feat(notifications): library health reaches admins, coalesced (#5341)

- A failed scan run sends scan_failed. Each failure adds to the count and
  the notice shows the latest error. A scan cut short by shutdown says
  nothing.
- Marking tracks missing sends tracks_missing with a running count.
- A duplicate sweep that proposes a group it had not proposed before
  sends duplicates_found, counting everything awaiting review. A sweep
  that only re-finds known groups stays quiet, so a read notice isn't
  repeated every sweep (CountDuplicateGroupsDetectedSince).
- A playback-error report sends playback_errors, counting the unresolved
  errors (CountUnresolvedPlaybackErrors).

The library package gets its notifier as a package-level SetNotifier
beside SetEventBus, for the same reason the bus is package-level.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/notify_test.go

@@ -0,0 +1,180 @@
+package library
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"path/filepath"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/dbtest"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/notifications"
+)
+
+// notifyingAdmin wires a real notifier for the test and returns an admin whose
+// inbox the test reads.
+func notifyingAdmin(t *testing.T, pool *pgxpool.Pool) dbq.User {
+	t.Helper()
+	admin, err := dbq.New(pool).CreateUser(context.Background(), dbq.CreateUserParams{
+		Username: dbtest.TestUserPrefix + "libnotify", PasswordHash: "x", ApiTokenHash: "x", IsAdmin: true,
+	})
+	if err != nil {
+		t.Fatalf("admin: %v", err)
+	}
+	SetNotifier(notifications.New(pool, nil, nil))
+	t.Cleanup(func() { SetNotifier(nil) })
+	return admin
+}
+
+type notice struct {
+	kind  string
+	count int64
+	body  string
+}
+
+func unreadNotices(t *testing.T, pool *pgxpool.Pool, user dbq.User) []notice {
+	t.Helper()
+	rows, err := dbq.New(pool).ListNotifications(context.Background(), dbq.ListNotificationsParams{
+		UserID: user.ID, PageLimit: 50,
+	})
+	if err != nil {
+		t.Fatalf("list notifications: %v", err)
+	}
+	var out []notice
+	for _, r := range rows {
+		if r.ReadAt.Valid {
+			continue
+		}
+		var p notifications.Payload
+		if err := json.Unmarshal(r.Payload, &p); err != nil {
+			t.Fatalf("payload: %v", err)
+		}
+		out = append(out, notice{kind: r.Kind, count: p.Count, body: p.Detail})
+	}
+	return out
+}
+
+func TestNotifyScanFinished_FailuresCoalesceAndShutdownIsSilent(t *testing.T) {
+	pool := newPool(t)
+	admin := notifyingAdmin(t, pool)
+	ctx := context.Background()
+
+	notifyScanFinished(ctx, "")
+	if got := unreadNotices(t, pool, admin); len(got) != 0 {
+		t.Fatalf("a clean scan notified: %+v", got)
+	}
+
+	cancelled, cancel := context.WithCancel(ctx)
+	cancel()
+	notifyScanFinished(cancelled, "library: context canceled")
+	if got := unreadNotices(t, pool, admin); len(got) != 0 {
+		t.Fatalf("a scan cut short by shutdown notified: %+v", got)
+	}
+
+	notifyScanFinished(ctx, "library: root /music missing")
+	notifyScanFinished(ctx, "library: root /music still missing")
+	got := unreadNotices(t, pool, admin)
+	if len(got) != 1 || got[0].kind != string(notifications.KindScanFailed) || got[0].count != 2 ||
+		got[0].body != "library: root /music still missing" {
+		t.Fatalf("notices = %+v, want one scan_failed counting 2 with the latest error", got)
