feat(sandbox): run the guest server as an unprivileged user

CHANGELOG.md

@@ -9,6 +9,12 @@ file is the human-readable summary of what changed and why.
 
 ### Desktop / Web UI
 
+- **Sandboxes run the agent as an unprivileged user** — the server inside a
+  sandbox no longer runs as root: it drops to the image's ordinary `codev`
+  account once the guest has finished mounting, so a sandbox escape has one
+  less privilege to work with. Project files, the guest home, and the bundled
+  skills all remain fully usable. On macOS this takes effect with the next
+  published sandbox image; Windows sandboxes pick it up immediately.
 - **Per-sandbox CPU and memory limits (macOS)** — the Add sandbox dialog gains
   optional CPUs and Memory fields, applied when the sandbox VM boots; leaving
   them empty keeps the previous defaults (4 CPUs, 4 GB). The fields appear

packages/codev-sandbox/image/guest/codev-init

@@ -34,8 +34,17 @@ for (const [key, value] of Object.entries(boot.env)) console.log("export " + key
 
 export HOME=/home/codev
 cp -Rn /etc/skel/. "$HOME"/ 2>/dev/null || true
+
+# The server runs as the image's unprivileged codev user; PID 1 and the vsock
+# bridges stay root. No uid remapping is needed: Virtualization.framework's
+# virtio-fs performs host operations as the process that owns the VM and
+# reports every shared file as root inside the guest, so guest ownership never
+# gates workspace access — verified on macOS 15 (append, mkdir, create all
+# succeed as uid 1000 and land on the host owned by the host user).
+chown -R codev:codev "$HOME" 2>/dev/null
+
 cd /workspace
-node /opt/codev-guest/server-launch.mjs &
+setpriv --reuid=codev --regid=codev --init-groups node /opt/codev-guest/server-launch.mjs &
 SERVER=$!
 
 # Stay PID 1: reap orphans, power off when the server dies so the helper's

packages/codev-sandbox/src/wsl/provider.test.ts

@@ -35,8 +35,14 @@ if (args[0] === "--unregister") {
 }
 if (args.includes("wslpath")) { process.stdout.write("/mnt/hostpath\\n"); process.exit(0) }
 
-// Boot command: assert the script the provider built, then answer health checks.
 const script = args[args.length - 1]
+// Import-time distro configuration runs through the same -- /bin/sh -c shape.
+if (script.includes("/etc/wsl.conf")) {
+  const value = read(); value.wslConf = script; write(value)
+  process.exit(0)
+}
+
+// Boot command: assert the script the provider built, then answer health checks.
 if (!script.includes("mount --bind") || !script.includes("server-launch.mjs")) {
   process.stderr.write("unexpected boot script\\n"); process.exit(2)
 }
@@ -208,6 +214,26 @@ test("egress wires the broker bridge, guest config, and CODEV_CONFIG", async ()
   await rm(dir, { recursive: true, force: true })
 })
 
+test("configures automount at import and runs the server unprivileged", async () => {
+  const dir = await mkdtemp(join(tmpdir(), "wsl-test-"))
+  const provider = createWslProvider(await preparedOptions(dir))
+  await provider.create(config)
+  const imported = JSON.parse(await Bun.file(join(dir, "state.json")).text())
+  // Windows has no uid to match, so the guest's own codev user owns the
+  // automounted drives — otherwise the dropped server cannot write them.
+  expect(imported.wslConf).toContain("uid=1000,gid=1000")
+
+  const sandbox = await provider.start(config)
+  const state = JSON.parse(await Bun.file(join(dir, "state.json")).text())
+  expect(state.bootScript).toContain("setpriv --reuid=codev --regid=codev --init-groups node")
+  // Root still does the mounts and the bridge before dropping.
+  expect(state.bootScript.indexOf("mount --bind")).toBeLessThan(state.bootScript.indexOf("setpriv"))
+
+  sandbox.stop()
+  await provider.destroy(config)
+  await rm(dir, { recursive: true, force: true })
+})
+
 test("routeless egress still injects the guest config but starts no broker", async () => {
   const dir = await mkdtemp(join(tmpdir(), "wsl-test-"))
   const provider = createWslProvider(

packages/codev-sandbox/src/wsl/provider.ts

@@ -129,6 +129,25 @@ export function createWslProvider(options: WslProviderOptions): SandboxProvider
     })
     if (imported.code !== 0)
       throw new Error(`wsl --import failed for ${distro}: ${imported.stderr.trim() || `exited ${imported.code}`}`)
+    // Windows has no uid to match, so the guest keeps its own codev user and
+    // the Windows drives are automounted as that user — without this the
+    // unprivileged server could not write the project directory. wsl.conf is
+    // read at distro boot, so write it and terminate before the first start.
+    const configured = await wsl([
+      "-d",
+      distro,
+      "-u",
+      "root",
+      "--",
+      "/bin/sh",
+      "-c",
+      `printf '[automount]\\noptions = "metadata,uid=1000,gid=1000"\\n' > /etc/wsl.conf`,
+    ])
+    if (configured.code !== 0)
+      throw new Error(
+        `could not write /etc/wsl.conf in ${distro}: ${configured.stderr.trim() || `exited ${configured.code}`}`,
+      )
+    await wsl(["--terminate", distro])
     await writeImageMarker(dirs.base, asset)
   }
 
@@ -191,6 +210,7 @@ export function createWslProvider(options: WslProviderOptions): SandboxProvider
           ? [`mount --bind ${shellQuote(await guestPath(distro, configDir))} /codev-config`]
           : []),
         `cp -Rn /etc/skel/. "$HOME"/ 2>/dev/null || true`,
+        `chown -R codev:codev "$HOME" 2>/dev/null || true`,
         `if [ -f /etc/codev-guest.env ]; then . /etc/codev-guest.env; fi`,
         // Guest loopback 8788 is the broker stub on every backend; on WSL it
         // relays to the host's TCP broker at the NAT gateway.
@@ -201,7 +221,10 @@ export function createWslProvider(options: WslProviderOptions): SandboxProvider
             ]
           : []),
         `cd ${shellQuote(await guestPath(distro, config.projectDir))}`,
-        `exec node ${SANDBOX_GUEST_LAUNCHER}`,
+        // Root did the bind mounts and the socat bridge; the agent itself runs
+        // as the image's unprivileged codev user, which owns the automounted
+        // Windows drives per the wsl.conf written at import.
+        `exec setpriv --reuid=codev --regid=codev --init-groups node ${SANDBOX_GUEST_LAUNCHER}`,
       ].join("\n")
 
       const child = spawnImpl(