Release v19.50.1

Fixed

• An observer no longer skips events when the storage lookup for its next relevant event fails. It keeps its position, stays in routing without delivering anything, and retries on the next watchdog pass instead of fast-forwarding to the tail. (#4770)
• The observer documentation now matches the current behavior: projection replay and catch-up run as one ordered step, [OnceOnly] excludes replays rather than limiting a handler to one run per event source, and the quarantine and replay descriptions in the observers concept page are corrected. (part of #4748)