wip: implement websocket chat service with Pydantic models and session management

app/config.py

@@ -1,4 +1,5 @@
 import os
+from typing import Literal
 
 from pydantic import BaseModel, PostgresDsn, RedisDsn, computed_field
 from pydantic_core import MultiHostUrl
@@ -13,6 +14,25 @@ class SMTPConfig(BaseModel):
     template_path: str = os.getenv("EMAIL_TEMPLATE_PATH", "templates")
 
 
+class ChatConfig(BaseModel):
+    """Configuration for the websocket chat service's model-client adapter.
+
+    ``backend`` selects which :class:`~app.services.chat_agent.ChatAgent`
+    implementation is built by
+    :func:`~app.services.chat_agent.build_chat_agent` during app startup:
+
+    - ``"stub"``: a local, dependency-free echo agent (default, no network
+      calls, ideal for local dev/tests).
+    - ``"ollama"``: streams completions from an OpenAI-compatible endpoint
+      (e.g. a local Ollama server), reusing the same adapter interface.
+    """
+
+    backend: Literal["stub", "ollama"] = os.getenv("CHAT_BACKEND", "stub")
+    base_url: str = os.getenv("CHAT_BASE_URL", "http://localhost:11434/v1")
+    model: str = os.getenv("CHAT_MODEL", "llama3.2")
+    stream_delay_seconds: float = float(os.getenv("CHAT_STREAM_DELAY", "0.02"))
+
+
 class Settings(BaseSettings):
     model_config = SettingsConfigDict(
         env_file=".env", env_ignore_empty=True, extra="ignore"
@@ -21,6 +41,7 @@ class Settings(BaseSettings):
     jwt_expire: int = os.getenv("JWT_EXPIRE")
 
     smtp: SMTPConfig = SMTPConfig()
+    chat: ChatConfig = ChatConfig()
 
     REDIS_HOST: str
     REDIS_PORT: int