Enum OverflowPolicy 

#[repr(u8)]
pub enum OverflowPolicy {
    Reject = 0,
    DropNewest = 1,
    DropOldest = 2,
}

What happens when a hop would exceed the mailbox’s logical capacity.

Why there is no Block

Parking the OS worker on a full mailbox would stall every other flow on that thread — the opposite of an M:N scheduler. Backpressure that waits belongs to a future scheduler state (WAITING_SEND → runnable when a slot frees), not to a queue method that holds a worker.

This revision therefore only offers non-blocking overflow:

Policy	Effect
Reject	Hop is not accepted; caller sees super::MailboxFull / crate::SendError::MailboxFull
DropNewest	Incoming hop discarded; queue unchanged
DropOldest	Oldest queued hop dropped, incoming enqueued (still FIFO among survivors)

Default is Reject: fail-closed. Silent drop is an explicit embedder choice.

Variants

Reject = 0

DropNewest = 1

DropOldest = 2

Trait Implementations

impl Clone for OverflowPolicy

fn clone(&self) -> OverflowPolicy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for OverflowPolicy

impl Debug for OverflowPolicy

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for OverflowPolicy

fn default() -> Self

Returns the “default value” for a type.

impl Eq for OverflowPolicy

impl PartialEq for OverflowPolicy

fn eq(&self, other: &OverflowPolicy) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for OverflowPolicy