`drain`

void drain(PhaseIndex phase) noexcept

Parameters

Name	Type
`phase`	`PhaseIndex`

Delivers every event phase has not seen, channel by channel.

Precondition

The caller is the main thread and no dispatch (a drain or a publish_immediate call) is already in progress.

Merges every lane once at entry, then again before a later channel only if lanes_dirty_ shows a handler published since, never unconditionally.