fix(download): honor explicitly selected provider

go_backend/extension_fallback.go

@@ -524,7 +524,12 @@ func DownloadWithExtensionFallback(req DownloadRequest) (*DownloadResponse, erro
 		}
 	}
 
-	priority = prioritizeFallbackProvidersByHealth(priority, extManager, req.Source)
+	healthProtectedProvider := selectedProvider
+	if strings.TrimSpace(healthProtectedProvider) == "" {
+		healthProtectedProvider = req.Source
+	}
+	priority = prioritizeFallbackProvidersByHealth(priority, extManager, healthProtectedProvider)
+	priority = moveProviderToFront(priority, selectedProvider)
 
 	for _, providerID := range priority {
 		if isDownloadCancelled(req.ItemID) {

go_backend/extension_fallback_helpers.go

@@ -280,7 +280,7 @@ func fallbackRuntimeHealthStatus(ext *loadedExtension) string {
 	}
 }
 
-func prioritizeFallbackProvidersByHealth(priority []string, extManager *extensionManager, sourceProvider string) []string {
+func prioritizeFallbackProvidersByHealth(priority []string, extManager *extensionManager, protectedProvider string) []string {
 	if len(priority) == 0 || extManager == nil {
 		return priority
 	}
@@ -294,7 +294,7 @@ func prioritizeFallbackProvidersByHealth(priority []string, extManager *extensio
 		if providerID == "" {
 			continue
 		}
-		if strings.EqualFold(providerID, sourceProvider) || !isExtensionFallbackAllowed(providerID) {
+		if strings.EqualFold(providerID, protectedProvider) || !isExtensionFallbackAllowed(providerID) {
 			unknown = append(unknown, providerID)
 			continue
 		}
@@ -324,6 +324,33 @@ func prioritizeFallbackProvidersByHealth(priority []string, extManager *extensio
 	return result
 }
 
+// moveProviderToFront preserves the user's explicit provider selection after
+// health-based fallback sorting. Health may order the remaining fallback
+// candidates, but it must never silently replace the provider the user picked.
+func moveProviderToFront(priority []string, providerID string) []string {
+	providerID = strings.TrimSpace(providerID)
+	if providerID == "" || len(priority) < 2 {
+		return priority
+	}
+
+	selectedIndex := -1
+	for i, candidate := range priority {
+		if strings.EqualFold(strings.TrimSpace(candidate), providerID) {
+			selectedIndex = i
+			break
+		}
+	}
+	if selectedIndex <= 0 {
+		return priority
+	}
+
+	reordered := make([]string, 0, len(priority))
+	reordered = append(reordered, priority[selectedIndex])
+	reordered = append(reordered, priority[:selectedIndex]...)
+	reordered = append(reordered, priority[selectedIndex+1:]...)
+	return reordered
+}
+
 func resolveExtensionAvailabilityReason(availability *ExtAvailabilityResult, err error) string {
 	if availability != nil {
 		if reason := strings.TrimSpace(availability.Reason); reason != "" {

go_backend/extension_providers_test.go

@@ -10,6 +10,7 @@ import (
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"sync"
 	"testing"
@@ -457,6 +458,19 @@ func TestShouldStopProviderFallback(t *testing.T) {
 	}
 }
 
+func TestMoveProviderToFrontPreservesExplicitSelection(t *testing.T) {
+	priority := []string{"qobuz-web", "amazon-web", "tidal-web"}
+	got := moveProviderToFront(priority, "AMAZON-WEB")
+	want := []string{"amazon-web", "qobuz-web", "tidal-web"}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("moveProviderToFront() = %#v, want %#v", got, want)
+	}
+	if !reflect.DeepEqual(priority, []string{"qobuz-web", "amazon-web", "tidal-web"}) {
+		t.Fatalf("moveProviderToFront mutated input: %#v", priority)
+	}
+}
+
 func TestBuildExtensionFallbackStoppedResponsePrefersAvailabilityReason(t *testing.T) {
 	resp := buildExtensionFallbackStoppedResponse("soundcloud", &ExtAvailabilityResult{
 		Reason:       "direct SoundCloud track ID",