fix(plugins): resolve race condition in plugin manager registration

Fixed a race condition in the plugin manager where goroutines started during
plugin registration could concurrently access shared plugin maps while the
main registration loop was still running. The fix separates plugin registration
from background processing by collecting all plugins first, then starting
background goroutines after registration is complete.

This prevents concurrent read/write access to the plugins and adapters maps
that was causing data races detected by the Go race detector. The solution
maintains the same functionality while ensuring thread safety during the
plugin scanning and registration process.

Signed-off-by: Deluan <deluan@navidrome.org>

plugins/manager.go

@@ -189,13 +189,6 @@ func (m *managerImpl) registerPlugin(pluginID, pluginDir, wasmPath string, manif
 	}
 	m.mu.Unlock()
 
-	// Start pre-compilation of WASM module in background AFTER registration
-	go func() {
-		precompilePlugin(p)
-		// Check if this plugin implements InitService and hasn't been initialized yet
-		m.initializePluginIfNeeded(p)
-	}()
-
 	log.Info("Discovered plugin", "folder", pluginID, "name", manifest.Name, "capabilities", manifest.Capabilities, "wasm", wasmPath, "dev_mode", isSymlink)
 	return m.plugins[pluginID]
 }
@@ -261,6 +254,7 @@ func (m *managerImpl) ScanPlugins() {
 	discoveries := DiscoverPlugins(root)
 
 	var validPluginNames []string
+	var registeredPlugins []*plugin
 	for _, discovery := range discoveries {
 		if discovery.Error != nil {
 			// Handle global errors (like directory read failure)
@@ -284,7 +278,20 @@ func (m *managerImpl) ScanPlugins() {
 		validPluginNames = append(validPluginNames, discovery.ID)
 
 		// Register the plugin
-		m.registerPlugin(discovery.ID, discovery.Path, discovery.WasmPath, discovery.Manifest)
+		plugin := m.registerPlugin(discovery.ID, discovery.Path, discovery.WasmPath, discovery.Manifest)
+		if plugin != nil {
+			registeredPlugins = append(registeredPlugins, plugin)
+		}
+	}
+
+	// Start background processing for all registered plugins after registration is complete
+	// This avoids race conditions between registration and goroutines that might unregister plugins
+	for _, p := range registeredPlugins {
+		go func(plugin *plugin) {
+			precompilePlugin(plugin)
+			// Check if this plugin implements InitService and hasn't been initialized yet
+			m.initializePluginIfNeeded(plugin)
+		}(p)
 	}
 
 	log.Debug("Found valid plugins", "count", len(validPluginNames), "plugins", validPluginNames)