autogenerate with SQLite foreign key and the uuid naming constraint recipe doesn't get DROP name

I was posting on stackoverflow my question: https://stackoverflow.com/questions/62787923/alembic-migration-doesnt-generate-uuid-correctly

I sat up my calling conventions like this:

def fk_guid(constraint, table):
    str_tokens = [
        table.name,
    ] + [
        element.parent.name for element in constraint.elements
    ] + [
        element.target_fullname for element in constraint.elements
    ]

    guid = uuid.uuid5(uuid.NAMESPACE_OID, "_".join(str_tokens))
    return str(guid)

convention = {
  "fk_guid": fk_guid,
  "ix": "ix_%(column_0_label)s",
  "uq": "uq_%(table_name)s_%(column_0_name)s",
  "ck": "ck_%(table_name)s_%(column_0_name)s",
  "fk": "fk_%(fk_guid)s",
#  "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
  "pk": "pk_%(table_name)s",
}

and two simple tables:

class TableA(Base):
    __tablename__ = 'table_a'

    id = Column(Integer, primary_key=True)
    name = Column(String(30), nullable=False, unique=True)
    table_b = Column(Integer, ForeignKey('table_b.id'), nullable=False)


class TableB(Base):
    __tablename__ = 'table_b'

    id = Column(Integer, primary_key=True)
    name = Column(String(30), nullable=False, unique=True)

The creation code of the constraint looks good:

sa.ForeignKeyConstraint(['table_b'], ['table_b.id'], name=op.f('fk_9d68bd30-b17a-565a-aee7-7bd21e90672e')),

And when I call alembic upgrade head:

str_tokens: ['table_a', 'table_b', 'table_b.id']

But the drop constraint code doesnt:

batch_op.drop_constraint(None, type_='foreignkey')

And when I call alembic upgrade head, it fails miserably trying to pass table_a but no constraints into the fk_guid function:

string_tokens: ['table_a']
...
KeyError: 'fk_94a3a57e-9747-5b39-8489-c1d273ca1bc2'

When I don't use user defined tokens (fk_guid), it works fine, but due to long constraint names, mariadb doesn't work anymore. (we're using sqlite3 for dev and mariadb as dev, test and production db)

Start by reproducing the SQLite case with the shown naming convention and compare the generated create and drop operations, especially batch_op.drop_constraint(None, type_='foreignkey'). Trace the autogenerate and batch operation path until the user-defined fk_guid receives the needed constraint context; done means the generated DROP has a usable name and alembic upgrade head succeeds.