Only use the appGroupTemporaryDirectory to access a file from the share extension. (#4002)

… and switch back to the plain `URL.temporaryDirectory` for everything else.

* Fix documentation

Co-authored-by: Stefan Ceriu <stefan.ceriu@gmail.com>

ElementX/Sources/Application/AppCoordinator.swift

@@ -125,6 +125,9 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
         
         if let previousVersion = appSettings.lastVersionLaunched.flatMap(Version.init) {
             performMigrationsIfNecessary(from: previousVersion, to: currentVersion)
+            
+            // Manual clean to handle the potential case where the app crashes before moving a shared file.
+            cleanAppGroupTemporaryDirectory()
         } else {
             // The app has been deleted since the previous run. Reset everything.
             wipeUserData(includingSettings: true)
@@ -252,12 +255,17 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
                 } else {
                     handleAppRoute(.childEventOnRoomAlias(eventID: eventID, alias: alias))
                 }
-            case .share:
+            case .share(let payload):
                 guard isExternalURL else {
                     MXLog.error("Received unexpected internal share route")
                     break
                 }
-                handleAppRoute(route)
+                
+                do {
+                    try handleAppRoute(.share(payload.withDefaultTemporaryDirectory()))
+                } catch {
+                    MXLog.error("Failed moving payload out of the app group container: \(error)")
+                }
             default:
                 break
             }
@@ -408,6 +416,31 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
         userSessionStore.reset()
     }
     
+    /// Manually cleans up any files in the app group's `tmp` directory.
+    ///
+    /// **Note:** If there is a single file we consider it to be an active share payload and ignore it.
+    private func cleanAppGroupTemporaryDirectory() {
+        let fileURLs: [URL]
+        do {
+            fileURLs = try FileManager.default.contentsOfDirectory(at: URL.appGroupTemporaryDirectory, includingPropertiesForKeys: nil, options: [])
+        } catch {
+            MXLog.warning("Failed to enumerate app group temporary directory: \(error)")
+            return
+        }
+        
+        guard fileURLs.count > 1 else {
+            return // If there is only a single item in here, there's likely a pending share payload that is yet to be processed.
+        }
+        
+        for url in fileURLs {
+            do {
+                try FileManager.default.removeItem(at: url)
+            } catch {
+                MXLog.warning("Failed to remove file from app group temporary directory: \(error)")
+            }
+        }
+    }
+    
     private func setupStateMachine() {
         stateMachine.addTransitionHandler { [weak self] context in
             guard let self else { return }