Prune stems whose source song was removed or replaced

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -123,6 +123,9 @@ To update, copy the new files, rebuild, `docker rm -f` the container and run it
 | `MODEL` | `roformer_bs_sw` | Any id from [the model table](#separation-models) |
 | `DEVICE` | `cuda` | `cuda`, `cuda:N` or `cpu` |
 | `RESCAN_MIN` | `30` | Minutes between library scans once caught up |
+| `PRUNE` | `1` | Remove stems whose song is gone from the library, at start and every `RESCAN_MIN` |
+| `PRUNE_CHANGED` | `0` | Also remove stems of songs replaced in place (size or mtime changed) |
+| `PRUNE_MAX` | `0.2` | Skip a prune that would remove more than this share of the stems. `server/prune.py` is the manual dry run, `--apply` to remove |
 | `AUTO_SCAN` | `0` | `1` to scan the library on a timer. Off by default: only Stem Now requests are separated |
 | `FP16` | `1` | Half precision on the GPU (`0` for fp32) |
 | `OVERLAP`, `SEGMENT`, `SHIFTS` | `0.25`, `0`, `0` | Separation quality, same as the desktop app |