tweak createForExternal

Co-authored-by: adbenitez <24558636+adbenitez@users.noreply.github.com>

src/main/java/org/thoughtcrime/securesms/providers/PersistentBlobProvider.java

@@ -122,8 +122,26 @@ public class PersistentBlobProvider {
   }
 
   public Uri createForExternal(@NonNull Context context, @NonNull String mimeType) throws IOException, IllegalStateException, NullPointerException {
-    File target = new File(getExternalDir(context), System.currentTimeMillis() + "." + getExtensionFromMimeType(mimeType));
-    return FileProviderUtil.getUriFor(context, target);
+    String filename = System.currentTimeMillis() + "." + getExtensionFromMimeType(mimeType);
+    
+    // Try external cache first
+    try {
+      File externalDir = getExternalDir(context);
+      File target = new File(externalDir, filename);
+      return FileProviderUtil.getUriFor(context, target);
+    } catch (IllegalArgumentException e) {
+      // FileProvider doesn't support the external cache path (e.g., on removable SD card).
+      // Note: getExternalDir() already falls back to internal cache when external cache is null,
+      // but when external cache exists on a removable SD card, FileProvider may reject it.
+      // In that case, we explicitly use internal cache which FileProvider always supports.
+      Log.w(TAG, "FileProvider doesn't support external cache path, falling back to internal cache", e);
+      File internalDir = context.getCacheDir();
+      if (internalDir == null) {
+        throw new IOException("no cache directory available");
+      }
+      File target = new File(internalDir, filename);
+      return FileProviderUtil.getUriFor(context, target);
+    }
   }
 
   public boolean delete(@NonNull Context context, @NonNull Uri uri) {

src/main/res/xml/file_provider_paths.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <paths>
+    <cache-path name="cache" path="." />
     <external-cache-path name="external_cache" path="." />
     <external-files-path name="external_files" path="." />