Bug: Configured library folder (`dlc_dir`) is not scanned by Rescan/Full Rescan

[nullohm]

Bug: Configured library folder (dlc_dir) is not scanned by Rescan/Full Rescan

Summary

After changing the "Library folder path" in Settings (and confirming the new
path exists and contains valid .feedpak files), neither Rescan Library
nor Full Rescan picks up songs from that folder. The songs table in
web_library.db only ever contains the bundled starter/diagnostic content —
external songs never get indexed, regardless of the configured path.

Steps to reproduce

1. Have a working library with externally-converted .feedpak files that
   were previously scanned successfully.
2. Move/rename the folder containing those files (e.g. into a subfolder).
3. Update "Library folder path" in Settings to the new location and click
   Save.
4. Click Rescan Library, then Full Rescan.
5. Song Library still only shows the built-in starter songs; external songs
   never appear, "Unmatched" is empty.

Evidence

• config.json correctly contains the updated path:

  "dlc_dir": "/home/<user>/Documents/feedback/"

• However, scan_dir_signature.json (which appears to record what was
  actually scanned) points to the bundled library instead:

  {"dlc": "/home/<user>/.local/share/feedback/library", "dirs": {...}}

• Querying web_library.db directly confirms only bundled content is
  indexed:

  sqlite3 ~/.config/feedback-desktop/slopsmith-config/web_library.db "SELECT filename FROM songs;"
  

  → only returns starter/... and diagnostics-builtin/... entries, no
  external songs.
• ~/.config/feedback-desktop/slopsmith-config/sloppak_cache/ contains
  per-song subfolders for the external songs from an earlier successful
  scan (before the folder was moved), confirming external scanning worked
  previously and that the regression is tied to the path change / rescan
  not re-targeting dlc_dir.

Expected behavior

Rescan/Full Rescan should scan the path currently configured in
dlc_dir (Settings → Library folder path), not a stale/cached location.

Environment

• OS: openSUSE Tumbleweed (Linux)
• feedBack desktop (Electron-based build)
• Install method: AppImage

Workaround attempted

• Verified path is correct and exists (confirmed via file manager).
• Restarted app, killed background process (pkill -f feedback-desktop)
  before retrying — no change.
• Full Rescan (which per its own description "clears the cache and
  re-imports everything") did not resolve the issue.

[nullohm]

Workaround found

Managed to fix this without a rescan by editing
scan_dir_signature.json directly (instead of config.json, which
turned out to be irrelevant to the actual scan behavior):

~/.config/feedback-desktop/slopsmith-config/scan_dir_signature.json

This file seems to be the actual source of truth for what the scanner
considers "already indexed" — not dlc_dir in config.json. Steps:

1. Fully quit the app (pkill -f feedback-desktop on Linux — background
   process survives closing the window).
2. Back up the file, then replace its contents with:

   {"dlc": "/path/to/actual/library/folder/", "dirs": {}}

   (empty "dirs" object — this is what forces the scanner to treat
   everything under the path as unindexed.)
3. Restart the app.

Songs from the new path showed up immediately on next launch — no manual
Rescan/Full Rescan needed.

This strongly suggests the scanner reads its target path from
scan_dir_signature.json rather than from the dlc_dir value in
config.json/Settings, and that Settings → Save doesn't update
scan_dir_signature.json accordingly — which is likely the actual root
cause of the bug described above.