feat(server/coverart): auto-bump version on registered-provider change

On boot, the SettingsService computes a SHA-256 hash of the sorted
registered-provider IDs and compares to the hash stored on
cover_art_sources_meta. Mismatch → atomic bump of current_version +
update of stored hash. The next enrichment pass picks up the new
version, all 'none' rows become eligible, and they get retried
against the new chain (now including Deezer / Last.fm).

One-shot: subsequent boots without a provider-set change don't bump
again. The check is best-effort — failures are logged at Warn but
don't refuse startup; a temporarily unreachable DB at boot just
means 'none' rows stay parked until a manual re-search (next task).

Tests cover first-boot (empty stored hash → bump), repeat-boot
(no change → no bump), and the registered-providers-hash
determinism.

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

internal/coverart/settings.go

@@ -2,6 +2,8 @@ package coverart
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"log/slog"
 	"sort"
@@ -261,6 +263,54 @@ func enabledSetSignature(enabledIDs map[string]bool) string {
 	return strings.Join(ids, ",")
 }
 
+// BumpVersionIfProvidersChanged compares the current registered-provider
+// set (by ID) to the last set seen on a prior successful boot. If
+// different, it atomically increments cover_art_sources_meta.current_version
+// and stores the new hash, returning (newVersion, true, nil). If
+// unchanged, returns (currentVersion, false, nil) without touching the DB.
+//
+// Used at boot to ensure rows previously settled to 'none' get re-tried
+// once after a provider chain change (e.g. operator updates the binary
+// and a new provider is registered, or one is removed). The version
+// bump triggers eligibility for 'none' rows on the next enrichment pass
+// without requiring a manual operator action.
+func (s *SettingsService) BumpVersionIfProvidersChanged(ctx context.Context) (version int32, bumped bool, err error) {
+	hash := registeredProvidersHash()
+	q := dbq.New(s.pool)
+
+	stored, qerr := q.GetCoverArtProvidersHash(ctx)
+	if qerr != nil {
+		return 0, false, fmt.Errorf("get providers hash: %w", qerr)
+	}
+	if stored == hash {
+		return s.CurrentVersion(), false, nil
+	}
+
+	newVer, berr := q.BumpVersionAndSetProvidersHash(ctx, hash)
+	if berr != nil {
+		return 0, false, fmt.Errorf("bump version: %w", berr)
+	}
+	// Update the in-memory version so the next enrichment pass sees the new value.
+	s.mu.Lock()
+	s.currentVersion = newVer
+	s.mu.Unlock()
+	return newVer, true, nil
+}
+
+// registeredProvidersHash returns the SHA-256 hex of the sorted,
+// colon-joined registered provider IDs.
+func registeredProvidersHash() string {
+	provs := AllProviders()
+	ids := make([]string, 0, len(provs))
+	for _, p := range provs {
+		ids = append(ids, p.ID())
+	}
+	sort.Strings(ids)
+	joined := strings.Join(ids, ":")
+	sum := sha256.Sum256([]byte(joined))
+	return hex.EncodeToString(sum[:])
+}
+
 // TestProvider invokes TestConnection on the named provider if it
 // implements TestableProvider. Returns ErrNotTestable if the
 // provider doesn't, ErrProviderNotFound if not registered.