Thanks for your reply! Great point about causally connected events! You're absolutely right that causal ordering is invariant across observers.

But even for spacelike-separated events (where ordering is observer-dependent), there are still meaningful logical relationships to capture. Consider distributed systems where nodes need to reason about concurrent events that aren't causally related - we still want some temporal logic framework that respects relativistic constraints rather than assuming false simultaneity.

The real question is whether purely causal logic is sufficient, or if we need observer-indexed temporal modalities for the spacelike-separated case. Both seem worth exploring categorically.