Function compact 

pub fn compact(
    messages: &[Message],
    strategy: &dyn CompactionStrategy,
    tokenizer: &dyn Tokenizer,
) -> Vec<Message>

Compact messages with strategy and tokenizer.

This is the supported entry point: it runs the strategy and then enforces the retention and pairing invariants (finalize_compaction). Calling CompactionStrategy::compact directly gives the strategy’s raw output without them.