Recognise dragged iOS screenshots as images instead of raw data

When dragging the floating screenshot preview into a room, iOS hands us
a provider whose `suggestedName` is e.g. `Screenshot 2026-05-22 at
14.49.40`. `NSString.pathExtension` returns `"40"`, so the previous
`!pathExtension.isEmpty` check treated the timestamp's trailing segment
as a real extension. The file got written without `.jpg`/`.png`, and the
`MediaUploadingPreprocessor` then fell back to `application/octet-stream`
which is why screenshots showed up as a "data" tile.

ElementX.xcodeproj/project.pbxproj

@@ -221,6 +221,7 @@
 		22C5483D01EEB290B8339817 /* HomeScreenInviteCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D8FC33C3F6BF597E095CE9FA /* HomeScreenInviteCell.swift */; };
 		2335D1AB954C151FD8779F45 /* RoomPermissionsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = F0096BC5DA86AF6B6E5742AC /* RoomPermissionsTests.swift */; };
 		23701DE32ACD6FD40AA992C3 /* MediaUploadingPreprocessorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = AE203026B9AD3DB412439866 /* MediaUploadingPreprocessorTests.swift */; };
+		5C0EE5C0EE5C0EE5C0EE5C01 /* NSItemProviderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5C0EE5C0EE5C0EE5C0EE5C02 /* NSItemProviderTests.swift */; };
 		237FC70AA257B935F53316BA /* SessionVerificationControllerProxy.swift in Sources */ = {isa = PBXBuildFile; fileRef = C55D7E514F9DE4E3D72FDCAD /* SessionVerificationControllerProxy.swift */; };
 		238D561CA231339C6D4D06F3 /* ClientBuilder.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A1C33355FFB0F0953C35036 /* ClientBuilder.swift */; };
 		23E23736B53946785431A74F /* AppAppearance.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0FD22AEFFA20065494ED2333 /* AppAppearance.swift */; };
@@ -2622,6 +2623,7 @@
 		AD9CB3B9DFA353AB2B7CD9F8 /* NotificationSettingsEditScreenCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NotificationSettingsEditScreenCoordinator.swift; sourceTree = "<group>"; };
 		ADCB8A232D3A8FB3E16A7303 /* uk */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = uk; path = uk.lproj/Localizable.strings; sourceTree = "<group>"; };
 		AE203026B9AD3DB412439866 /* MediaUploadingPreprocessorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MediaUploadingPreprocessorTests.swift; sourceTree = "<group>"; };
+		5C0EE5C0EE5C0EE5C0EE5C02 /* NSItemProviderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NSItemProviderTests.swift; sourceTree = "<group>"; };
 		AE40D4A5DD857AC16EED945A /* URLSession.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = URLSession.swift; sourceTree = "<group>"; };
 		AE52983FAFB4E0998C00EE8A /* CancellableTask.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CancellableTask.swift; sourceTree = "<group>"; };
 		AE5DDBEBBA17973ED4638823 /* de */ = {isa = PBXFileReference; lastKnownFileType = text.plist.stringsdict; name = de; path = de.lproj/Localizable.stringsdict; sourceTree = "<group>"; };
@@ -4968,6 +4970,7 @@
 				2D7A2C4A3A74F0D2FFE9356A /* MediaPlayerProviderTests.swift */,
 				AE203026B9AD3DB412439866 /* MediaUploadingPreprocessorTests.swift */,
 				03FABD73FD8086EFAB699F42 /* MediaUploadPreviewScreenViewModelTests.swift */,
+				5C0EE5C0EE5C0EE5C0EE5C02 /* NSItemProviderTests.swift */,
 				6F6E6EDC4BBF962B2ED595A4 /* MessageForwardingScreenViewModelTests.swift */,
 				F875D71347DC81EAE7687446 /* NavigationRootCoordinatorTests.swift */,
 				78913D6E120D46138E97C107 /* NavigationSplitCoordinatorTests.swift */,
@@ -7952,6 +7955,7 @@
 				167D00CAA13FAFB822298021 /* MediaProviderTests.swift in Sources */,
 				B9A8C34A00D03094C0CF56F3 /* MediaUploadPreviewScreenViewModelTests.swift in Sources */,
 				23701DE32ACD6FD40AA992C3 /* MediaUploadingPreprocessorTests.swift in Sources */,
+				5C0EE5C0EE5C0EE5C0EE5C01 /* NSItemProviderTests.swift in Sources */,
 				F777C6FEE7D106136E2ED2B2 /* MessageForwardingScreenViewModelTests.swift in Sources */,
 				1146E9EDCF8344F7D6E0D553 /* MockCoder.swift in Sources */,
 				DC68E866D6E664B0D2B06E74 /* MockImageCache.swift in Sources */,

