<!-- REASONING (not shown to user) -->
1.  **Analyze the Request:**
    *   Goal: Build and deploy a tiny 'url shortener' web service.
    *   Tools: `shell(cmd)`, `write_file(path, contents)`, `http_request(method, url, body?)`.
    *   Steps required:
        1.  Scaffold FastAPI project in `./shortener`.
        2.  Add `/shorten` POST endpoint and `/{code}` GET redirect.
        3.  Persist mappings in a SQLite DB.
        4.  Run tests with pytest.
        5.  Build and run a Docker image locally.
        6.  Verify with an `http_request`.
    *   Constraints: Numbered plan, specific commands/file paths, no full app code, 20 steps or fewer.

2.  **Drafting the Steps:**

    *   *Step 1: Scaffold the project.*
        *   Need to create the directory and initialize the FastAPI app.
        *   `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy aiosqlite pytest httpx")` (Wait, `aiosqlite` is good for async SQLite, or just `sqlite3` with sync. Let's use `aiosqlite` for better FastAPI integration, or just standard `sqlite3` to keep it simple. Let's stick to standard `sqlite3` and `sqlalchemy` for ORM).
        *   Actually, let's just write the files. The prompt says "scaffold a FastAPI project". I can use `cookiecutter` or just create the files manually. Creating files manually is more reliable with the given tools.
        *   Let's create the directory and install dependencies.
        *   `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`

    *   *Step 2: Write the main application file (FastAPI app, endpoints, SQLite logic).*
        *   `write_file("./shortener/main.py", "...")` (I won't write the full code, just mention the file and what it contains).

    *   *Step 3: Write the test file.*
        *   `write_file("./shortener/test_main.py", "...")`

    *   *Step 4: Write the Dockerfile.*
        *   `write_file("./shortener/Dockerfile", "...")`

    *   *Step 5: Write the docker-compose.yml (optional but good for local running, or just use docker run).*
        *   Let's just use `docker build` and `docker run`.

    *   *Step 6: Run the tests.*
        *   `shell("cd ./shortener && pytest")`

    *   *Step 7: Build the Docker image.*
        *   `shell("cd ./shortener && docker build -t url-shortener .")`

    *   *Step 8: Run the Docker container.*
        *   `shell("docker run -d -p 8000:8000 url-shortener")`

    *   *Step 9: Verify with http_request (POST /shorten).*
        *   `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`

    *   *Step 10: Verify with http_request (GET /{code} - need to get the code from step 9).*
        *   Wait, the prompt says "verify with an http_request". It doesn't strictly say I need to parse the response of step 9 to do step 10, but it's implied to test the redirect. I can just assume a code or do two requests. Let's do two requests to be thorough, or just one if the prompt implies a single verification step. "verify with an http_request" (singular). I'll do the POST, and then a GET to a known code, or just the POST. Let's do both to be safe, or just one combined step. Actually, I can just do the POST and mention the GET. Let's do the POST as the primary verification.

3.  **Refining and Formatting the Steps (aiming for < 20 steps):**

    1.  `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
    2.  `write_file("./shortener/main.py", "FastAPI app with /shorten POST, /{code} GET, and SQLAlchemy SQLite setup")`
    3.  `write_file("./shortener/test_main.py", "Pytest tests using TestClient for /shorten and /{code} endpoints")`
    4.  `write_file("./shortener/Dockerfile", "Dockerfile based on python:3.11-slim, copying requirements and running uvicorn")`
    5.  `shell("cd ./shortener && pytest -v")`
    6.  `shell("cd ./shortener && docker build -t url-shortener .")`
    7.  `shell("docker run -d -p 8000:8000 url-shortener")`
    8.  `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`
    9.  `http_request("GET", "http://localhost:8000/abc123", None)` (Assuming 'abc123' is the returned code, or just a test code).

    Let's make it a bit more detailed to ensure all constraints are met clearly.

    1.  `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
    2.  `write_file("./shortener/main.py", "Code defining FastAPI app, SQLAlchemy SQLite engine, /shorten POST endpoint, and /{code} GET redirect endpoint")`
    3.  `write_file("./shortener/test_main.py", "Pytest code using TestClient to assert /shorten returns a code and /{code} returns a 302 redirect")`
    4.  `write_file("./shortener/Dockerfile", "Dockerfile using python:3.11-slim, installing dependencies, and running uvicorn main:app")`
    5.  `shell("cd ./shortener && pytest -v")`
    6.  `shell("cd ./shortener && docker build -t url-shortener .")`
    7.  `shell("docker run -d -p 8000:8000 url-shortener")`
    8.  `http_request("POST", "http://localhost:8000/shorten", {"url": "https://www.example.com"})`
    9.  `http_request("GET", "http://localhost:8000/<returned_code>", None)`

    Wait, the prompt says "verify with an http_request" (singular). I'll combine the verification into one step or just do the POST. Let's do the POST as it creates the data, and the GET as a second verification step. It's fine to have two http_requests.

