1. **Scaffold a FastAPI project in ./shortener**: Create the directory, initialize a virtual environment, and install dependencies. 2. **Add a /shorten POST endpoint and a /{code} GET redirect**: Write the main application file (`main.py`) with the required endpoints. 3. **Persist mappings in a SQLite DB**: Write the database setup and interaction code (can be integrated into `main.py` or a separate `db.py` file). Let's keep it simple and put it in `main.py` or a separate `db.py` for cleanliness. I'll use a separate `db.py` file. 4. **Run tests with pytest**: Write a `test_main.py` file and run the tests. 5. **Build and run a Docker image locally**: Write a `Dockerfile`, build the image, and run the container. 6. **Verify with an http_request**: Use the `http_request` tool to test the endpoints. Let's refine the steps to be specific and under 20 steps. Step 1: Create the project directory and navigate into it. Step 2: Create a virtual environment and install dependencies (fastapi, uvicorn, aiosqlite, pytest, httpx). Step 3: Write the database module (`db.py`) to handle SQLite connections and CRUD operations. Step 4: Write the FastAPI application (`main.py`) with the `/shorten` POST and `/{code}` GET endpoints, importing the DB module. Step 5: Write the test file (`test_main.py`) to test the endpoints using `httpx.AsyncClient`. Step 6: Run the tests using `pytest`. Step 7: Write the `Dockerfile` to containerize the application. Step 8: Build the Docker image. Step 9: Run the Docker container locally. Step 10: Verify the `/shorten` endpoint using `http_request`. Step 11: Verify the `/{code}` redirect endpoint using `http_request`. Let's double-check the constraints: - Numbered plan of shell and tool calls. - Specific about actual commands and file paths. - Do not write full app code. - Keep it to 20 steps or fewer. Step 1: `shell(cmd="mkdir -p shortener && cd shortener")` Step 2: `shell(cmd="python -m venv venv && source venv/bin/activate && pip install fastapi uvicorn aiosqlite pytest httpx")` Step 3: `write_file(path="shortener/db.py", contents="...")` (I will describe the contents briefly or just say write the file with the DB logic). Step 4: `write_file(path="shortener/main.py", contents="...")` (Write the app logic). Step 5: `write_file(path="shortener/test_main.py", contents="...")` (Write the tests). Step 6: `shell(cmd="cd shortener && python -m pytest test_main.py")` Step 7: `write_file(path="shortener/Dockerfile", contents="...")` (Write the Dockerfile). Step 8: `shell(cmd="cd shortener && docker build -t shortener-app .")` Step 9: `shell(cmd="docker run -p 8000:8000 shortener-app")` Step 10: `http_request(method="POST", url="http://localhost:8000/shorten", body='{"url": "https://example.com"}')` Step 11: `http_request(method="GET", url="http://localhost:8000/")` (where `` is the response from step 10). Wait, I need to make sure the `write_file` contents are described or just written out? The prompt says "Do not write the full app code - only the steps and key command strings." So I will just describe what goes into the files or write a minimal representation. Let's refine Step 3, 4, 5, 7 to be more specific about the key command strings / file contents without writing the full app. Step 3: `write_file(path="shortener/db.py", contents="import aiosqlite\n\nasync def init_db():\n conn = await aiosqlite.connect('shortener.db')\n await conn.execute('CREATE TABLE IF NOT EXISTS mappings (code TEXT PRIMARY KEY, url TEXT)')\n await conn.commit()\n return conn\n\nasync def add_mapping(code, url):\n conn = await init_db()\n await conn.execute('INSERT INTO mappings VALUES (?, ?)', (code, url))\n await conn.commit()\n await conn.close()\n\nasync def get_url(code):\n conn = await init_db()\n cursor = await conn.execute('SELECT url FROM mappings WHERE code = ?', (code,))\n row = await cursor.fetchone()\n await conn.close()\n return row[0] if row else None")` -> This is a bit long. I'll summarize the contents. Actually, the prompt says "Do not write the full app code - only the steps and key command strings." So I will write a summary of the file contents. Let's structure the response clearly. 