+	}
+}
+
+func TestReconcileMissing_NotifiesAdminsWithARunningCount(t *testing.T) {
+	pool := newPool(t)
+	admin := notifyingAdmin(t, pool)
+	s := testScanner(t, populatedRoot(t))
+
+	// Two scans, each losing 2 of 10 tracks (under the mark cap).
+	for pass := 0; pass < 2; pass++ {
+		rows := make([]dbq.ListTrackPathsForReconcileRow, 0, 10)
+		seen := map[string]struct{}{}
+		for i := 0; i < 10; i++ {
+			p := fmt.Sprintf("/music/pass-%d-%02d.mp3", pass, i)
+			rows = append(rows, row(byte(pass*10+i), p, false))
+			if i >= 2 {
+				seen[p] = struct{}{}
+			}
+		}
+		var stats Stats
+		if err := s.reconcileMissing(context.Background(), &fakeReconciler{rows: rows}, seen, &stats); err != nil {
+			t.Fatalf("reconcile pass %d: %v", pass, err)
+		}
+	}
+
+	got := unreadNotices(t, pool, admin)
+	if len(got) != 1 || got[0].kind != string(notifications.KindTracksMissing) || got[0].count != 4 {
+		t.Fatalf("notices = %+v, want one tracks_missing counting 4", got)
+	}
+}
+
+func TestDuplicateSweep_NotifiesOnlyWhenSomethingNewIsProposed(t *testing.T) {
+	pool := newPool(t)
+	admin := notifyingAdmin(t, pool)
+	ctx := context.Background()
+	q := dbq.New(pool)
+	dir := t.TempDir()
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+
+	_, album, artist := seedTrack(t, pool, filepath.Join(dir, "seed.mp3"))
+	// Same audio-stream hash: an exact pair, whatever the prints say.
+	pair := func(name string, b byte, seed uint64) {
+		t.Helper()
+		for i := 1; i <= 2; i++ {
+			tr, err := q.UpsertTrack(ctx, dbq.UpsertTrackParams{
+				Title: name, AlbumID: album.ID, ArtistID: artist.ID, DurationMs: 200000,
+				FilePath: filepath.Join(dir, fmt.Sprintf("%s-%d.mp3", name, i)), FileSize: 100, FileFormat: "mp3",
+			})
+			if err != nil {
+				t.Fatalf("track %s: %v", name, err)
+			}
+			if err := q.UpsertTrackFingerprint(ctx, dbq.UpsertTrackFingerprintParams{
+				TrackID: tr.ID, AudioStreamSha256: bytes.Repeat([]byte{b}, 32),
+				Chromaprint: randomPrint(seed+uint64(i), printLen), FingerprintVersion: fingerprintVersion,
+				ChromaprintLengthSec: defaultChromaprintLengthSec,
+			}); err != nil {
+				t.Fatalf("fingerprint %s: %v", name, err)
+			}
+		}
+	}
+	sweep := func() {
+		t.Helper()
+		if _, err := runDuplicateSweep(ctx, pool, logger, DefaultFingerprintSettings, duplicateCandidatePage); err != nil {
+			t.Fatalf("sweep: %v", err)
+		}
+	}
+	markAllRead := func() {
+		t.Helper()
+		if _, err := q.MarkAllNotificationsRead(ctx, admin.ID); err != nil {
+			t.Fatalf("mark read: %v", err)
+		}
+	}
+
+	pair("first", 1, 100)
+	sweep()
+	got := unreadNotices(t, pool, admin)
+	if len(got) != 1 || got[0].kind != string(notifications.KindDuplicatesFound) || got[0].count != 1 {
+		t.Fatalf("after the first sweep notices = %+v, want one duplicates_found counting 1", got)
+	}
+
+	// Read, then swept again with nothing new: no reminder.
+	markAllRead()
+	sweep()
+	if got := unreadNotices(t, pool, admin); len(got) != 0 {
+		t.Fatalf("a sweep that found nothing new notified: %+v", got)
+	}
+
+	// A new pair is news, and the count is everything awaiting review.
+	pair("second", 2, 200)
+	sweep()
+	got = unreadNotices(t, pool, admin)
+	if len(got) != 1 || got[0].count != 2 {
+		t.Fatalf("after a new pair notices = %+v, want one counting 2", got)
+	}
+}