feat: persist isolated vector snapshots and exact retrieval

backend/app/core/config.py

@@ -1,7 +1,8 @@
 from pathlib import Path
+from typing import Literal
 from urllib.parse import urlsplit
 
-from pydantic import Field, model_validator
+from pydantic import Field, field_validator, model_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 
@@ -16,6 +17,11 @@ class Settings(BaseSettings):
     )
     auth_cookie_secure: bool = True
     auth_session_seconds: int = Field(28800, ge=300, le=604800)
+    embedding_enabled: bool = False
+    embedding_model: Literal["small", "base"] = "small"
+    embedding_cache_dir: Path | None = None
+    embedding_batch_size: int = Field(8, ge=1, le=32)
+    embedding_threads: int = Field(2, ge=1, le=4)
     model_config = SettingsConfigDict(
         env_file=Path(__file__).resolve().parents[2] / ".env", extra="ignore"
     )
@@ -28,6 +34,11 @@ class Settings(BaseSettings):
     def auth_origin_list(self) -> list[str]:
         return [x.strip() for x in self.auth_allowed_origins.split(",") if x.strip()]
 
+    @field_validator("embedding_cache_dir", mode="before")
+    @classmethod
+    def empty_embedding_cache_uses_default(cls, value):
+        return None if isinstance(value, str) and not value.strip() else value
+
     @model_validator(mode="after")
     def validate_auth_settings(self):
         if not self.auth_cookie_secure and self.app_env not in {"development", "test"}: