feat(tests): scaffold + integration smoke tests (config, db, models, pipeline)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/scaffold/test_config.py

@@ -0,0 +1,35 @@
+"""Smoke tests for codex.config.Settings."""
+
+from __future__ import annotations
+
+from codex.config import Settings, get_settings
+
+
+def test_settings_defaults() -> None:
+    """Settings() is constructable without env vars; expected defaults are set."""
+    s = Settings()
+    assert s.database_url == "postgresql://researcher:change_me@localhost:5432/papers"
+    assert s.embedding_model == "BAAI/bge-m3"
+    assert s.embedding_dim == 1024
+
+
+def test_settings_env_override(monkeypatch: object) -> None:
+    """DATABASE_URL env var overrides the default database_url."""
+    import pytest
+
+    mp: pytest.MonkeyPatch = monkeypatch  # type: ignore[assignment]
+    mp.setenv("DATABASE_URL", "postgresql://x:y@h:5432/db")
+    s = Settings()
+    assert s.database_url == "postgresql://x:y@h:5432/db"
+
+
+def test_get_settings_is_singleton() -> None:
+    """get_settings() returns the same object on repeated calls; new object after cache_clear."""
+    get_settings.cache_clear()
+    first = get_settings()
+    second = get_settings()
+    assert first is second
+
+    get_settings.cache_clear()
+    third = get_settings()
+    assert third is not first