QMediaPlayer.setSource() no-ops on an unchanged URL, so replaying the
track that was already the loaded source never re-fired LoadedMedia and
the armed _pending_start_ms was silently dropped — a freshly edited
start time appeared to save but playback began at 0:00. _load_current
now detects the unchanged source and stop()+seeks directly (a forced
clear+reload was tried and races the FFmpeg backend, snapping the seek
back to 0). previous()-restart likewise rewinds to the custom start
time instead of 0:00.
Verified live via an offscreen GUI harness: replay-while-playing,
replay-after-EndOfMedia, and cleared-start-time replay.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
