fix(tests): join background scan/enrich workers before closing the DB (#735)

Root cause of the flaky pytest segfault (exit 139): the background scan and enrichment daemon threads (_scan_runner/_enrich_runner) use the shared MetadataDB connection, but test fixtures closed that connection in teardown without stopping them. A daemon thread mid-query on a freed SQLite conn is a native use-after-free → SIGSEGV. The app's startup kicks a scan, so almost any app-booting fixture was vulnerable. It only surfaced now because got-feedback/feedBack#728 added a push trigger, so ci/test runs on every push to main.

Fix: server.py retains the scan/enrich thread handles and adds _join_background_db_threads(); every test fixture now joins the workers before conn.close(). Verified: the full suite runs to completion (no segfault) where it previously crashed at ~25%.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_settings_api.py

@@ -75,6 +75,7 @@ def client(tmp_path, monkeypatch):
         meta_db = getattr(server, "meta_db", None)
         conn = getattr(meta_db, "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
 
 
@@ -296,6 +297,7 @@ def server_module(tmp_path, monkeypatch):
     meta_db = getattr(mod, "meta_db", None)
     conn = getattr(meta_db, "conn", None)
     if conn is not None:
+        getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
         conn.close()
 
 
@@ -324,6 +326,7 @@ def test_get_dlc_dir_uses_config_when_env_empty(tmp_path, monkeypatch):
     finally:
         conn = getattr(getattr(mod, "meta_db", None), "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
 
 
@@ -345,6 +348,7 @@ def test_get_dlc_dir_env_takes_precedence(tmp_path, monkeypatch):
     finally:
         conn = getattr(getattr(mod, "meta_db", None), "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
 
 
@@ -362,6 +366,7 @@ def test_get_dlc_dir_env_dot_is_valid(tmp_path, monkeypatch):
     finally:
         conn = getattr(getattr(mod, "meta_db", None), "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
 
 
@@ -404,6 +409,7 @@ def scan_module(tmp_path, monkeypatch, isolate_logging):
     yield mod
     conn = getattr(getattr(mod, "meta_db", None), "conn", None)
     if conn is not None:
+        getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
         conn.close()
 
 
@@ -525,6 +531,7 @@ def api_client(tmp_path, monkeypatch, isolate_logging):
     finally:
         conn = getattr(getattr(server, "meta_db", None), "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
         _restore_loaded_plugins(plugins_snapshot)
 
@@ -653,6 +660,7 @@ def test_skip_startup_tasks_does_not_call_load_plugins_or_scan(tmp_path, monkeyp
     finally:
         conn = getattr(getattr(server, "meta_db", None), "conn", None)
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
         _restore_loaded_plugins(plugins_snapshot)
 
@@ -698,6 +706,7 @@ def test_skip_startup_tasks_clears_stale_plugin_registry(tmp_path, monkeypatch,
     finally:
         conn = getattr(getattr(server, "meta_db", None), "conn", None) if server else None
         if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
             conn.close()
         _restore_loaded_plugins(plugins_snapshot)