Make the artist a gate, not a quarter of the score

Requesting "Michael Jackson - Chicago" filed The Fall's "Chicago, Now!" from
Extricate. The chain: the artist name is filtered by the Soulseek server, so
the ladder correctly fell back to the bare title -- at which point the result
set is every song anyone has ever called Chicago, and the artist is the only
thing telling them apart.

match_ratio weights the artist at 0.25, so a perfect title with no artist
anywhere scores 0.75. That clears MIN_MATCH, and the ~22 point gap it leaves
against a genuine match is nothing next to the 340 points score() awards for a
free upload slot and a short queue. An idle peer holding the wrong song
therefore beat a busy peer holding the right one, every time.

That is the failure the confidence score was explicitly designed to prevent --
"a fast peer must not be able to raise the confidence of a wrong match" -- and
rewriting score() to rank availability first reintroduced it on the other side
of the wall. Availability is a tiebreak among plausible files; it is never a
reason to take a different song.

Candidates whose path names the artist are now kept outright and the rest
discarded, falling back to title-only matches only when there are none. The
downstream confidence gate still ran correctly here: it scored 0.75, said
"artist not found in path", and held the file for review.

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

tests/test_acquisition.py

@@ -161,6 +161,35 @@ def main() -> int:
     check("reordered filename still matches",
           app.match_ratio(r"x\Creep - Radiohead.mp3", "Radiohead", "Creep") == 1.0)
 
+    print("\nthe artist gate")
+    check("artist named in the folder is confirmed",
+          app.artist_confirmed(r"m\Michael Jackson\Xscape\02 Chicago.flac",
+                               "Michael Jackson"))
+    check("a different band's song with the same title is not",
+          not app.artist_confirmed(
+              r"@@jwbvv\Music\The Fall\1990-Extricate\08-Chicago, Now!.flac",
+              "Michael Jackson"))
+    check("out-of-order naming still counts",
+          app.artist_confirmed(r"x\Jackson, Michael - Chicago.flac",
+                               "Michael Jackson"))
+
+    # The real regression: bare-title search returns every song called
+    # "Chicago", and an available stranger used to outrank a queued match.
+    gate = FakeSlskd(per_query={"Chicago": [
+        peer("stranger", r"@@x\Music\The Fall\1990-Extricate\08-Chicago, Now!.flac",
+             slot=True, queue=0),
+        peer("correct", r"m\Michael Jackson\XSCAPE\02 - Chicago.flac",
+             slot=False, queue=300),
+    ]})
+    app.slskd_client = gate
+    make_job("j6", "Michael Jackson", "Chicago")
+    asyncio.run(app.pick_and_enqueue("j6", "Michael Jackson", "Chicago"))
+    r = job_row("j6")
+    check("the right artist wins even from a peer with 300 queued",
+          r["username"] == "correct", f"picked {r['username']}")
+    check("and the wrong-artist file is dropped, not merely ranked lower",
+          len(json.loads(r["candidates"] or "[]")) == 0, r["candidates"])
+
     print("\ncandidate ladder")
     fake = FakeSlskd(per_query={
         "Billie Jean": [peer("alice", r"m\Michael Jackson\Billie Jean.flac"),