feat: add embedding types, port and openai-compat transport

src/polygateway/ports.py

@@ -10,7 +10,14 @@ from dataclasses import dataclass
 from enum import StrEnum
 from typing import Any, Protocol, runtime_checkable
 
-from .types import ChatRequest, LLMResponse, SourceConfig, SourceStats, TransportResult
+from .types import (
+    ChatRequest,
+    EmbeddingTransportResult,
+    LLMResponse,
+    SourceConfig,
+    SourceStats,
+    TransportResult,
+)
 
 CallNext = Callable[[ChatRequest], Awaitable[LLMResponse]]
 
@@ -37,6 +44,15 @@ class Transport(Protocol):
     ) -> TransportResult: ...
 
 
+@runtime_checkable
+class EmbeddingTransport(Protocol):
+    """一次原始 embedding 调用的协议细节(M2 §7);不含任何治理。"""
+
+    async def embed(
+        self, *, texts: list[str], source: SourceConfig, call_id: str
+    ) -> EmbeddingTransportResult: ...
+
+
 @runtime_checkable
 class Permit(Protocol):
     """限流入场许可;settle/release 均幂等,finally 中必然执行。"""