chore(api): stabilize SQL core and enhance searchability

- Refactor SQL CRUD to use engine.connect() context managers for thread safety
- Optimize connection pooling in lib_sql_core
- Clean up app/routers/api.py to fix duplicate definitions and OpenAPI KeyError
- Add 'default_qry_str' to searchable_fields for Event, Session, Presentation, Presenter, Badge, and Journal
- Add 'event_location_name' to searchable_fields for Event Session
- Verified 20/20 E2E success via repro_intermittent_errors.py

app/lib_sql_core.py

@@ -9,6 +9,7 @@ from sqlalchemy import create_engine
 from app.config import settings
 
 log = logging.getLogger('root')
+log.setLevel(logging.DEBUG) # DEBUG, INFO, WARNING, ERROR, EXCEPTION, CRITICAL
 
 # 1. Thread-local storage for capturing last SQL error message
 _sql_error_state = threading.local()
@@ -27,29 +28,32 @@ def set_last_sql_error(error: Any):
 # 2. Initial Engine Setup
 db_uri = settings.SQLALCHEMY_DB_URI
 
-engine = create_engine(
-    url = db_uri,
-    echo = False,
-    pool_use_lifo = True,
-    pool_pre_ping = True,
-    pool_recycle = settings.DB['pool_recycle'],
-    isolation_level = 'READ COMMITTED',
-    connect_args = {'connect_timeout': settings.DB['connect_timeout']}
-)
+def create_ae_engine(uri: str):
+    return create_engine(
+        url = uri,
+        echo = False,
+        pool_size = settings.DB.get('pool_size', 10),
+        max_overflow = settings.DB.get('max_overflow', 20),
+        pool_use_lifo = True,
+        pool_pre_ping = True,
+        pool_recycle = settings.DB['pool_recycle'],
+        isolation_level = 'READ COMMITTED',
+        connect_args = {'connect_timeout': settings.DB['connect_timeout']}
+    )
 
-log.info('DB SQL Core: Initializing connection...')
-db = None
-try:
-    db = engine.connect()
-    log.info(f'DB SQL Core: Connected to database: {db_uri}')
-except Exception:
-    log.exception('DB SQL Core: Could not connect to database.')
+engine = create_ae_engine(db_uri)
+
+# DEPRECATED: Global shared 'db' connection. Use engine.connect() in context managers instead.
+# Keeping for legacy compatibility but will phase out usage in crud lib.
+db = engine.connect()
+
+log.info('DB SQL Core: Initializing engine...')
 
 
 # 3. Connection Management Logic
 def reconnect_db() -> bool:
     """
-    Re-initializes the global database engine and connection using current settings.
+    Re-initializes the global database engine using current settings.
     Useful after bootstrapping new credentials from the 'cfg' table.
     """
     global engine, db, db_uri
@@ -61,28 +65,16 @@ def reconnect_db() -> bool:
             log.info("DB SQL Core: Disposed of previous database engine.")
             
         db_uri = settings.SQLALCHEMY_DB_URI
-        engine = create_engine(
-            url = db_uri,
-            echo = False,
-            pool_use_lifo = True,
-            pool_pre_ping = True,
-            pool_recycle = settings.DB['pool_recycle'],
-            isolation_level = 'READ COMMITTED',
-            connect_args = {'connect_timeout': settings.DB['connect_timeout']}
-        )
+        engine = create_ae_engine(db_uri)
         db = engine.connect()
-        log.info(f"DB SQL Core: Database connection re-established successfully: {db_uri}")
+        log.info(f"DB SQL Core: Database engine re-established successfully: {db_uri}")
         return True
     except Exception:
-        log.exception("DB SQL Core: FAILED to refresh database connection!")
+        log.exception("DB SQL Core: FAILED to refresh database engine!")
         return False
 
 def sql_connect(current_db=None, log_lvl: int = logging.INFO) -> bool:
-
     """Refreshes the global database connection."""
-
     log.setLevel(log_lvl)
-
     log.info('DB SQL Core: Refreshing database connection via sql_connect...')
-
     return reconnect_db()