fix(plugins): stop the cache janitor when a plugin cache is dropped

newCacheService started a ttlcache janitor goroutine that only stopped via the
explicit Close() path, so a cache service that was discarded without being closed
leaked its janitor for the process lifetime. It now registers the same
runtime.AddCleanup safety net that utils/cache.simpleCache already uses.

plugins/host_cache.go

@@ -2,6 +2,7 @@ package plugins
 
 import (
 	"context"
+	"runtime"
 	"time"
 
 	"github.com/jellydator/ttlcache/v3"
@@ -29,11 +30,18 @@ func newCacheService(pluginName string) *cacheServiceImpl {
 	// Start the janitor goroutine to clean up expired entries
 	go cache.Start()
 
-	return &cacheServiceImpl{
+	svc := &cacheServiceImpl{
 		pluginName: pluginName,
 		cache:      cache,
 		defaultTTL: defaultCacheTTL,
 	}
+
+	// Automatic cleanup to prevent goroutine leak when the service is garbage collected
+	runtime.AddCleanup(svc, func(ttlCache *ttlcache.Cache[string, any]) {
+		ttlCache.Stop()
+	}, cache)
+
+	return svc
 }
 
 // getTTL converts seconds to a duration, using default if 0 or negative

plugins/host_cache_test.go

@@ -8,9 +8,11 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"net/http"
 	"os"
 	"path/filepath"
+	"runtime"
 	"time"
 
 	"github.com/navidrome/navidrome/conf"
@@ -599,3 +601,39 @@ var _ = Describe("CacheService Integration", Ordered, func() {
 		})
 	})
 })
+
+var _ = Describe("newCacheService", func() {
+	// Background goroutines wind down late, so poll for two consecutive equal samples.
+	settleGoroutines := func() int {
+		prev := -1
+		for range 100 {
+			runtime.GC()
+			n := runtime.NumGoroutine()
+			if n == prev {
+				return n
+			}
+			prev = n
+			time.Sleep(10 * time.Millisecond)
+		}
+		return prev
+	}
+
+	It("stops the janitor goroutine once the service is unreachable", func() {
+		const numServices = 20
+
+		baseline := settleGoroutines()
+
+		services := make([]*cacheServiceImpl, 0, numServices)
+		for i := range numServices {
+			services = append(services, newCacheService(fmt.Sprintf("plugin_%d", i)))
+		}
+		Expect(runtime.NumGoroutine()).To(BeNumerically(">=", baseline+numServices),
+			"expected one janitor goroutine per cache service")
+
+		services = nil
+		Expect(services).To(BeNil())
+
+		Expect(settleGoroutines()).To(BeNumerically("<", baseline+numServices),
+			"janitor goroutines leaked after the services became unreachable")
+	})
+})