,37 @@ def provider_to_openai_config(
     )
 
 
+def _anthropic_client(effective: EffectiveProvider) -> AnthropicClient:
+    """Build an Anthropic Messages client (real or DeepSeek convention) for *effective*."""
+    try:
+        http_timeout = normalize_http_timeout(effective.timeout)
+    except InvalidHttpTimeoutError as exc:
+        raise ProviderNotSupportedError(str(exc)) from exc
+    if effective.preset == "deepseek":
+        return DeepseekAnthropicClient(
+            AnthropicConfigCls(
+                api_key=effective.access_key_or_token,
+                base_url=effective.url or DEFAULT_DEEPSEEK_BASE_URL,
+                timeout=http_timeout,
+            )
+        )
+    return AnthropicClient(
+        AnthropicConfigCls(
+            api_key=effective.access_key_or_token,
+            base_url=effective.url or DEFAULT_ANTHROPIC_BASE_URL,
+            timeout=http_timeout,
+        )
+    )
+
+
 def create_client(provider: Provider, *, model: str | None = None) -> ProtocolClient:
     """Build a protocol client for *provider*, applying model-level routing.
 
     ``preset`` always decides API conventions: ``openai`` → /responses,
     ``openai-compatible`` → /chat/completions, ``anthropic`` → /messages.
-    Exception: a ``deepseek`` preset picks the Responses surface when its
-    effective ``convention`` is ``"responses"``, else chat completions.
+    Exception: a ``deepseek`` preset picks the Responses or Anthropic surface
+    when its effective ``convention`` is ``"responses"`` / ``"anthropic"``,
+    else chat completions.
     """
     effective = resolve_effective_provider(provider, model=model)
     if effective.preset == "openai":
@@ -110,18 +143,10 @@ def create_client(provider: Provider, *, model: str | None = None) -> ProtocolCl
     if effective.preset == "deepseek":
         if effective.convention == "responses":
             return DeepseekResponsesClient(provider_to_openai_config(effective))
+        if effective.convention == "anthropic":
+            return _anthropic_client(effective)
         return DeepseekOpenAIClient(provider_to_openai_config(effective))
     if effective.preset == "anthropic":
-        try:
-            http_timeout = normalize_http_timeout(effective.timeout)
-        except InvalidHttpTimeoutError as exc:
-            raise ProviderNotSupportedError(str(exc)) from exc
-        return AnthropicClient(
-            AnthropicConfigCls(
-                api_key=effective.access_key_or_token,
-                base_url=effective.url or DEFAULT_ANTHROPIC_BASE_URL,
-                timeout=http_timeout,
-            )
-        )
+        return _anthropic_client(effective)
     msg = f"provider preset {effective.preset!r} is not supported"
     raise ProviderNotSupportedError(msg)

tests/test_runtime/test_client_factory.py

@@ -89,8 +89,54 @@ def test_deepseek_default_and_legacy_conventions_stay_chat() -> None:
     default_client = create_client(DeepseekProvider(access_key_or_token="sk-test"))
     assert isinstance(default_client, DeepseekOpenAIClient)
     assert not isinstance(default_client, DeepseekResponsesClient)
-    legacy = DeepseekProvider(access_key_or_token="sk-test", convention="anthropic")
-    assert isinstance(create_client(legacy), DeepseekOpenAIClient)
+    # extras.convention stays ignored (legacy location).
+    legacy_extra = DeepseekProvider(
+        access_key_or_token="sk-test",
+        extras={"convention": "anthropic"},
+    )
+    assert isinstance(create_client(legacy_extra), DeepseekOpenAIClient)
+
+
+def test_deepseek_anthropic_convention() -> None:
+    from plyngent.lmproto.anthropic import AnthropicClient
+    from plyngent.lmproto.deepseek import DeepseekAnthropicClient
+
+    provider = DeepseekProvider(access_key_or_token="sk-test", convention="anthropic")
+    client = create_client(provider)
+    assert isinstance(client, DeepseekAnthropicClient)
+    assert isinstance(client, AnthropicClient)
+    assert client.kind == "messages"
+    assert client.session.base_url == "https://api.deepseek.com/anthropic"
+
+
+def test_deepseek_anthropic_convention_custom_url() -> None:
+    from plyngent.lmproto.deepseek import DeepseekAnthropicClient
+
+    provider = DeepseekProvider(
+        access_key_or_token="sk-test",
+        url="https://gateway.example/anthropic",
+        convention="anthropic",
+    )
+    client = create_client(provider)
+    assert isinstance(client, DeepseekAnthropicClient)
+    assert client.session.base_url == "https://gateway.example/anthropic"
+
+
+def test_deepseek_model_level_anthropic_convention() -> None:
+    from plyngent.lmproto.deepseek import DeepseekAnthropicClient, DeepseekOpenAIClient
+
+    provider = DeepseekProvider(
+        access_key_or_token="sk-test",
+        models={
+            "claude-proxy": ModelConfig(convention="anthropic"),
+            "deepseek-v4-flash": ModelConfig(),
+        },
+    )
+    proxy = create_client(provider, model="claude-proxy")
+    assert isinstance(proxy, DeepseekAnthropicClient)
+    assert proxy.session.base_url == "https://api.deepseek.com/anthropic"
+    flash = create_client(provider, model="deepseek-v4-flash")
+    assert isinstance(flash, DeepseekOpenAIClient)
 
 
 def test_deepseek_model_level_convention_override() -> None: