feat: a wanted list — follow artists on release-type profiles; requests and re-acquisition become wants (M502 #5520)

Minstrel keeps its own list of what it is to get, keyed by MusicBrainz
release group. A want comes from an approved request, a new release by a
followed artist, or an album whose files went missing, and is held once the
library has a full edition of it.

- Migration 0081: release_type_profiles (Standard seeded: Album, EP,
  Single, studio only), follows, follow_seen_groups and wants.
  lidarr_requests becomes requests with plain *_mbid columns; approved
  album and track requests move onto the wanted list, approved artist
  requests become follows, and the library's album artists start out
  followed. missing_reacquisitions and the retry settings go.
- internal/wanted: follows are checked against MusicBrainz discographies
  daily. The first check sets a baseline, and only releases after it are
  wanted unless the follow asked for what already exists. Profiles filter
  by primary and secondary type, so live recordings stay out unless a
  profile ticks Live.
- internal/requests (was lidarrrequests): approving puts the request on
  the wanted list, and an artist request can be approved on a chosen
  profile. A request completes when its want is held.
- The re-acquisition sweeper wants a missing album back instead of asking
  Lidarr; searching for it is the search schedule's (#5521).
- Web: an admin Wanted page (Wanted, Missing files, Held, Following), a
  follow control on artist pages, a release-type profiles card on
  Integrations, "Approve on a profile" on Requests, and want state on
  Missing files. The artist detail API returns the artist's MBID.
- Android: the request body sends artist_mbid, album_mbid and track_mbid.

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

internal/reacquisition/settings.go

@@ -1,11 +1,12 @@
-// Package reacquisition turns a missing file back into a Lidarr request
-// without anyone pressing anything (milestone #290).
+// Package reacquisition wants an album back when its files go missing,
+// without anyone pressing anything (milestone #290; a want rather than a
+// Lidarr request since M502 #5520).
 //
-// The unit of work is the ALBUM, not the track. Lidarr acquires releases;
-// there is no meaningful "fetch me one track", and a track-kind request needs
-// a recording MBID plenty of files lack. Grouping also does most of the
+// The unit of work is the ALBUM, not the track. Music is acquired as
+// releases; there is no meaningful "fetch me one track", and a recording
+// MBID is something plenty of files lack. Grouping also does most of the
 // safety work: the loss that produced #2523 — three reorganised albums, ~40
-// missing files — becomes three requests rather than forty.
+// missing files — becomes three wants rather than forty.
 package reacquisition
 
 import (
@@ -14,7 +15,6 @@ import (
 	"fmt"
 	"log/slog"
 	"sync"
-	"time"
 
 	"github.com/jackc/pgx/v5/pgxpool"
 
@@ -24,13 +24,9 @@ import (
 // Settings is the operator-tunable policy, mirroring the columns and CHECK
 // ranges in migration 0056.
 type Settings struct {
-	Enabled          bool
-	GraceHours       int32
-	BackoffBaseHours int32
-	BackoffMaxHours  int32
-	MaxAttempts      int32
-	MaxPerPass       int32
-	AutoApprove      bool
+	Enabled    bool
+	GraceHours int32
+	MaxPerPass int32
 }
 
 // Defaults mirror migration 0056's column defaults. Duplicated here so a
@@ -38,13 +34,9 @@ type Settings struct {
 // zero-valued one — a zero grace window would fire on every transient
 // unmount, which is the exact failure the grace period exists to prevent.
 var Defaults = Settings{
-	Enabled:          true,
-	GraceHours:       24,
-	BackoffBaseHours: 6,
-	BackoffMaxHours:  168,
-	MaxAttempts:      3,
-	MaxPerPass:       20,
-	AutoApprove:      true,
+	Enabled:    true,
+	GraceHours: 24,
+	MaxPerPass: 20,
 }
 
