Function select_compaction_strategy 

pub fn select_compaction_strategy(
    capabilities: &CompactionCapabilities<'_>,
) -> CompactionStrategy

Select the preferred compaction strategy for a provider/model pair.

For now this always falls back to Local unless provider-native compaction is explicitly allowed and the provider matches a known future optimization seam. This keeps the local/manual contract canonical while avoiding TUI- or provider-specific branching throughout the rest of the codebase.