fix(sandbox): keep vz sockets inside the AF_UNIX path limit

packages/codev-sandbox/src/socket.test.ts

@@ -0,0 +1,20 @@
+import { expect, test } from "bun:test"
+import { join } from "node:path"
+import { SANDBOX_SUN_PATH_MAX, sandboxSocketDir } from "./socket"
+
+// The failure this guards against is silent: an over-long AF_UNIX path is
+// truncated at bind time, so the socket appears where nobody is listening.
+test("socket paths stay inside the AF_UNIX limit for realistic sandbox names", () => {
+  const appData = "/Users/someone/Library/Application Support/ai.opencode.desktop.dev/sandboxes"
+  for (const name of ["a", "codev-work", "a-rather-long-sandbox-name-someone-might-type"]) {
+    for (const file of ["server.sock", "broker.sock"]) {
+      const path = join(sandboxSocketDir(join(appData, name)), file)
+      expect(path.length).toBeLessThanOrEqual(SANDBOX_SUN_PATH_MAX)
+    }
+  }
+})
+
+test("each sandbox gets its own socket directory", () => {
+  expect(sandboxSocketDir("/data/one")).not.toBe(sandboxSocketDir("/data/two"))
+  expect(sandboxSocketDir("/data/one")).toBe(sandboxSocketDir("/data/one"))
+})

packages/codev-sandbox/src/socket.ts

@@ -0,0 +1,25 @@
+import { createHash } from "node:crypto"
+import { mkdir } from "node:fs/promises"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+
+// AF_UNIX paths are capped at 104 bytes on macOS (108 on Linux) — and the
+// limit is enforced by silent truncation, so an over-long path binds
+// somewhere unintended and the peer then fails with ENOENT. The app's data
+// directory alone is ~74 characters, so a sandbox named "codev-work" already
+// overflows. Sockets therefore live under a short per-user directory keyed by
+// a hash of the sandbox's data dir, which keeps them unique per sandbox and
+// well clear of the limit.
+export const SANDBOX_SUN_PATH_MAX = 103
+
+export function sandboxSocketDir(sandboxDir: string) {
+  return join(tmpdir(), `codev-sbx-${createHash("sha256").update(sandboxDir).digest("hex").slice(0, 10)}`)
+}
+
+export async function createSandboxSocketDir(sandboxDir: string) {
+  const dir = sandboxSocketDir(sandboxDir)
+  // 0700: on Linux the system temp dir is shared, so the sockets inside must
+  // not be reachable by other users.
+  await mkdir(dir, { recursive: true, mode: 0o700 })
+  return dir
+}

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

@@ -8,6 +8,7 @@ import { runCommand, unpackRootfs } from "../bwrap/rootfs"
 import { readImageMarker, stageAsset, writeImageMarker } from "../image"
 import type { SandboxAsset } from "../manifest"
 import { macosSandboxAvailability } from "../policy"
+import { createSandboxSocketDir } from "../socket"
 import type { SandboxAvailability, SandboxConfig, SandboxJobOptions, SandboxProvider } from "../provider"
 import { createVzHelperEventReader, type VzHelperEvent, type VzVmConfig } from "./protocol"
 
@@ -123,6 +124,9 @@ export function createVzProvider(options: VzProviderOptions): SandboxProvider {
       await rm(dirs.runtime, { recursive: true, force: true })
       await mkdir(dirs.runtime, { recursive: true })
       await mkdir(dirs.guestConfig, { recursive: true })
+      // Sockets live outside the data dir: their absolute path must fit the
+      // AF_UNIX limit, which the data dir alone nearly exhausts.
+      const socketDir = await createSandboxSocketDir(dirs.base)
 
       // The broker must be listening before guest traffic flows: codev-vmm
       // dials runtime/broker.sock per guest connection and refuses when
@@ -133,7 +137,7 @@ export function createVzProvider(options: VzProviderOptions): SandboxProvider {
       const broker = egress?.routes.length
         ? createBrokerServer({ routes: egress.routes, fetchImpl: egress.fetchImpl ?? fetchImpl, auth: egress.auth })
         : null
-      if (broker) await broker.listenUnix(join(dirs.runtime, "broker.sock"))
+      if (broker) await broker.listenUnix(join(socketDir, "broker.sock"))
       if (egress?.guestConfig) await writeFile(join(dirs.guestConfig, "codev.json"), egress.guestConfig)
 
       const credentials = generateSandboxCredentials()
@@ -147,7 +151,7 @@ export function createVzProvider(options: VzProviderOptions): SandboxProvider {
           },
         }),
       )
-      const serverSocket = join(dirs.runtime, "server.sock")
+      const serverSocket = join(socketDir, "server.sock")
       const initrd = await stat(join(dirs.image, VZ_INITRD_FILE)).catch(() => null)
       const vmConfig: VzVmConfig = {
         kernel: join(dirs.image, VZ_KERNEL_FILE),
@@ -164,7 +168,7 @@ export function createVzProvider(options: VzProviderOptions): SandboxProvider {
         ],
         forwards: [
           { direction: "host-to-guest", vsockPort: VZ_SERVER_VSOCK_PORT, socketPath: serverSocket },
-          { direction: "guest-to-host", vsockPort: VZ_BROKER_VSOCK_PORT, socketPath: join(dirs.runtime, "broker.sock") },
+          { direction: "guest-to-host", vsockPort: VZ_BROKER_VSOCK_PORT, socketPath: join(socketDir, "broker.sock") },
         ],
       }
       const configPath = join(dirs.runtime, "vm.json")