feat(api): admin endpoints for the re-acquisition policy — #2527

GET/PUT /api/admin/library/reacquisition, so every knob the sweeper
reads is editable without a restart (rule #25). Routed under /library
beside the missing-files list it governs rather than under /lidarr:
Lidarr is the mechanism, but missing files are the problem the operator
came to solve, and that is the surface they meet it on.

The payload carries one thing the settings table doesn't: the count of
albums with missing files that can never be auto-requested, because
neither they nor their artist has an MBID. Nothing can be asked of
Lidarr for a release MusicBrainz cannot name, and a feature that
silently does nothing for part of its input reads as broken -- so the
card states the number instead of leaving it to be inferred. Counted
best-effort: the settings are the point of the endpoint, and failing the
whole card because a count query hiccuped would be the wrong trade.

Range errors come back as 400 naming the field. The Go-side validation
mirrors migration 0056's CHECKs precisely so the operator reads
"grace_hours must be 1-720" rather than a constraint-violation string
surfacing as a 500.

internal/api/api.go

@@ -23,6 +23,7 @@ import (
 	"git.fabledsword.com/bvandeusen/minstrel/internal/netsettings"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playevents"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playlists"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/reacquisition"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/recsettings"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/tags"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/tracks"
@@ -31,7 +32,7 @@ import (
 // Mount attaches /api/* handlers to r. Public endpoints (login) are outside
 // RequireUser; everything else is gated by the middleware. The events writer
 // is shared with the Subsonic mount so /rest/scrobble feeds the same store.
-func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, recSettings *recsettings.Service, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, tagSettings *tags.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler, streamSecret []byte, netSettings *netsettings.Service) {
+func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, recSettings *recsettings.Service, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, tagSettings *tags.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler, streamSecret []byte, netSettings *netsettings.Service, reacqSettings *reacquisition.SettingsService) {
 	rng := rand.New(rand.NewSource(rand.Int63()))
 	h := &handlers{
 		pool: pool, logger: logger, events: events, recCfg: recCfg,
@@ -53,6 +54,7 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 		playlistScheduler: playlistScheduler,
 		streamSecret:      streamSecret,
 		netSettings:       netSettings,
+		reacqSettings:     reacqSettings,
 	}
 
 	r.Route("/api", func(api chi.Router) {
@@ -195,6 +197,13 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 				admin.Get("/network-settings", h.handleGetNetworkSettings)
 				admin.Put("/network-settings", h.handleUpdateNetworkSettings)
 
+				// Policy for turning a missing file back into a Lidarr
+				// request (#290). Sits beside the missing-files list it
+				// governs rather than under /lidarr, because the operator
+				// meets it on the missing-files surface.
+				admin.Get("/library/reacquisition", h.handleGetReacquisitionSettings)
+				admin.Put("/library/reacquisition", h.handleUpdateReacquisitionSettings)
+
 				admin.Get("/scan/status", h.handleGetScanStatus)
 				admin.Post("/scan/run", h.handleTriggerScan)
 				// Sits under /library rather than /tracks because what it
@@ -279,6 +288,10 @@ type handlers struct {
 	mailer            mailer.Sender
 	eventbus          *eventbus.Bus
 	playlistScheduler *playlists.Scheduler
+	// reacqSettings is the DB-backed policy for auto re-acquisition of
+	// missing files (milestone #290) — grace window, backoff, attempt caps.
+	// Cached in the service, so the admin card reads it without a query.
+	reacqSettings *reacquisition.SettingsService
 	// netSettings caches the trusted reverse-proxy depth read by the auth
 	// middleware on every request and edited from the admin network card.
 	netSettings *netsettings.Service