diff --git a/Yattee/Core/AppEnvironment.swift b/Yattee/Core/AppEnvironment.swift
index dd95cb6b..8f00049e 100644
--- a/Yattee/Core/AppEnvironment.swift
+++ b/Yattee/Core/AppEnvironment.swift
@@ -56,6 +56,21 @@ final class AppEnvironment {
     let legacyMigrationService: LegacyDataMigrationService
     let sourcesSettings: SourcesSettings
 
+    // MARK: - Shared Instance
+
+    /// The single, process-wide app environment.
+    ///
+    /// SwiftUI may evaluate a `@State` property's default-value autoclosure more
+    /// than once (it keeps only the first result but still runs the side effects
+    /// of the discarded instances). Constructing `AppEnvironment` more than once
+    /// would create multiple `DownloadManager`s — and therefore multiple
+    /// background `URLSession`s registered under the same identifier — causing
+    /// download-completion delegate callbacks to be delivered to an instance
+    /// whose `activeDownloads` is empty (the finished file is then dropped).
+    /// Referencing this `static let` from the App's `@State` guarantees exactly
+    /// one instance for the lifetime of the process.
+    static let shared = AppEnvironment()
+
     // MARK: - Initialization
 
     init(
diff --git a/Yattee/Services/Downloads/DownloadManager+Persistence.swift b/Yattee/Services/Downloads/DownloadManager+Persistence.swift
index 70dfb7dd..764ff525 100644
--- a/Yattee/Services/Downloads/DownloadManager+Persistence.swift
+++ b/Yattee/Services/Downloads/DownloadManager+Persistence.swift
@@ -71,7 +71,7 @@ extension DownloadManager {
 
     func loadDownloads() {
         let decoder = JSONDecoder()
-        
+
         // ==== ACTIVE DOWNLOADS ====
         if let activeData = UserDefaults.standard.data(forKey: "activeDownloads") {
             LoggingService.shared.logDownload(
diff --git a/Yattee/Services/Downloads/DownloadManager.swift b/Yattee/Services/Downloads/DownloadManager.swift
index b49aed0d..fc406c7f 100644
--- a/Yattee/Services/Downloads/DownloadManager.swift
+++ b/Yattee/Services/Downloads/DownloadManager.swift
@@ -146,10 +146,14 @@ final class DownloadManager: NSObject {
     func setDownloadSettings(_ settings: DownloadSettings) {
         let isInitialSetup = self.downloadSettings == nil
         self.downloadSettings = settings
-        // Invalidate old session before creating new one with correct settings
-        urlSession?.invalidateAndCancel()
-        urlSession = nil
-        setupSession()
+
+        // Create the background session only once. The background URLSession's
+        // identifier is process-global, so tearing it down here would cancel any
+        // in-flight downloads. Cellular-access changes are handled separately via
+        // refreshCellularAccessSetting(), which migrates active downloads safely.
+        if urlSession == nil {
+            setupSession()
+        }
 
         // Resume interrupted downloads only on initial setup
         if isInitialSetup {
diff --git a/Yattee/YatteeApp.swift b/Yattee/YatteeApp.swift
index 213bf74b..f2131ef7 100644
--- a/Yattee/YatteeApp.swift
+++ b/Yattee/YatteeApp.swift
@@ -27,7 +27,7 @@ struct YatteeApp: App {
     @NSApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
     #endif
 
-    @State private var appEnvironment = AppEnvironment()
+    @State private var appEnvironment = AppEnvironment.shared
     @State private var backgroundTasksRegistered = false
     @State private var showingClipboardAlert = false
     @State private var detectedClipboardURL: URL?