Summary

On macOS, pnpm exec tsx examples/quickstart/src/simple.ts can fail during V8 runtime bootstrap if the default TMPDIR is long enough to push the Unix socket path past Darwin's sun_path limit.

The same command succeeds with a shorter TMPDIR, so this is not a tsx issue. The Rust V8 runtime is binding its socket under std::env::temp_dir() with a path shape that is too long for some macOS temp roots.

Minimal repro

Fails with default macOS temp dir:

pnpm exec tsx examples/quickstart/src/simple.ts

Observed:

Error: V8 runtime process closed stdout before sending socket path

Works with short temp dir:

TMPDIR=/tmp/se pnpm exec tsx examples/quickstart/src/simple.ts

Observed:

hello from secure-exec

Direct control against the packaged runtime shows the real failure:

failed to bind UDS: path must be shorter than SUN_LEN

Impact

• breaks the documented quickstart flow on some macOS setups
• surfaces a misleading bootstrap error instead of the real bind failure
• likely affects any macOS V8-runtime startup path using a long default TMPDIR

Root cause

native/v8-runtime/src/main.rs creates a socket path like:

<temp_dir>/secure-exec-<32 hex>/secure-exec.sock

On macOS, default temp roots like /var/folders/.../T/ are already long. After appending the secure-exec-specific directory and socket name, UnixListener::bind() can exceed Darwin's UDS path limit and fail before the runtime prints its socket path to stdout.

packages/v8/src/runtime.ts then reports the generic stdout-close error instead of surfacing stderr.