fix(tests): isolate database and module state

tests/conftest.py

@@ -8,15 +8,12 @@ import pytest
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
-# Importing core.database below runs init_db() at import time, and its default
-# (sqlite:///./data/app.db) can't be opened in a clean worktree because SQLite
-# won't create the missing ./data parent dir - pytest then dies during
-# collection, before any test module loads. Default to an in-memory DB for the
-# test session so collection is deterministic and writes no repo-local
-# artifacts. An explicit DATABASE_URL (a real test/CI database) is preserved.
-# This only unblocks collection/import-time init; it does not provide a shared
-# file-backed DB across processes - tests needing that must set DATABASE_URL.
-os.environ.setdefault("DATABASE_URL", "sqlite:///:memory:")
+# core.database initializes its engine during import. Always isolate that
+# bootstrap from an inherited developer DATABASE_URL, before collection can
+# import it. Tests needing files own their disposable databases explicitly.
+# Restore the caller's environment when pytest's configuration is torn down.
+_database_environment = pytest.MonkeyPatch()
+_database_environment.setenv("DATABASE_URL", "sqlite:///:memory:")
 
 # Pre-import real heavy modules BEFORE any test file's module-level stubs can
 # replace them with MagicMock. Some test files (e.g. test_llm_core_sanitize_*)
@@ -101,6 +98,8 @@ def pytest_configure(config):
     unknown-mark warnings still surface genuine typos outside the taxonomy. This
     only registers marker names; it imports no production module.
     """
+    config.add_cleanup(_database_environment.undo)
+
     import pathlib
     from tests._taxonomy import discover_markers