flask error with SQLAlchemy / ORM -- not seeing db tables

In development (so sqlite3) I'm getting this error on any database access:

sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: ujs ...

I got here by saying

export FLASK_ENV=development
export FLASK_APP=my_app.py
flask db init
flask db migrate
flask db upgrade
flask run

and then doing an HTTP GET against that dev server.

I believe the migration workflow succeeded, because when I use the sqlite3 commandline client, I can see the (empty) table with a believably correct schema.

╭╴ (get-db-working *%=)╶╮
╰ jeff@starshine:TN_flask_web $ sqlite3 dev.db 
SQLite version 3.27.2 2019-02-25 16:06:06
Enter ".help" for usage hints.
sqlite> .table
alembic_version    ujs
sqlite> .quit
╭╴ (get-db-working *%=)╶╮
╰ jeff@starshine:TN_flask_web $ 

I therefore believe I've made a coding error. But I'm not seeing it.

I have this code (pared down to what I believe is the essential bits):

my_app.py:

from app import create_app, db, cli
from app.models import UJS

app = create_app()
cli.register(app)

@app.shell_context_processor
def make_shell_context():
    return {'db': db,
            'UJS': UJS}

app/models.py:

from app import db
import time

def now_in_microseconds():
    """Return the current time in microseconds since the epoch.
    """
    return time.time() * 1000 * 1000

class UJS(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    timestamp_microseconds = db.Column(db.BigInteger, default=now_in_microseconds)
    ip_hash = db.column(db.String(40))

    # And then some more columns, all quite boring.

    def __repr__(self):
        return '<[{tag}]/[{ip}] {microsec}/{city}>'.format(
            tag=self.tag, ip=self.ip_hash,
            microsec=self.timestamp_microseconds, city=self.city)

app/__init__.py:

from flask import Flask, request, current_app
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from config import Config

db = SQLAlchemy()
migrate = Migrate()

def create_app(config_class=Config):
    app = Flask(__name__)
    app.config.from_object(config_class)
    try:
        app.config.from_pyfile("../config_local.py")
    except FileNotFoundError:
        print('No local config found.')
    except:
        print('Unexpected error on app.config.from_pyfile()')

    db.init_app(app)
    migrate.init_app(app, db)
    ...
    return app

from app import models

and app/main/routes.py:

from flask import request, g, current_app, session
from app import db
from app.main import bp
from app.models import UJS

@bp.before_app_request
def before_request():
    if 'static' == request.endpoint:
        # This should only happen in dev.  Otherwise, nginx handles static routes directly.
        return
    # I expect this to return an empty list, but it throws a 500.
    print(UJS.query.all())

Any suggestions what I'm missing?