0.6.9: Finish the Stage 4 path revisit in the three remaining scripts

The 2026-07-08 path rewrite changed beets' displayed paths from the
transitional /music/... mount to real /data/music/Library/... paths.
dedup-library.sh was fixed in 0.6.8; three more scripts still assumed
the old prefix, each failing silently:

- replace-with-better.sh resolved every library match to a doubled
  nonexistent path, logged [stale-db], skipped the in-place replace,
  and then imported the staged FLAC as a NEW track via the
  leftover-import step. Net effect: the mp3-to-flac upgrade flow
  produced flac+mp3 twin pairs in the library (surfacing in the dedup
  queue) instead of replacing the MP3 in place.

- fix-track-metadata.py queried beets only by the legacy /music/...
  form, matched nothing, and silently skipped beet update/move after
  retagging.

- export-laptop-playlists.py filtered out every library track (no
  displayed path starts with /music/ anymore), producing empty
  exports.

All three now use the real displayed path and keep the /music/... form
only as a legacy fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pipeline/lib/replace-with-better.sh

@@ -195,7 +195,18 @@ while IFS= read -r -d '' new_file; do
   existing_id="${match%%$'\x1f'*}"
   existing_container="${match#*$'\x1f'}"
 
-  existing="${MUSIC_DATA_DIR:-/data/music}/Library${existing_container#/music}"
+  # beets displays real ${MUSIC_DATA_DIR}/Library/... paths since the
+  # 2026-07-08 path rewrite -- use them as-is; only a legacy /music/...
+  # display path still needs the prefix swap. Blindly prepending (the old
+  # behavior) doubled the prefix, so every match logged [stale-db], the MP3
+  # never got replaced, and the leftover-import step at the bottom imported
+  # the staged FLAC as a NEW track -- producing exactly the flac+mp3 twins
+  # this script exists to prevent.
+  if [[ "$existing_container" == /music/* ]]; then
+    existing="${MUSIC_DATA_DIR:-/data/music}/Library${existing_container#/music}"
+  else
+    existing="$existing_container"
+  fi
   if [[ ! -f "$existing" ]]; then
     echo "[stale-db]       beets has $existing_container but file missing" | tee -a "$LOG"
     continue