feat: Implement environment variable fallback for configuration settings

backend/config/__init__.py

@@ -15,6 +15,15 @@ def _parse_csv_env(name: str) -> tuple[str, ...]:
     return tuple(item.strip().lower() for item in raw_value.split(",") if item.strip())
 
 
+def _env_or_default(name: str, default: str) -> str:
+    raw_value = os.getenv(name)
+    if raw_value is None:
+        return default
+
+    normalized = raw_value.strip()
+    return normalized or default
+
+
 class BaseConfig:
     """Base configuration."""
     SECRET_KEY = os.getenv("SECRET_KEY", "change-me-in-production")
@@ -25,10 +34,10 @@ class BaseConfig:
     MAX_CONTENT_LENGTH = int(
         os.getenv("ABSOLUTE_MAX_CONTENT_LENGTH_MB", 100)
     ) * 1024 * 1024
-    UPLOAD_FOLDER = os.getenv("UPLOAD_FOLDER", "/tmp/uploads")
-    OUTPUT_FOLDER = os.getenv("OUTPUT_FOLDER", "/tmp/outputs")
+    UPLOAD_FOLDER = _env_or_default("UPLOAD_FOLDER", "/tmp/uploads")
+    OUTPUT_FOLDER = _env_or_default("OUTPUT_FOLDER", "/tmp/outputs")
     FILE_EXPIRY_SECONDS = int(os.getenv("FILE_EXPIRY_SECONDS", 1800))
-    DATABASE_PATH = os.getenv(
+    DATABASE_PATH = _env_or_default(
         "DATABASE_PATH", os.path.join(BASE_DIR, "data", "dociva.db")
     )
     PERMANENT_SESSION_LIFETIME = timedelta(days=30)

backend/tests/test_config.py

@@ -1,4 +1,7 @@
 """Tests for GET /api/config — dynamic upload limits."""
+import importlib
+import os
+
 import pytest
 
 
@@ -51,3 +54,22 @@ class TestConfigEndpoint:
         data = resp.get_json()
         limits = data["file_limits_mb"]
         assert data["max_upload_mb"] == max(limits.values())
+
+
+class TestConfigEnvironmentFallbacks:
+    """Tests for environment values that should not accept blank strings."""
+
+    def test_blank_database_path_falls_back_to_default(self, monkeypatch):
+        """A blank DATABASE_PATH must not create a temporary per-connection SQLite DB."""
+        monkeypatch.setenv("DATABASE_PATH", "")
+
+        import config as config_module
+
+        reloaded = importlib.reload(config_module)
+        try:
+            expected = os.path.join(reloaded.BASE_DIR, "data", "dociva.db")
+            assert reloaded.BaseConfig.DATABASE_PATH == expected
+            assert reloaded.ProductionConfig.DATABASE_PATH == expected
+        finally:
+            monkeypatch.delenv("DATABASE_PATH", raising=False)
+            importlib.reload(config_module)