macOS cmsghdr uses socklen_t (4 bytes) for cmsg_len, not size_t
(8 bytes like Linux). The Dart FFI struct was reading at wrong offsets
causing SCM_RIGHTS fd transfer to fail. Added CmsghdrDarwin with
Uint32 cmsg_len alongside the existing Linux layout.
SOL_SOCKET is 0xffff on macOS (was hardcoded to 1 for Linux).
Now platform-detected.
Switched from ad-hoc to Apple Development signing with team ID.
Removed app sandbox from entitlements — proper signing makes it
unnecessary. All SBPL hacks eliminated.
PtySession.spawn() runs recvFd in a child isolate to avoid blocking
the backend isolate's event loop.
Terminal testmode test now passes: pane.spawn via backend isolate
successfully forks and execs the shell.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
