Demo 5 Sandbox Feature Pr

---
name: demo-5-sandbox-feature-pr
description: Demo skill for the meta "decode improves decode" flow — launch decode in a sandboxed clone of the course repo, plan and build one small feature inside the Workspace, let Hand-back push the Session Branch, then open a draft PR against the course repo.
---

The meta demo: **decode improves decode.** Run decode inside an isolated sandbox Workspace that is
a clone of this very course repo, plan and implement one small self-contained feature there, and
let the harness ship the work back as a branch you turn into a draft PR.

Nothing the model does touches your host checkout — the Workspace is an isolated clone, and the
branch only lands on your host through Hand-back (ADR-0012 §8).

## 1. Launch decode against a sandboxed clone of the course repo (human step)

Sandbox mode is selected by the **`SANDBOX_MODE` environment variable** — it is an env var, not a
command-line flag; the repo to clone into the Workspace is the **`--repo`** flag. Launch the local
docker rung (Docker must be running):

```
SANDBOX_MODE=docker decode --repo git@github.com:decodingai-magazine/building-a-coding-agent-from-scratch-course.git
```

This clones the course repo into the isolated Workspace (`/workspace` ≡ host `.decode/sandbox`)
and drops you into the REPL, with `bash` and the file tools scoped to that clone.

To run the same demo on the remote rung instead, swap `SANDBOX_MODE=docker` for
`SANDBOX_MODE=modal` — everything else is identical (Modal credentials must be configured).

## 2. Plan the feature — in plan mode

If you are decode reading this inside the Workspace, start here — step 1 is the human's launch
command, already done; do NOT try to run `decode` yourself. Enter **plan mode** by calling
`enter_plan_mode` with **no arguments** (it takes none — you present the plan later, to
`exit_plan_mode`), explore the code read-only, then present a short plan before touching anything.
Pick ONE feature — small, self-contained, provable in a single session:

- A `decode --version` flag that prints the installed package version, plus its unit test.
- One small pure helper (e.g. in `tools/` or `entities/`) with a focused unit test.
- A scoped docstring/README fix that resolves a real inaccuracy you found while exploring.

The plan should name the files to touch, the test that proves the feature, and nothing else.
Exit plan mode (`exit_plan_mode`) once the human approves it.

## 3. Build it inside the Workspace

Implement the plan: edit, then run the suite inside the Workspace (`uv run pytest -q` /
`make unit-tests`) until it is green. Keep the final green test output — it goes in the PR body.
All of this happens on the sandboxed clone.

## 4. Get the branch onto the remote

The branch has to be on `origin` before a PR can point at it. There are two ways it gets there —
know which one you are in:

- **Sandbox run (the intended demo, `SANDBOX_MODE=docker`/`modal`):** just leave the REPL (exit,
  or `/ship` while idle). On exit, **Hand-back** secures the final Workspace onto a deterministic
  `decode/<session-id>` **Session Branch**, auto-commits any uncommitted model work, and
  `git push`es it back to the course repo with your ambient host git credentials — every git
  command runs host-side, so no credential ever enters the sandbox. The friendly exit line names
  the branch it pushed. You do **not** push by hand in this path.

- **No sandbox, or your own feature branch:** if decode is running straight on the host (no
  `SANDBOX_MODE`), there is no Hand-back — commit your work on a feature branch and push it
  yourself:

  ```
  git push -u origin <your-branch>
  ```

  **Give this push a generous timeout (≥ 180s) and do not kill it.** This repo installs a
  **pre-push** hook that runs the full unit suite (`make unit-tests`, ~2 minutes) before the push
  goes out — a short tool timeout will terminate it mid-run and look like a network hang. It is
  the gate doing its job; you already ran the suite green in step 3, so just let it finish. Do
  **not** reach for `git push --no-verify` to dodge it — that skips the format/lint/test gate the
  push is supposed to enforce. Only fall back to `--no-verify` if the human explicitly tells you
  to.

## 5. Open a draft PR against the course repo

Turn the pushed branch into a draft PR with the `gh` CLI — `--head decode/<session-id>` for the
Hand-back path, or `--head <your-branch>` for the manual path. Build the body with a heredoc so
newlines and backticks land literally (never hand-escape `\n` into `--body`):

~~~
gh pr create --draft \
  --repo decodingai-magazine/building-a-coding-agent-from-scratch-course \
  --head <branch> --title "<feature>" \
  --body "$(cat <<'EOF'
<what & why, 2-3 lines>

Test evidence:
```
<the green pytest summary line>
```

Built end-to-end inside a decode sandbox Workspace (SANDBOX_MODE=docker) and shipped by Hand-back.
EOF
)"
~~~

Report the feature you built, the branch it landed on, and the draft-PR URL.