Bugfix: don't mark successes as failures by accident

projects/tentacles/src/python/tentacles/schema.sql

@@ -576,6 +576,7 @@ SET
  , message = :message
 WHERE
    id = :jid
+   AND finished_at IS NULL -- guard against calling this twice
 ;
 
 -- name: delete-job!

projects/tentacles/src/python/tentacles/workers.py

@@ -230,7 +230,7 @@ def pull_jobs(app: App, db: Db) -> None:
                 log.info(f"Job {job.id} has been acknowledged as cancelled")
                 db.finish_job(jid=job.id, state="cancelled")
 
-            if printer_state.get("printing"):
+            elif printer_state.get("printing"):
                 pass
 
             else: