fix: make postinstall spawn-helper chmod work under pnpm GVS

[schickling]

Summary

The current postinstall workaround silently no-ops under pnpm with enableGlobalVirtualStore, leaving node-pty's spawn-helper non-executable and causing posix_spawnp failed at runtime.

Repro

mkdir scratch && cd scratch
pnpm init
pnpm add @myobie/pty
ls -l node_modules/.pnpm/node-pty@*/node_modules/node-pty/prebuilds/darwin-arm64/spawn-helper
# -rw-r--r--  ← should be 755
node -e "import('@myobie/pty/testing').then(m => m.Session.spawn('echo', ['hi']))"
# Error: posix_spawnp failed.

Root cause

The existing postinstall:

"postinstall": "chmod +x node_modules/node-pty/prebuilds/*/spawn-helper 2>/dev/null || true"

uses a relative path that only resolves in flat node_modules layouts. Under pnpm's content-addressed store (especially with enableGlobalVirtualStore), @myobie/pty's lifecycle CWD is ~/Library/pnpm/store/v11/links/@myobie/pty/0.4.1/<hash>/node_modules/@myobie/pty/, and node-pty lives in a sibling content-addressed link — not nested. The relative node_modules/node-pty/... path doesn't exist there. The chmod fails, 2>/dev/null || true swallows the error, and the user is left with a non-executable binary.

The root cause is in node-pty itself (its published tarball ships spawn-helper with mode 0644 and its own post-install never chmods it). The fix is already merged upstream in microsoft/node-pty#858 and #866, but node-pty@1.1.0 (the latest published) predates those merges. So this @myobie/pty workaround needs to actually work until a newer node-pty ships.

The fix

Replace the broken shell chmod with scripts/postinstall.js:

• Uses createRequire(import.meta.url) anchored at this package's own location, then require.resolve('node-pty/package.json') to find node-pty regardless of layout.
• chmod 0755 the platform-specific spawn-helper (Linux + macOS).
• No-op on Windows.
• Silently skips when there's no prebuild for the current arch (acceptable: source builds via node-gyp produce executable binaries directly).
• ESM (matches "type": "module" in package.json).

Also added scripts/ to the published files array — without this, the script doesn't end up in the tarball.

Validation

End-to-end tested locally:

1. npm pack to produce a tarball
2. Installed into a fresh pnpm scratch project with enableGlobalVirtualStore: true
3. Verified find ~/Library/pnpm -name spawn-helper | xargs ls -l shows 0755
4. Verified Session.spawn('echo', ['hi']) works without posix_spawnp failed
5. Confirmed the old shell workaround silently no-ops in the same layout (chmod exits 1, swallowed by || true)

Future

Once a new node-pty release ships with the upstream chmod fix (microsoft/node-pty#858, #866), this scripts/postinstall.js can be deleted entirely — @myobie/pty won't need its own workaround anymore.

Context

I'm building @overeng/pty-effect, an Effect-native wrapper around @myobie/pty, and discovered this while validating against my test suite. Related upstream conversations:

• Expose ./client subpath in package exports map (SessionConnection, spawnDaemon, peekScreen, queryStats, EventFollower) #6 — ./client subpath exports
• EventFollower: ship in package exports + document EventRecord type union #7 — EventFollower shipping

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Filed on behalf of @schickling.