Add per-user config system with sandlot config command

Allow users to configure container memory limit (default 32G) via
`sandlot config memory <value>` instead of hardcoding it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -36,7 +36,9 @@ src/
   fmt.ts        # ANSI escape codes, die/success/info helpers, pager
   markdown.ts   # Terminal markdown renderer (headings, bold, links, code blocks)
   spinner.ts    # CLI progress spinner (braille frames)
+  config.ts     # Per-user config (~/.config/sandlot/config.json): memory, etc.
   commands/
+    config.ts   # Get/set config values (e.g. `sandlot config memory 16G`)
     new.ts      # Create session, derive branch name from prompt
     open.ts     # Re-enter existing session (always uses --continue)
     close.ts    # Remove worktree and clean up session
@@ -79,7 +81,7 @@ Each module has a single responsibility. No classes — only exported async func
 
 - Image: `ubuntu:24.04`
 - User: `ubuntu`
-- Memory limit: 4G
+- Memory limit: configurable via `sandlot config memory` (default 32G)
 - Mounts: `~/dev` **read-only** at `/host`, `~/.sandlot` read-write at `/sandlot`
 - Host symlinks: creates `~/dev` → `/host` and `~/.sandlot` → `/sandlot` inside the container so host-absolute worktree paths resolve correctly
 - `containerPath()` in `vm.ts` translates host paths to container paths (`~/.sandlot/…` → `/sandlot/…`, `~/dev/…` → `/host/…`)

src/cli.ts

@@ -26,6 +26,7 @@ import { register as registerVmCommands } from "./commands/vm.ts"
 import { action as completionsAction } from "./commands/completions.ts"
 import { action as initAction } from "./commands/init.ts"
 import { action as cdAction } from "./commands/cd.ts"
+import { action as configAction } from "./commands/config.ts"
 
 const pkg = await Bun.file(new URL("../package.json", import.meta.url)).json()
 
@@ -185,6 +186,12 @@ program
 
 program.commandsGroup("Admin Commands:")
 
+program
+  .command("config")
+  .argument("[args...]", "key [value]")
+  .description("Get or set configuration (e.g. sandlot config memory 16G)")
+  .action(configAction)
+
 program
   .command("cleanup")
   .description("Remove stale sessions whose worktrees no longer exist")

src/commands/config.ts

@@ -0,0 +1,38 @@
+import { die } from "../fmt.ts"
+import * as config from "../config.ts"
+
+const KEYS: Record<string, { description: string; validate: (v: string) => string | null }> = {
+  memory: {
+    description: "Container memory limit (e.g. 4G, 16G, 32G, 64G)",
+    validate: (v) => /^\d+[GMgm]$/.test(v) ? null : "Must be a number followed by G or M (e.g. 16G)",
+  },
+}
+
+export async function action(args: string[]) {
+  if (args.length === 0) {
+    const cfg = await config.load()
+    const defaults: Record<string, string> = { memory: "32G" }
+    for (const [key, meta] of Object.entries(KEYS)) {
+      const val = (cfg as any)[key]
+      const display = val ?? `${defaults[key]} (default)`
+      console.log(`${key} = ${display}`)
+    }
+    return
+  }
+
+  if (args.length === 1) {
+    const key = args[0]
+    if (!(key in KEYS)) die(`Unknown config key: ${key}\nAvailable keys: ${Object.keys(KEYS).join(", ")}`)
+    const val = await config.get(key as keyof config.Config)
+    const defaults: Record<string, string> = { memory: "32G" }
+    console.log(val ?? `${defaults[key]} (default)`)
+    return
+  }
+
+  const [key, value] = args
+  if (!(key in KEYS)) die(`Unknown config key: ${key}\nAvailable keys: ${Object.keys(KEYS).join(", ")}`)
+  const error = KEYS[key].validate(value)
+  if (error) die(error)
+  await config.set(key as keyof config.Config, value.toUpperCase())
+  console.log(`${key} = ${value.toUpperCase()}`)
+}

src/config.ts

@@ -0,0 +1,33 @@
+import { homedir } from "os"
+import { dirname, join } from "path"
+
+const CONFIG_PATH = join(homedir(), ".config", "sandlot", "config.json")
+
+export interface Config {
+  memory?: string
+}
+
+export async function load(): Promise<Config> {
+  try {
+    return await Bun.file(CONFIG_PATH).json()
+  } catch {
+    return {}
+  }
+}
+
+export async function save(config: Config): Promise<void> {
+  const { mkdir } = await import("fs/promises")
+  await mkdir(dirname(CONFIG_PATH), { recursive: true })
+  await Bun.write(CONFIG_PATH, JSON.stringify(config, null, 2) + "\n")
+}
+
+export async function get<K extends keyof Config>(key: K): Promise<Config[K]> {
+  const config = await load()
+  return config[key]
+}
+
+export async function set<K extends keyof Config>(key: K, value: Config[K]): Promise<void> {
+  const config = await load()
+  config[key] = value
+  await save(config)
+}

src/vm.ts

@@ -4,6 +4,7 @@ import { homedir } from "os"
 import { dirname, join } from "path"
 import { requireApiKey } from "./env.ts"
 import { info } from "./fmt.ts"
+import { get as getConfig } from "./config.ts"
 
 const DEBUG = !!process.env.DEBUG
 const CONTAINER_NAME = "sandlot"
@@ -66,7 +67,8 @@ function hostMounts(home: string): { dev: boolean; code: boolean } {
 /** Pull the image and start the container in detached mode. */
 async function createContainer(home: string): Promise<void> {
   const mounts = hostMounts(home)
-  const args = ["container", "run", "-d", "--name", CONTAINER_NAME, "-m", "32G"]
+  const memory = (await getConfig("memory")) ?? "32G"
+  const args = ["container", "run", "-d", "--name", CONTAINER_NAME, "-m", memory]
   if (mounts.dev) args.push("--mount", `type=bind,source=${home}/dev,target=/host/dev,readonly`)
   if (mounts.code) args.push("--mount", `type=bind,source=${home}/code,target=/host/code,readonly`)
   args.push("-v", `${home}/.sandlot:/sandlot`, "ubuntu:24.04", "sleep", "infinity")