62e7651fe7
endpoint::serve used register_sync_scheme, which registers the scheme to
the daemon's own namespace but never returns the capability fd to init.
For type={scheme} services init blocks in call_ro(FD) waiting for that
fd, so the boot deadlocked right after 'Started Intel LPSS I2C
controller' (CPU halted, init asleep) — the ptyd-class bug.
Replace register_sync_scheme with an explicit capability-fd creation +
notify_init_scheme_fd() that writes the fd to the INIT_NOTIFY pipe
(same mechanism as SchemeDaemon::ready_with_fd / ready_sync_scheme,
which i2cd, ucsid, and ptyd already use). init then registers
/scheme/<name> and the boot proceeds.
Affects intel-lpss-i2cd and dw-acpi-i2cd, both type={scheme} services
using this endpoint.