flush

Emit anything still buffered and end the journey.

An algorithm that looks at a window of fixes — a median filter, a stop detector, a map-matcher — has pending output when the last fix arrives, and no way to know it was the last. Without this, the tail of every trip is silently dropped. Online algorithms that buffer nothing correctly return an empty list, which is why this has a default.

Added after a cross-model design review flagged the missing terminator as the most likely source of a quiet, systematic under-count.