Trait ContextWatcher 

pub trait ContextWatcher: Send + Sync {
    // Provided methods
    fn on_inject(&self, msg: &dyn Debug, pos: Position) -> WatcherVerdict { ... }
    fn on_remove(&self, count: usize) -> WatcherVerdict { ... }
    fn on_pre_compact(&self, message_count: usize) -> WatcherVerdict { ... }
    fn on_post_compact(&self, removed: usize, remaining: usize) { ... }
}

Observer and gatekeeper for mutations to an OperatorContext.

All methods have default implementations that approve the operation (Allow or no-op). Implementors override only the methods they care about.

Watchers are stored as Arc<dyn ContextWatcher> and must be Send + Sync. Long-running or I/O-heavy watcher logic will add latency to every mutation; keep implementations fast.

Object safety

The trait is object-safe. on_inject receives the message as a type-erased fmt::Debug reference (the concrete ContextMessage<M>) so implementations can inspect its debug representation without requiring a generic method.

Provided Methods

fn on_inject(&self, msg: &dyn Debug, pos: Position) -> WatcherVerdict

Called before a message is injected.

msg is the full ContextMessage<M> coerced to &dyn fmt::Debug. pos is the requested injection position.

Return WatcherVerdict::Reject to abort the inject.

fn on_remove(&self, count: usize) -> WatcherVerdict

Called before messages are removed (truncate or filter operations).

count is the number of messages about to be removed. Return WatcherVerdict::Reject to abort the removal.

fn on_pre_compact(&self, message_count: usize) -> WatcherVerdict

Called before a OperatorContext::replace_messages compaction runs.

message_count is the number of messages currently in the context. Return WatcherVerdict::Reject to abort the compaction.

fn on_post_compact(&self, removed: usize, remaining: usize)

Called after a OperatorContext::replace_messages compaction completes.

removed is the number of messages dropped (old_count - new_count, clamped to 0). remaining is the count of messages now in the context.

Implementors