--- name: decodingai-magazine-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." license: "Apache-2.0" metadata: decimalai-skill-id: "7a79c5f8-84de-4af7-ab8b-3ea48eb0b54a" decimalai-version-id: "313cb156-91f4-4b50-89c5-6542ab03e0c1" decimalai-version: "1" decimalai-body-sha256: "b89c375cde1fadb7708dd336057d6e9c92c4d58e4460e85ab32895e111f7532f" decimalai-name: "decodingai-magazine/demo-5-sandbox-feature-pr" decimalai-format: "1" decimalai-invocation: "model" decimalai-source: "https://app.decimal.ai/s/decodingai-magazine-demo-5-sandbox-feature-pr@1/SKILL.md" --- 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 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 ``` **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/` for the Hand-back path, or `--head ` 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 --title "" \ --body "$(cat <<'EOF' Test evidence: ``` ``` 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.