Complete the Linux-aligned seat-takeover primitive set: a raw consumer can take
an EXCLUSIVE grab of the input stream by writing a single control byte to its
own consumer_raw handle (1=grab, 0=ungrab) — self-identifying, unlike the
shared control fd. While a grab is held:
* events route ONLY to the grabbing handle;
* the text console AND every other raw tap are suspended; and
* the grab is released automatically when the handle closes, so a compositor
that crashes cannot wedge input away from the console (Linux
__input_release_device).
A second grab attempt by a different handle returns EBUSY. Additive and
behaviour-preserving: grab defaults to None, so nothing changes until a client
grabs. new_raw() now opens read+write and ConsumerHandle::set_grab() drives it.
Together with set_vt_mode (KDSKBMODE) this gives seatd/a compositor the full
grab + VT-mode takeover surface. Compile-checked for x86_64-unknown-redox;
boot-validation pending build-green.
Red Bear OS
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