experiment: test model_class= fix for FSA 3.x break (DO NOT MERGE)

Investigation-only commit for discussion #40273 / PR #42542's revert.
Passes model_class=flask_appbuilder.models.sqla.Model explicitly when
constructing SQLA() in superset/extensions/__init__.py, testing the
theory that FAB's FSA-3.x shim (base.py) leaves Superset's models and
db.session looking at two disconnected declarative registries, since
unlike the FSA-2.x shim (base_legacy.py) it never wires model_class
through.

Local pytest runs against sqlite reproduce neither the break nor a fix
signal (matches PR #42542's original finding that this only surfaced
under real CI). This commit exists to get a real CI signal on
test-sqlite/test-mysql before deciding whether to pursue this as an
actual fix (and whether it needs an upstream flask-appbuilder change
too, or is fixable entirely on Superset's side as this attempts).

pyproject.toml

@@ -60,15 +60,11 @@ dependencies = [
     "flask-login>=0.6.0, < 1.0",
     "flask-migrate>=4.1.0, <5.0",
     "flask-session>=0.4.0, <1.0",
-    # Pinned explicitly below 3.0: 3.0.5 resolves without conflict and
-    # supports both SQLAlchemy 1.4 and 2.0, but real CI runs surfaced a
-    # structural incompatibility with Superset's current session/app-context
-    # handling across Celery task boundaries (see PR #42542) -- widespread
-    # "NoneType has no attribute X" failures and MySQL lock-wait timeouts,
-    # not just a connection-pool quirk. Needs dedicated investigation, not a
-    # driver-compat-prep bump; revisit alongside the actual SQLAlchemy 2.0
-    # core bump (discussion #40273, step 6).
-    "flask-sqlalchemy>=2.5.1, <3.0",
+    # EXPERIMENTAL: testing whether passing model_class= explicitly when
+    # constructing SQLA() (see superset/extensions/__init__.py) resolves the
+    # PR #42542 regression before committing to a real bump. Do not merge
+    # this pin change as-is.
+    "flask-sqlalchemy>=3.0.5, <3.1",
     "flask-wtf>=1.3.0, <2.0",
     "geopy",
     "greenlet<=3.5.4, >=3.5.4",

requirements/base.txt

@@ -148,7 +148,7 @@ flask-migrate==4.1.0
     # via apache-superset (pyproject.toml)
 flask-session==0.8.0
     # via apache-superset (pyproject.toml)
-flask-sqlalchemy==2.5.1
+flask-sqlalchemy==3.0.5
     # via
     #   apache-superset (pyproject.toml)
     #   flask-appbuilder

requirements/development.txt

@@ -309,7 +309,7 @@ flask-session==0.8.0
     # via
     #   -c requirements/base-constraint.txt
     #   apache-superset
-flask-sqlalchemy==2.5.1
+flask-sqlalchemy==3.0.5
     # via
     #   -c requirements/base-constraint.txt
     #   apache-superset

superset/extensions/__init__.py

@@ -154,7 +154,9 @@ async_query_manager: AsyncQueryManager = LocalProxy(
 cache_manager = CacheManager()
 celery_app = celery.Celery()
 csrf = CSRFProtect()
-db = get_sqla_class()()
+from flask_appbuilder.models.sqla import Model as _FABModel  # noqa: E402
+
+db = get_sqla_class()(model_class=_FABModel)
 
 # make_versioned() MUST be called immediately after db is constructed and before
 # any versioned model class is defined.  Continuum patches the SQLAlchemy