Fewer SD card writes while offline: Signal K AIS plugin 0.4.0

The offline queue writes far less to the SD card. Each queue file used to be rewritten from scratch every fifteen seconds as sentences were added to it, so a boat at anchor hearing a slow trickle of traffic wrote the same data to the card a dozen times over. Sentences are now appended to the end of a file and nothing is rewritten, which on a quiet anchorage cuts the writing to a fraction of what it was.
A replay the server only partly accepts no longer rewrites anything on disk, and a queue file damaged by a power cut costs one sentence instead of the five hundred it was sharing a file with.
The queue keeps working when the plugin cannot delete a file, as happens when an SD card turns read-only. A queue file that could neither be read nor removed used to stop the replay where it stood until the next reconnect, and files the server had already taken could be left behind in a way that made the 100 MB cap discard data that had not been sent yet. Files that will not delete are now set aside, retried in the background, and never replayed.