Function prepare_context_switch 

pub unsafe fn prepare_context_switch<'switch>(
    pin: &'switch CpuPin<'_>,
    previous: Pin<&ExecutionContextHeader>,
    next: Pin<&ExecutionContextHeader>,
) -> Result<(PreparedContextSwitch<'switch>, PreviousContextBinding), ContextSwitchError>

Validates and binds a complete execution-context switch transaction.

All fallible validation occurs before the returned prepared token can be committed. Dropping the prepared token automatically rolls back next.

Safety

The caller must own the IRQ-disabled context-switch path. Both headers must remain pinned and alive through the raw switch and incoming tail.