1. `shell(cmd="mkdir -p shortener && cd shortener")` 2. `shell(cmd="python -m venv venv && source venv/bin/activate && pip install fastapi uvicorn aiosqlite pytest httpx")` 3. `write_file(path="shortener/db.py", contents="...")` 4. `write_file(path="shortener/main.py", contents="...")` 5. `write_file(path="shortener/test_main.py", contents="...")` 6. `shell(cmd="cd shortener && python -m pytest test_main.py")` 7. `write_file(path="shortener/Dockerfile", contents="...")` 8. `shell(cmd="cd shortener && docker build -t shortener-app .")` 9. `shell(cmd="docker run -p 8000:8000 shortener-app")` 10. `http_request(method="POST", url="http://localhost:8000/shorten", body='{"url": "https://example.com"}')` 11. `http_request(method="GET", url="http://localhost:8000/")` Let's make sure the steps are detailed enough. Step 3: Write `db.py` with `aiosqlite` connection, table creation (`mappings` with `code` and `url`), and async CRUD functions. Step 4: Write `main.py` with FastAPI app, `/shorten` POST endpoint generating a random code and calling `db.add_mapping`, and `/{code}` GET endpoint returning a 307 redirect using `db.get_url`. Step 5: Write `test_main.py` using `httpx.AsyncClient` to test the `/shorten` and `/{code}` endpoints against a test database. Step 7: Write `Dockerfile` with `FROM python:3.11-slim`, `WORKDIR /app`, `COPY requirements.txt .`, `RUN pip install -r requirements.txt`, `COPY . .`, `CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]`. This looks solid. Let's write it out. 1. `shell(cmd="mkdir -p shortener && cd shortener")` 2. `shell(cmd="python -m venv venv && source venv/bin/activate && pip install fastapi uvicorn aiosqlite pytest httpx")` 3. `write_file(path="shortener/db.py", contents="import aiosqlite\n\nasync def init_db():\n conn = await aiosqlite.connect('shortener.db')\n await conn.execute('CREATE TABLE IF NOT EXISTS mappings (code TEXT PRIMARY KEY, url TEXT)')\n await conn.commit()\n return conn\n\nasync def add_mapping(code, url):\n conn = await init_db()\n await conn.execute('INSERT INTO mappings VALUES (?, ?)', (code, url))\n await conn.commit()\n await conn.close()\n\nasync def get_url(code):\n conn = await init_db()\n cursor = await conn.execute('SELECT url FROM mappings WHERE code = ?', (code,))\n row = await cursor.fetchone()\n await conn.close()\n return row[0] if row else None")` 4. `write_file(path="shortener/main.py", contents="import random\nimport string\nfrom fastapi import FastAPI, HTTPException\nfrom fastapi.responses import RedirectResponse\nfrom db import add_mapping, get_url\n\napp = FastAPI()\n\n@app.post('/shorten')\nasync def shorten(url: str):\n code = ''.join(random.choices(string.ascii_letters + string.digits, k=6))\n await add_mapping(code, url)\n return {'short_url': f'http://localhost:8000/{code}'}\n\n@app.get('/{code}')\nasync def redirect(code: str):\n url = await get_url(code)\n if not url:\n raise HTTPException(status_code=404, detail='Code not found')\n return RedirectResponse(url=url)")` 5. `write_file(path="shortener/test_main.py", contents="import pytest\nimport httpx\nfrom main import app\n\n@pytest.mark.asyncio\nasync def test_shorten_and_redirect():\n async with httpx.AsyncClient(app=app, base_url='http://test') as client:\n resp = await client.post('/shorten', json={'url': 'https://example.com'})\n assert resp.status_code == 200\n code = resp.json()['short_url'].split('/')[-1]\n resp = await client.get(f'/{code}', follow_redirects=False)\n assert resp.status_code == 307")` 6. `shell(cmd="cd shortener && python -m pytest test_main.py")` 7. `write_file(path="shortener/Dockerfile", contents="FROM python:3.11-slim\nWORKDIR /app\nCOPY requirements.txt .\nRUN pip install --no-cache-dir -r requirements.txt\nCOPY . .\nCMD [\"uvicorn\", \"main:app\", \"--host\", \"0.0.0.0\", \"--port\", \"8000\"]")` 8. `shell(cmd="cd shortener && docker build -t shortener-app .")` 9. `shell(cmd="docker run -p 8000:8000 shortener-app")` 10. `http_request(method="POST", url="http://localhost:8000/shorten", body='{"url": "https://example.com"}')` 11. `http_request(method="GET", url="http://localhost:8000/")`