Porting to a new architecture

To write

What a new arch must provide under arch/. aarch64, RISC-V and x86 are the targets.

The HAL contract

• arch headers, make hal-check, asm-offsets

Traps and the syscall ABI

• ArchInvokeSvc*, frame layout, trap_frame = kstack_top − sizeof(CpuState)

Timer and counter

• one-shot deadline, user-readable counter