---
name: bare-os-super-developer
version: 1.0.0
description: Write Bare OS scripts and small apps using ctx — VFS, execLine, hooks, caps, and safe patterns (no Node in /bin/agent loop).
tags: [bare-os, ctx, scripts, vfs, kernel, developer]
requires: [read_file, read_proc_file, run_js_script]
---

# bare-os-super-developer — Scripts, apps, and `ctx`

## When to use

Use this skill when you (or the user) need to **author or debug** Bare OS **JavaScript** that runs **inside the guest** (kernel init, `/bin/*` utilities, `kernel.ext.d`, user `.mjs` run via **`run_js_script`**, or Pear/booter-hosted scripts). It complements repo docs: treat **`developer-guide/02-the-context-object.md`** and **`packages/bare-os-booter/lib/ctx/bare-os-ctx.d.ts`** as the canonical deep dives; this file is the **fast mental model**.

## Core model

1. **Entrypoints** — Kernel: **`async function start(ctx)`** in `/boot/init.js` (or your image). Commands: **`async function run(ctx, argv)`** where **`argv[0]`** is the invoked name (e.g. `agent`). You **must** set **`ctx.exitCode`** (number) before returning on failure paths.
2. **`ctx` is not Node** — There is no full **`process`**, no **`require('node:fs')`**. The booter assembles **`ctx`** as the narrow **syscall surface**: **`vfs`**, **`env`**, **`execLine`**, **`runBinCommand`**, optional **`httpFetch`**, **`bare`**, identity helpers, diagnostics, etc. See the mermaid overview in Chapter 2 of the developer guide.
3. **`/bin/agent` is special** — The agent bundle uses **`run_js_script`** for guest JS and a frozen tool surface; do not assume **`node`** exists. For **general** in-guest scripting, prefer **`ctx.vfs`** + **`ctx.execLine`** / **`ctx.runBinCommand`** and optional `**ctx.bare.*`** modules when enabled.

## Writing scripts (`run(ctx, argv)`)

- **Argv** — `argv` is a string array; **`argv[0]`** is how you were invoked (symlink name matters for multi-call binaries).
- **Stdout** — Prefer **`ctx.console.log`** / **`ctx.console.error`** (session-aware). For binary or captured stdout, **`ctx.bareOsBinWrite`** may exist when the shell captures pipeline output.
- **Shell a subprocess** — **`await ctx.execLine('some shell line', { signal, timeoutMs })`** returns a string (see booter **`raceWithAbortAndTimeout`**). Heavy work: `**await ctx.runBinCommand(['/bin/grep', …], opts)`** for same resolution as the interactive shell.
- **Filesystem** — **`await ctx.vfs.readFile(path)`** → **`Uint8Array`**; **`await ctx.vfs.writeFile(path, buf, opts?)`**. Decode with **`ctx.b4a.toString(buf)`** or **`TextDecoder`**. Always use **absolute** paths under **`/home`**, **`/tmp`**, **`/mnt`**, **`/bin`**, etc., per policy.
- **Environment** — **`ctx.env`** is mutable shell state (also **`ctx.vfs.env`**). After **`execLine`**, **`ctx.env.BARE_OS_EXIT_STATUS`** reflects last exit code when the booter sets it.
- **Exit** — Set **`ctx.exitCode = 1`** (or other code) on error; **`0`** on success. **`ctx.requestBooterExit(code)`** ends the whole session from builtins like **`exit`**.

## Building “apps” (long-lived behaviour)

Think in layers the stock OS already uses:

| Layer | Mechanism | Notes |
| --- | --- | --- |
| **Init** | **`bareOsRegisterBootStepHook`**, initd units | Boot-order DAG (stock: **`bare-os-www`** before **`bare-holesail`** so **`bare-www-*`** reaches loopback HTTP; **`bare-openssh`** + login stack ensure **`bare-ssh-*`** in **`~/.holesail/state.json`**); pair **`registerKernelShutdownHook`** / initd disposers for teardown. |
| **Virtual files** | **`bareOsRegisterVirtualFile(name, reader, opts?)`** | Serves **`/run/bare-os/virtual/<name>`**; gated by runtime caps. |
| **IPC** | **`ctx.bareOsIpc`** when present | `**push`/`take**`, JSON helpers, fanout, duplex bridge — bounded; audit when `**BARE_OS_IPC_AUDIT=1`**. |
| **Kernel extensions** | **`bareOsRegisterKernelExtensionRecord`**, **`bareOsRunImageScript`** under **`/lib/bare-os/extensions/`** | Trusted image paths only. |
| **Sandboxed user JS** | **`bareOsSandboxRunScript(source, argv?, opts?)`** | Restricted **`ctx`**; disable with `**BARE_OS_SANDBOX_SCRIPT=0`**. |
| **Pear / host** | **`bareOsPearIpcEmit`**, **`bareOsPearIpcRequest`**, mirror/export hints | Host must cooperate; return `**{ ok, hint }`** patterns. |

Before touching sensitive **`ctx`** methods in hardened images, call **`ctx.bareOsIsCtxMethodAllowed?.(name)`** when boot policy **`BARE_OS_BOOT_POLICY_ALLOWED_CTX_METHODS`** is set.

