- Run the trainer's caption discovery in the start route BEFORE freeing GPU
residents, so a missing or uncaptionable dataset 400s without evicting the
loaded chat/Images model.
- sd.cpp unload now waits out a cancelled one-shot generation on the generate
lock before reporting the device free, matching the diffusers backend.
- Clearing a caption that came from metadata.jsonl writes an empty sidecar
tombstone instead of unlinking (both readers treat an existing sidecar as
authoritative), so the cleared label cannot resurface.
- The ControlNet wrapper pipe is only cached while its load is still current,
closing the unload race the model cache already handled.
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