Enum Overflow 

pub enum Overflow {
    Block,
    DropNewest,
}

溢出策略：有界队列满时怎么办（每实例固定一种）。

Variants

Block

队满 send().await 阻塞泵 → 背压传导回 tick_tx（慢而不丢）。Persist / Http(必达) 用。

DropNewest

队满 try_send 失败即丢**当前（最新）**条目（warn，泵不阻塞）。HttpFire 用（丢失靠 cursor-gate 重发自愈）。

语义：try_send 满时丢的是本次（新来的）请求，不是队列里最旧的那条。 在 fire-and-forget 自愈场景下等价（两端都靠 cursor-gate 重发补），取最简实现（try_send-Full-drop）。

Trait Implementations

impl Clone for Overflow

fn clone(&self) -> Overflow

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Overflow

impl Debug for Overflow

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

Formats the value using the given formatter.

impl Eq for Overflow

impl PartialEq for Overflow

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Overflow