## `ctx` field map (cheat sheet)

**Always read live truth** for capability bits: **`read_proc_file`** on **`/proc/bare_os/features`** and **`/proc/bare_os/capabilities.json`** — do not infer from man pages alone (see **`bare-os-kernel-proc`** skill).

### Files, drives, process

- **`ctx.vfs`** — **`readFile`**, **`writeFile`**, **`mkdir`**, **`readdir`**, `**stat`/`lstat**`, **`chmod`**, … Path routing: system vs **personal** Hyperdrive; **`ctx.drive`** vs **`ctx.personalDrive`** for advanced use.
- **`ctx.env`**, **`ctx.drive`**, **`ctx.personalDrive`**, **`ctx.disk`** — Session identity and mounts.
- **`ctx.execLine`**, **`ctx.runBinCommand`** — Shell and `/bin` execution with shared policy (timeouts, abort).

### Bytes, console, session

- **`ctx.b4a`** — Buffer/string helpers for Hyperdrive payloads.
- **`ctx.console`**, **`ctx.readLine`**, **`ctx.writeScreen`** — REPL session ( **`readLine`** may be Fish-backed when enabled).
- **`ctx.exitCode`**, **`ctx.requestBooterExit`**, **`ctx.registerKernelShutdownHook`**

### Bare OS introspection & policy

- **`ctx.bareOsCtxApiVersion`**, **`ctx.bareOsRuntimeCaps`** (frozen)
- **`ctx.bareOsAdvertisedKernelCapabilityWords`**, **`ctx.bareOsSeedKernelCapabilityWords`** — `**>>> 0`** when testing bits.
- **`ctx.bareOsGetResourceStatus`**, **`ctx.bareOsReadProcMetricsLive`**, **`ctx.bareOsReadBareTopSnapshot`**
- **`ctx.bareOsRegisterVirtualFile`**, **`ctx.bareOsInvalidateVirtualFile`**, **`ctx.bareOsUpdateVirtualFileMeta`**
- **`ctx.bareOsEmitIpcAudit`**, **`ctx.bareOsEvaluatePeerAdmission`**, **`ctx.bareOsEmitMirrorDriveHint`**

### Optional / host-dependent

- **`ctx.httpFetch`** — Same allow/deny policy as **`curl`** / **`wget`**; every host for **`web_fetch`** must be allowlisted.
- **`ctx.bare`** — Frozen map of vendored modules (**`b4a`**, **`protomux`**, …) when **`BARE_OS_BARE_MODULES`** allows.
- **`ctx.bareOsHostStats`**, `**ctx.bareOsChat***`, `**ctx.bareOsPearIpc*`** — Present only when wired by the booter/host.

For the **full** list and semantics, open **`developer-guide/02-the-context-object.md`** in the repo (or **`read_file`** on a mounted checkout).

## Minimal script template (guest)

```js
/**
 * @param {Record<string, unknown>} ctx
 * @param {string[]} argv
 */
export async function run(ctx, argv) {
  const argv0 = argv[0] || 'script'
  const vfs = ctx.vfs
  if (!vfs?.readFile) {
    ctx.console.error(argv0 + ': no vfs')
    ctx.exitCode = 1
    return
  }
  try {
    const buf = await vfs.readFile('/proc/bare_os/features.json')
    const t =
      ctx.b4a && typeof ctx.b4a.toString === 'function'
        ? ctx.b4a.toString(buf)
        : new TextDecoder().decode(buf)
    ctx.console.log(t.slice(0, 500))
  } catch (e) {
    ctx.console.error(argv0 + ': ' + (e && e.message ? e.message : String(e)))
    ctx.exitCode = 1
  }
}
```

Save under **`/home/.../my-tool.mjs`** and run by **absolute path** (or register under **`/bin`** on the image). **Do not** rely on **`node`** in the guest.

## Agent-specific note

When helping **inside `/bin/agent`**, the model uses **tools** (`read_file`, `run_js_script`, …) backed by the **same** personal/system VFS as the rest of the guest. **`run_js_script`** writes a temp **`.mjs`** under **`~/.agent/**` and executes it like a **`/bin`** script — the script body should use the same **`ctx`** patterns above when the harness passes **`ctx`**.

## Checklist before shipping

1. **`read_proc_file`** / **`get_system_info`** — confirm needed **features** and **caps** exist this session.
2. **Paths** — absolute, no **`..`** escape from allowed roots.
3. **Timeouts** — pass **`AbortSignal`** / **`timeoutMs`** to **`execLine`** / **`readLine`** for network or slow FS.
4. **Teardown** — unregister hooks, clear intervals, dispose IPC fanout subscribers.
5. **Secrets** — never log **`~/.agent/config.json`** or keys; redact in **`MEMORY.md`**.

## Output format (when this skill was used)

- **What you read** — which **`ctx`** fields or **`/proc`** files grounded the answer.
- **Plan** — file paths, entrypoint (`run` vs `start`), and exit semantics.
- **Risks** — policy gates, missing caps, host-only APIs.