fix(worker): retrieve Soulseek downloads from slskd's dir into staging

SlskdClient enqueued the transfer and polled to Completed but never moved any
files into `dest` — slskd saves them to its OWN downloads dir, so staging stayed
empty and every Soulseek job failed "incomplete download". Qobuz/YouTube write
straight into staging and were unaffected.

- SlskdClient._retrieve() moves the finished files out of slskd's downloads dir
  into staging after completion, matching tolerantly by basename and preferring
  a parent-folder + size match (slskd's on-disk layout varies by version).
- download() returns the moved count as track_count so the pipeline's
  completeness check reflects what actually landed; raises loudly if nothing was
  found (misconfigured/unmounted downloads dir).
- Downloads dir resolves slskd.downloadsDir Config > SLSKD_DOWNLOADS_ROOT env >
  /slskd-downloads default; docker-compose mounts ${SLSKD_DOWNLOADS_DIR} there.
- .env.example documents SLSKD_DOWNLOADS_DIR; retrieval unit-tested offline.

slskd runs as an external daemon, so the shared dir must be a host path both
slskd and the worker mount — set once Lyra runs on the slskd host. Not yet
verified live end-to-end (no slskd access from this VM).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/lyra_worker/adapters/_slskd.py

@@ -1,10 +1,13 @@
 import json
 import os
+import shutil
 import time
 from typing import Callable
 
 import requests
 
+_DEFAULT_DOWNLOADS_ROOT = "/slskd-downloads"
+
 _AUDIO_EXT = {"flac", "mp3", "m4a", "ogg", "opus", "wav", "aac"}
 _LOSSLESS_EXT = {"flac", "wav"}
 _SEARCH_POLLS = 40   # * 3s ≈ 2 min
@@ -34,6 +37,15 @@ class SlskdClient:
     def __init__(self, config: dict):
         self._url = (config.get("slskd.url", "") or "").rstrip("/")
         self._key = config.get("slskd.api_key", "")
+        # Where slskd (an external daemon) writes finished downloads. slskd saves into ITS
+        # OWN directory, so this path must be a share/mount both slskd and this worker see.
+        # Precedence: the slskd.downloadsDir Config row (Settings-overridable) > the
+        # SLSKD_DOWNLOADS_ROOT env (the container mount point) > a sensible default.
+        self._downloads_dir = (
+            config.get("slskd.downloadsDir")
+            or os.environ.get("SLSKD_DOWNLOADS_ROOT")
+            or _DEFAULT_DOWNLOADS_ROOT
+        )
 
     def is_configured(self) -> bool:
         return bool(self._url and self._key)
@@ -138,4 +150,65 @@ class SlskdClient:
 
         if not completed:
             raise TimeoutError(f"soulseek download did not complete for {username}")
-        return {"track_count": total, "path": dest}
+
+        # slskd saved the files into its OWN downloads dir — retrieve them into `dest` so the
+        # pipeline (which verifies + imports against `dest`/staging) actually sees the audio.
+        moved = self._retrieve(files, dest)
+        if moved == 0:
+            raise RuntimeError(
+                f"soulseek transfer completed but no files were found under "
+                f"{self._downloads_dir!r} to move into staging — check that the slskd "
+                f"downloads dir is shared/mounted (SLSKD_DOWNLOADS_ROOT / slskd.downloadsDir)"
+            )
+        return {"track_count": moved, "path": dest}
+
+    def _retrieve(self, files: list[dict], dest: str) -> int:
+        """Move the just-finished slskd files out of its downloads dir into `dest`.
+
+        slskd's on-disk layout can vary by version/config, so match tolerantly: for each
+        wanted file, find on-disk candidates by basename anywhere under the downloads root,
+        then prefer the one whose parent-folder name matches the remote directory and whose
+        size matches. Returns the number of files actually moved. Offline-testable.
+        """
+        root = self._downloads_dir
+        if not root or not os.path.isdir(root):
+            raise RuntimeError(
+                f"slskd downloads dir not found: {root!r} — mount slskd's downloads "
+                f"directory into the worker (SLSKD_DOWNLOADS_ROOT / slskd.downloadsDir)"
+            )
+        os.makedirs(dest, exist_ok=True)
+
+        wanted: dict[str, dict] = {}  # basename(lower) -> {parent, size}
+        for f in files:
+            name = f.get("filename", "")
+            wanted[_basename(name).lower()] = {
+                "parent": _basename(_dirname(name)).lower(),
+                "size": f.get("size"),
+            }
+
+        found: dict[str, list[str]] = {b: [] for b in wanted}
+        for cur_root, _dirs, fnames in os.walk(root):
+            for fn in fnames:
+                key = fn.lower()
+                if key in found:
+                    found[key].append(os.path.join(cur_root, fn))
+
+        moved = 0
+        for basename, paths in found.items():
+            if not paths:
+                continue
+            want = wanted[basename]
+
+            def _score(p: str) -> tuple[int, int]:
+                parent_ok = int(os.path.basename(os.path.dirname(p)).lower() == want["parent"])
+                size_ok = 0
+                try:
+                    size_ok = int(bool(want["size"]) and os.path.getsize(p) == want["size"])
+                except OSError:
+                    pass
+                return (parent_ok, size_ok)
+
+            best = max(paths, key=_score)
+            shutil.move(best, os.path.join(dest, os.path.basename(best)))
+            moved += 1
+        return moved