ElementX/Sources/Other/Extensions/NSItemProvider.swift

@@ -196,8 +196,15 @@ extension NSItemProvider {
     }
 }
 
-private extension NSString {
+extension NSString {
+    /// `NSString.pathExtension` returns the trailing dot-segment regardless of whether
+    /// it's a real extension, and `UTType(filenameExtension:)` synthesises a `dyn.*`
+    /// placeholder for unknown ones instead of returning nil — so check both.
     var hasPathExtension: Bool {
-        !pathExtension.isEmpty
+        guard !pathExtension.isEmpty,
+              let type = UTType(filenameExtension: pathExtension) else {
+            return false
+        }
+        return !type.isDynamic
     }
 }

UnitTests/Sources/NSItemProviderTests.swift

@@ -0,0 +1,71 @@
+//
+// Copyright 2026 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+// Please see LICENSE files in the repository root for full details.
+//
+
+@testable import ElementX
+import Foundation
+import Testing
+
+struct NSItemProviderTests {
+    // MARK: - hasPathExtension
+
+    @Test
+    func hasPathExtensionRecognisesRegisteredExtensions() {
+        #expect(("IMG_1234.jpg" as NSString).hasPathExtension)
+        #expect(("photo.png" as NSString).hasPathExtension)
+        #expect(("clip.heic" as NSString).hasPathExtension)
+        #expect(("doc.pdf" as NSString).hasPathExtension)
+    }
+
+    @Test
+    func hasPathExtensionRejectsDateLikeTrailingSegments() {
+        // iOS screenshot drags expose a `suggestedName` like
+        // `Screenshot 2026-05-22 at 14.49.40`, whose `pathExtension` is `"40"`.
+        // `UTType(filenameExtension:)` synthesises a `dyn.*` placeholder for that —
+        // it must not be treated as a real extension.
+        #expect(!("Screenshot 2026-05-22 at 14.49.40" as NSString).hasPathExtension)
+        #expect(!("report 2025.10" as NSString).hasPathExtension)
+        #expect(!("v1.2.3" as NSString).hasPathExtension)
+    }
+
+    @Test
+    func hasPathExtensionRejectsAbsentExtension() {
+        #expect(!("plainname" as NSString).hasPathExtension)
+        #expect(!("" as NSString).hasPathExtension)
+        #expect(!("trailing dot." as NSString).hasPathExtension)
+    }
+
+    // MARK: - storeData()
+
+    @Test
+    func storeDataAppendsExtensionWhenSuggestedNameLooksLikeAScreenshot() async throws {
+        let imageURL = try #require(Bundle(for: BundleAnchor.self).url(forResource: "test_image.png", withExtension: nil),
+                                    "Failed retrieving fixture")
+        let provider = try #require(NSItemProvider(contentsOf: imageURL))
+        provider.suggestedName = "Screenshot 2026-05-22 at 14.49.40"
+
+        let storedURL = try #require(await provider.storeData())
+
+        #expect(storedURL.pathExtension == "png")
+        #expect(storedURL.deletingPathExtension().lastPathComponent == "Screenshot 2026-05-22 at 14.49.40")
+    }
+
+    @Test
+    func storeDataPreservesSuggestedNameWithRealExtension() async throws {
+        let imageURL = try #require(Bundle(for: BundleAnchor.self).url(forResource: "test_image.png", withExtension: nil),
+                                    "Failed retrieving fixture")
+        let provider = try #require(NSItemProvider(contentsOf: imageURL))
+        provider.suggestedName = "IMG_1234.png"
+
+        let storedURL = try #require(await provider.storeData())
+
+        #expect(storedURL.lastPathComponent == "IMG_1234.png")
+    }
+}
+
+/// `Bundle(for:)` requires a class; the enclosing test type is a struct, so we keep
+/// a private anchor to scope the lookup to the unit test bundle.
+private final class BundleAnchor { }