fix(arch): changement de role sans jeter la session, et en une transaction

ARCH-008. `role` est le discriminateur polymorphe, et SQLAlchemy fixe la
classe d une instance au chargement. edit_user ecrivait donc la colonne par
un UPDATE de niveau instruction puis relisait la ligne -- c est correct.
La suite ne l etait pas.

  db.session.commit()
  db.session.remove()   # discard stale session entirely
  user = User.query.get(user_id_local)

Deux defauts dans ces trois lignes.

1. remove() jette la session entiere. Tout ce que la requete tenait encore
   se retrouvait detache, current_user compris ; le moindre acces a un
   attribut ensuite levait DetachedInstanceError. La route ne survivait
   qu en ayant recopie le nom et l id de l acteur dans des variables
   locales avant -- un contournement, pas la correction. Un expunge de la
   seule instance perimee suffit.

2. Le commit intermediaire coupait l edition en deux. Le role etait acquis
   avant que le reste du formulaire soit applique : une erreur ensuite
   laissait un compte promu et le reste perdu, sans qu aucune interface ne
   le signale. Sans ce commit, l UPDATE reste dans la transaction, la
   relecture le voit, et l ensemble part en un seul commit.

Les evenements d audit passent apres le commit. account.role_changed etait
journalise avant l UPDATE : le journal affirmait un changement que la
transaction pouvait encore annuler.

tests/test_role_change.py, 6 tests. Un seul echoue sur le code d avant --
celui de l atomicite ; les cinq autres fixent le comportement qui marchait
deja, pour que la suite de la vague D ne le casse pas.

Co-Authored-By: Claude Opus 5 <[email protected]>

tests/test_role_change.py

@@ -0,0 +1,119 @@
+"""Changing a user's role — ARCH-008.
+
+`role` is the polymorphic discriminator, and SQLAlchemy fixes an instance's
+class at load time. edit_user therefore writes the column with a
+statement-level UPDATE and re-reads the row, which is correct. What it did
+next was not: it called db.session.remove(), throwing away the whole
+session, and it committed the role on its own before the rest of the edit
+had been applied.
+
+The two consequences these tests pin down:
+
+  - everything the request still held became detached, current_user
+    included. The route only survived because it had copied the actor's
+    name and id into locals beforehand — a workaround, in place of the fix.
+  - the role change was already committed when the rest of the edit ran, so
+    a failure afterwards left the account promoted and nothing else
+    applied.
+"""
+
+import pytest
+
+from app.extensions import db
+from app.models import Coach, Player, User
+
+
+def _edit(client, user_id, **overrides):
+    payload = {
+        'full_name': 'Promoted Person',
+        'email': '[email protected]',
+        'role': 'coach',
+        'is_active_account': 'on',
+    }
+    payload.update(overrides)
+    return client.post(f'/users/{user_id}/edit', data=payload, follow_redirects=True)
+
+
+class TestPolymorphicIdentity:
+    def test_the_account_takes_its_new_class(self, app, client, as_role, make_user):
+        target_id = make_user('player')
+        as_role('admin')
+
+        _edit(client, target_id)
+
+        with app.app_context():
+            assert isinstance(db.session.get(User, target_id), Coach)
+
+    def test_the_new_role_grants_its_pages_right_away(
+        self, app, client, as_role, make_user, login
+    ):
+        """isinstance() is how this application authorises; a stale class in
+        the identity map is a stale permission set."""
+        target_id = make_user('player')
+        as_role('admin')
+        _edit(client, target_id)
+
+        with app.app_context():
+            username = db.session.get(User, target_id).username
+        client.get('/auth/logout')
+        login(username)
+
+        # Coach-only, and it is a coach's own page rather than a redirect.
+        assert client.get('/users/notes-dashboard').status_code == 200
+
+    def test_the_other_fields_of_the_edit_land_too(
+        self, app, client, as_role, make_user
+    ):
+        target_id = make_user('player')
+        as_role('admin')
+
+        _edit(client, target_id, full_name='Renamed Too', phone='555-0100')
+
+        with app.app_context():
+            user = db.session.get(User, target_id)
+            assert user.full_name == 'Renamed Too'
+            assert user.phone == '555-0100'
+
+
+class TestTheActingPresident:
+    """db.session.remove() detached current_user mid-request."""
+
+    def test_the_president_keeps_their_session(self, client, as_role, make_user):
+        target_id = make_user('player')
+        as_role('admin')
+
+        _edit(client, target_id)
+
+        assert client.get('/users').status_code == 200
+
+    def test_the_response_renders(self, client, as_role, make_user):
+        target_id = make_user('player')
+        as_role('admin')
+
+        response = _edit(client, target_id)
+
+        assert response.status_code == 200
+
+
+class TestAtomicity:
+    def test_a_failure_after_the_update_leaves_the_role_alone(
+        self, app, client, as_role, make_user, monkeypatch
+    ):
+        """The role used to be committed on its own, before the rest of the
+        edit ran. A failure afterwards left an account promoted, and no
+        interface reported it."""
+        target_id = make_user('player')
+        as_role('admin')
+
+        def _explode(user, selected_games):
+            raise RuntimeError('storage unavailable')
+
+        monkeypatch.setattr('app.routes.users.update_user_gamertags', _explode)
+
+        with pytest.raises(RuntimeError):
+            _edit(client, target_id)
+
+        with app.app_context():
+            user = db.session.get(User, target_id)
+            assert isinstance(user, Player)
+            assert user.role == 'player'