feat(api): add GET /api/artists/{id}/tracks handler

Wires ListArtistTracksForUser (Task 3 SQL) to a new handler that returns
all quarantine-filtered tracks for an artist as a flat TrackRef list.
404 when the artist doesn't exist. Route registered in Mount().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/library_test.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"encoding/json"
 	"io"
 	"log/slog"
@@ -12,6 +13,7 @@ import (
 	"github.com/go-chi/chi/v5"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/config"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playevents"
 )
 
@@ -465,3 +467,103 @@ func TestRoutesRegisteredInMount(t *testing.T) {
 		}
 	}
 }
+
+func TestGetArtistTracks_HappyPath(t *testing.T) {
+	h, pool := testHandlers(t)
+	user := seedUser(t, pool, "alice", "pw", false)
+	q := dbq.New(pool)
+	artist, _ := q.UpsertArtist(context.Background(), dbq.UpsertArtistParams{
+		Name: "ArtistA", SortName: "ArtistA",
+	})
+	album, _ := q.UpsertAlbum(context.Background(), dbq.UpsertAlbumParams{
+		Title: "AlbumA", SortTitle: "AlbumA", ArtistID: artist.ID,
+	})
+	_, _ = q.UpsertTrack(context.Background(), dbq.UpsertTrackParams{
+		Title: "T1", AlbumID: album.ID, ArtistID: artist.ID,
+		DurationMs: 1000, FilePath: "/tmp/m6a-T1.mp3",
+		FileSize: 1, FileFormat: "mp3",
+	})
+	_, _ = q.UpsertTrack(context.Background(), dbq.UpsertTrackParams{
+		Title: "T2", AlbumID: album.ID, ArtistID: artist.ID,
+		DurationMs: 1000, FilePath: "/tmp/m6a-T2.mp3",
+		FileSize: 1, FileFormat: "mp3",
+	})
+
+	r := chi.NewRouter()
+	r.Get("/api/artists/{id}/tracks", h.handleGetArtistTracks)
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/"+uuidToString(artist.ID)+"/tracks", nil)
+	req = withUser(req, user)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, body = %s", w.Code, w.Body.String())
+	}
+	var got []TrackRef
+	if err := json.Unmarshal(w.Body.Bytes(), &got); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if len(got) != 2 {
+		t.Fatalf("len = %d, want 2", len(got))
+	}
+	if got[0].ArtistName != "ArtistA" || got[0].AlbumTitle != "AlbumA" {
+		t.Errorf("got = %+v", got[0])
+	}
+}
+
+func TestGetArtistTracks_HonorsQuarantine(t *testing.T) {
+	h, pool := testHandlers(t)
+	user := seedUser(t, pool, "alice", "pw", false)
+	q := dbq.New(pool)
+	artist, _ := q.UpsertArtist(context.Background(), dbq.UpsertArtistParams{
+		Name: "ArtistB", SortName: "ArtistB",
+	})
+	album, _ := q.UpsertAlbum(context.Background(), dbq.UpsertAlbumParams{
+		Title: "AlbumB", SortTitle: "AlbumB", ArtistID: artist.ID,
+	})
+	track, _ := q.UpsertTrack(context.Background(), dbq.UpsertTrackParams{
+		Title: "Q", AlbumID: album.ID, ArtistID: artist.ID,
+		DurationMs: 1000, FilePath: "/tmp/m6a-Q.mp3",
+		FileSize: 1, FileFormat: "mp3",
+	})
+	if _, err := pool.Exec(context.Background(),
+		`INSERT INTO lidarr_quarantine (user_id, track_id, reason) VALUES ($1, $2, 'bad_rip')`,
+		user.ID, track.ID,
+	); err != nil {
+		t.Fatalf("quarantine insert: %v", err)
+	}
+
+	r := chi.NewRouter()
+	r.Get("/api/artists/{id}/tracks", h.handleGetArtistTracks)
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/"+uuidToString(artist.ID)+"/tracks", nil)
+	req = withUser(req, user)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d", w.Code)
+	}
+	var got []TrackRef
+	_ = json.Unmarshal(w.Body.Bytes(), &got)
+	if len(got) != 0 {
+		t.Errorf("len = %d, want 0 (quarantined)", len(got))
+	}
+}
+
+func TestGetArtistTracks_NotFound(t *testing.T) {
+	h, pool := testHandlers(t)
+	user := seedUser(t, pool, "alice", "pw", false)
+
+	r := chi.NewRouter()
+	r.Get("/api/artists/{id}/tracks", h.handleGetArtistTracks)
+	// Random UUID — no such artist exists.
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/00000000-0000-0000-0000-000000000000/tracks", nil)
+	req = withUser(req, user)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want 404", w.Code)
+	}
+	_ = pool
+}