 // ErrOutOfRange is returned by Set for values migration 0056's CHECKs would
@@ -92,13 +84,9 @@ func (s *SettingsService) Set(ctx context.Context, in Settings) (Settings, error
 		return Settings{}, err
 	}
 	row, err := dbq.New(s.pool).UpdateReacquisitionSettings(ctx, dbq.UpdateReacquisitionSettingsParams{
-		Enabled:          in.Enabled,
-		GraceHours:       in.GraceHours,
-		BackoffBaseHours: in.BackoffBaseHours,
-		BackoffMaxHours:  in.BackoffMaxHours,
-		MaxAttempts:      in.MaxAttempts,
-		MaxPerPass:       in.MaxPerPass,
-		AutoApprove:      in.AutoApprove,
+		Enabled:    in.Enabled,
+		GraceHours: in.GraceHours,
+		MaxPerPass: in.MaxPerPass,
 	})
 	if err != nil {
 		return Settings{}, fmt.Errorf("reacquisition: save settings: %w", err)
@@ -110,43 +98,10 @@ func (s *SettingsService) Set(ctx context.Context, in Settings) (Settings, error
 	return out, nil
 }
 
-// Backoff is how long to wait before the next attempt on an album that has
-// already been tried [attempts] times: base * 2^(attempts-1), clamped to the
-// configured maximum. Zero attempts means "never tried", which is always due.
-//
-// Exported and pure so the schedule is testable without a database, and so
-// the admin surface can show the same number the sweeper will act on.
-func (s Settings) Backoff(attempts int32) time.Duration {
-	if attempts <= 0 {
-		return 0
-	}
-	hours := s.BackoffBaseHours
-	for i := int32(1); i < attempts; i++ {
-		hours *= 2
-		// Clamp inside the loop as well as after: doubling from a large base
-		// enough times would overflow int32 before the comparison ran.
-		if hours >= s.BackoffMaxHours {
-			return time.Duration(s.BackoffMaxHours) * time.Hour
-		}
-	}
-	if hours > s.BackoffMaxHours {
-		hours = s.BackoffMaxHours
-	}
-	return time.Duration(hours) * time.Hour
-}
-
 func validate(in Settings) error {
 	switch {
 	case in.GraceHours < 1 || in.GraceHours > 720:
 		return fmt.Errorf("%w: grace_hours must be 1-720", ErrOutOfRange)
-	case in.BackoffBaseHours < 1 || in.BackoffBaseHours > 168:
-		return fmt.Errorf("%w: backoff_base_hours must be 1-168", ErrOutOfRange)
-	case in.BackoffMaxHours < 1 || in.BackoffMaxHours > 720:
-		return fmt.Errorf("%w: backoff_max_hours must be 1-720", ErrOutOfRange)
-	case in.BackoffMaxHours < in.BackoffBaseHours:
-		return fmt.Errorf("%w: backoff_max_hours must be >= backoff_base_hours", ErrOutOfRange)
-	case in.MaxAttempts < 1 || in.MaxAttempts > 10:
-		return fmt.Errorf("%w: max_attempts must be 1-10", ErrOutOfRange)
 	case in.MaxPerPass < 1 || in.MaxPerPass > 200:
 		return fmt.Errorf("%w: max_per_pass must be 1-200", ErrOutOfRange)
 	}
@@ -155,12 +110,8 @@ func validate(in Settings) error {
 
 func fromRow(row dbq.ReacquisitionSetting) Settings {
 	return Settings{
-		Enabled:          row.Enabled,
-		GraceHours:       row.GraceHours,
-		BackoffBaseHours: row.BackoffBaseHours,
-		BackoffMaxHours:  row.BackoffMaxHours,
-		MaxAttempts:      row.MaxAttempts,
-		MaxPerPass:       row.MaxPerPass,
-		AutoApprove:      row.AutoApprove,
+		Enabled:    row.Enabled,
+		GraceHours: row.GraceHours,
+		MaxPerPass: row.MaxPerPass,
 	}
 }