# Build A Runtime With A Custom Delegate

This tutorial builds a runtime whose pass-through command is `python` instead of
`conda`.

You will still include conda, conda-rattler-solver, and conda-spawn in the
managed prefix because those packages are part of conda-ship's runtime contract.
The difference is the command users get after bootstrap: unknown runtime
arguments are passed to Python.

## Before You Start

Install conda-ship and either conda-workspaces or Pixi:

::::{tab-set}

:::{tab-item} conda-workspaces

```bash
conda create -n cs-python-demo -c conda-forge python pip conda-workspaces
conda activate cs-python-demo
python -m pip install conda-ship
```

:::

:::{tab-item} Pixi

```bash
conda create -n cs-python-demo -c conda-forge python pip pixi
conda activate cs-python-demo
python -m pip install conda-ship
```

:::

::::

## Create The Project

Create a project directory:

```bash
mkdir python-runtime
cd python-runtime
```

::::{tab-set}

:::{tab-item} conda-workspaces

```bash
conda workspace init --format conda --name python-runtime
conda workspace add --feature ship --no-lockfile-update \
  "python>=3.12" \
  "conda>=25.1" \
  conda-rattler-solver \
  "conda-spawn>=0.1.0"
```

Add conda-ship policy:

```bash
cat >> conda.toml <<'TOML'

[tool.conda-ship]
runtime = "pydemo"
runtime-version = "0.1.0"
delegate = "python"
layout = "online"
source-environment = "ship"
exclude = ["conda-libmamba-solver"]
TOML
```

Lock it:

```bash
conda workspace lock
```

:::

:::{tab-item} Pixi

```bash
pixi init --channel conda-forge
cat >> pixi.toml <<'TOML'

[feature.ship.dependencies]

[environments]
ship = { features = ["ship"], no-default-feature = true }

[tool.conda-ship]
runtime = "pydemo"
runtime-version = "0.1.0"
delegate = "python"
layout = "online"
source-environment = "ship"
exclude = ["conda-libmamba-solver"]
TOML
pixi add --feature ship --no-install \
  "python>=3.12" \
  "conda>=25.1" \
  conda-rattler-solver \
  "conda-spawn>=0.1.0"
pixi lock
```

:::

::::

## Build It

Run a preflight, then build:

```bash
cs inspect
cs build
```

The runtime is staged as `dist/pydemo` on Unix and `dist/pydemo.exe` on Windows.

## Bootstrap It

Use a temporary install path for the tutorial:

```bash
mkdir -p .tmp
./dist/pydemo --path "$PWD/.tmp/pydemo" bootstrap
```

The runtime installs the selected source environment into the managed prefix.
Even though the delegate is Python, the prefix still contains conda and
conda-spawn.

## Run Python Through The Runtime

Create a small script:

```bash
cat > hello.py <<'PY'
import sys

print("hello from", sys.executable)
PY
```

Run it through the runtime:

```bash
./dist/pydemo --path "$PWD/.tmp/pydemo" hello.py
```

`pydemo` bootstraps or reuses its managed prefix, prepares the delegate
environment, and passes `hello.py` to the `python` executable inside that
prefix.

## Clean Up

Remove the tutorial install path:

```bash
./dist/pydemo --path "$PWD/.tmp/pydemo" uninstall --yes
```

## What You Learned

The `delegate` is the executable that receives pass-through arguments after the
runtime is bootstrapped. Use `delegate = "conda"` for conda-like distributions,
and another executable when the runtime should present a smaller or different
command surface.