    Let's review the constraints:
    - numbered plan
    - shell and tool calls
    - in order
    - (1) scaffold FastAPI in ./shortener
    - (2) add /shorten POST and /{code} GET
    - (3) persist in SQLite
    - (4) run tests with pytest
    - (5) build and run Docker image locally
    - (6) verify with http_request
    - specific commands and file paths
    - no full app code
    - 20 steps or fewer

    Let's refine the steps to be very explicit about the tool calls.

    1. `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
    2. `write_file("./shortener/main.py", "FastAPI app with SQLAlchemy SQLite setup, /shorten POST endpoint, and /{code} GET redirect endpoint")`
    3. `write_file("./shortener/test_main.py", "Pytest tests using TestClient to validate /shorten and /{code} endpoints")`
    4. `write_file("./shortener/Dockerfile", "Dockerfile based on python:3.11-slim, copying app code, installing deps, and running uvicorn")`
    5. `shell("cd ./shortener && pytest -v")`
    6. `shell("cd ./shortener && docker build -t url-shortener .")`
    7. `shell("docker run -d -p 8000:8000 url-shortener")`
    8. `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`
    9. `http_request("GET", "http://localhost:8000/<code_from_step_8>", None)`

    This is 9 steps. Well under 20. Covers all requirements.

    Let's double check if I need to write a `requirements.txt`. It's good practice for Docker.
    Let's add a step for `requirements.txt`.

    1. `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
    2. `write_file("./shortener/requirements.txt", "fastapi\nuvicorn\nsqlalchemy\npytest\nhttpx")`
    3. `write_file("./shortener/main.py", "FastAPI app with SQLAlchemy SQLite setup, /shorten POST endpoint, and /{code} GET redirect endpoint")`
    4. `write_file("./shortener/test_main.py", "Pytest tests using TestClient to validate /shorten and /{code} endpoints")`
    5. `write_file("./shortener/Dockerfile", "Dockerfile based on python:3.11-slim, copying requirements.txt and app code, installing deps, and running uvicorn")`
    6. `shell("cd ./shortener && pytest -v")`
    7. `shell("cd ./shortener && docker build -t url-shortener .")`
    8. `shell("docker run -d -p 8000:8000 url-shortener")`
    9. `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`
    10. `http_request("GET", "http://localhost:8000/<code_from_step_9>", None)`

    This looks solid. It directly maps to the requested steps.
    1 -> scaffold
    2-3 -> add endpoints & persist in SQLite (main.py)
    4 -> tests
    5 -> run tests
    6 -> Dockerfile
    7-8 -> build and run Docker
    9-10 -> verify with http_request

    Let's make sure the tool calls are formatted exactly as requested: `shell(cmd)`, `write_file(path, contents)`, `http_request(method, url, body?)`.

    Step 1: `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
    Step 2: `write_file("./shortener/requirements.txt", "fastapi\nuvicorn\nsqlalchemy\npytest\nhttpx")`
    Step 3: `write_file("./shortener/main.py", "FastAPI app with SQLAlchemy SQLite setup, /shorten POST endpoint, and /{code} GET redirect endpoint")`
    Step 4: `write_file("./shortener/test_main.py", "Pytest tests using TestClient to validate /shorten and /{code} endpoints")`
    Step 5: `write_file("./shortener/Dockerfile", "Dockerfile based on python:3.11-slim, copying requirements.txt and app code, installing deps, and running uvicorn")`
    Step 6: `shell("cd ./shortener && pytest -v")`
    Step 7: `shell("cd ./shortener && docker build -t url-shortener .")`
    Step 8: `shell("docker run -d -p 8000:8000 url-shortener")`
    Step 9: `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`
    Step 10: `http_request("GET", "http://localhost:8000/<code_from_step_9>", None)`

    Looks perfect. Simple, methodical, follows all constraints.

<!-- ANSWER -->
1. `shell("mkdir -p ./shortener && cd ./shortener && pip install fastapi uvicorn sqlalchemy pytest httpx")`
2. `write_file("./shortener/requirements.txt", "fastapi\nuvicorn\nsqlalchemy\npytest\nhttpx")`
3. `write_file("./shortener/main.py", "FastAPI app with SQLAlchemy SQLite setup, /shorten POST endpoint, and /{code} GET redirect endpoint")`
4. `write_file("./shortener/test_main.py", "Pytest tests using TestClient to validate /shorten and /{code} endpoints")`
5. `write_file("./shortener/Dockerfile", "Dockerfile based on python:3.11-slim, copying requirements.txt and app code, installing deps, and running uvicorn")`
6. `shell("cd ./shortener && pytest -v")`
7. `shell("cd ./shortener && docker build -t url-shortener .")`
8. `shell("docker run -d -p 8000:8000 url-shortener")`
9. `http_request("POST", "http://localhost:8000/shorten", {"url": "https://example.com"})`
10. `http_request("GET", "http://localhost:8000/<code_from_step_9>", None)`