fix(hls): master playlist URL had ..m3u8 double extension

Root cause: Android's MimeTypeMap does not know
application/vnd.apple.mpegurl, so Nip96Uploader.upload() resolved the
extension to "" and sent the multipart filename as "abc." (trailing
dot). The NIP-96 server then echoed the upload name into its returned
URL, which arrived at the pipeline ending in ".". The pipeline's
withExtensionHint helper appended ".m3u8" on top of that, producing
"..m3u8" — which the subsequent playback GET 404s against because the
server stored the file at the single-dot path.

Two fixes, both needed:

1. Nip96Uploader.upload(InputStream, ...) now falls back to a small
   static MIME->extension table when MimeTypeMap returns null, covering
   the HLS playlist types and video/mp4 / fMP4 segment types. The file
   is uploaded with a real ".m3u8" / ".mp4" extension, so the server
   never has to invent one.

2. HlsUploadPipeline.withExtensionHint now trims trailing dots and
   collapses any existing "..ext" sequences before checking whether to
   append, so a server that still echoes a single trailing dot cannot
   produce unreachable URLs.

Regression test locks in that a fake uploader returning a
"https://server/bare-1." URL yields a single-dot ".m3u8" in the final
upload result.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

amethyst/src/main/java/com/vitorpamplona/amethyst/service/uploads/hls/HlsUploadPipeline.kt

@@ -126,7 +126,9 @@ class HlsUploadPipeline(
 
     // Blossom servers typically return bare-hash URLs (https://server/<sha256>), but HLS parsers
     // and ExoPlayer's Util.inferContentType sniff the URL extension to pick the right source
-    // factory. Append a hint unless the upload server already baked one in.
+    // factory. Append a hint unless the upload server already baked one in. Trailing dots are
+    // trimmed and any pre-existing doubled extension (e.g. "..m3u8") collapsed, so a server that
+    // echoes our empty-extension upload filename does not produce unreachable URLs.
     private fun withExtensionHint(
         url: String,
         contentType: String,
@@ -137,7 +139,11 @@ class HlsUploadPipeline(
                 CONTENT_TYPE_HLS -> ".m3u8"
                 else -> return url
             }
-        return if (url.endsWith(ext, ignoreCase = true)) url else url + ext
+        val sanitised =
+            url
+                .replace(Regex("""\.{2,}""" + Regex.escape(ext.trimStart('.')) + "$", RegexOption.IGNORE_CASE), ext)
+                .trimEnd('.')
+        return if (sanitised.endsWith(ext, ignoreCase = true)) sanitised else sanitised + ext
     }
 
     companion object {

amethyst/src/main/java/com/vitorpamplona/amethyst/service/uploads/nip96/Nip96Uploader.kt

@@ -144,7 +144,10 @@ class Nip96Uploader {
         checkNotInMainThread()
 
         val fileName = RandomInstance.randomChars(16)
-        val extension = contentType?.let { MimeTypeMap.getSingleton().getExtensionFromMimeType(it) } ?: ""
+        val extension =
+            contentType?.let {
+                MimeTypeMap.getSingleton().getExtensionFromMimeType(it) ?: fallbackExtensionForMimeType(it)
+            } ?: ""
 
         val client = okHttpClient(server.apiUrl)
         val requestBuilder = Request.Builder()
@@ -231,6 +234,18 @@ class Nip96Uploader {
 
     fun String.displayUrl() = this.removeSuffix("/").removePrefix("https://")
 
+    // Android's MimeTypeMap does not know every MIME we upload (notably HLS playlist types).
+    // When it returns null we fall back to a small static table so the multipart filename still
+    // carries a real extension — otherwise the server gets "name." and echoes it back, which
+    // breaks HLS URL rewriting.
+    private fun fallbackExtensionForMimeType(mimeType: String): String? =
+        when (mimeType.lowercase()) {
+            "application/vnd.apple.mpegurl", "application/x-mpegurl", "audio/x-mpegurl", "audio/mpegurl" -> "m3u8"
+            "video/mp2t" -> "ts"
+            "video/iso.segment", "video/mp4" -> "mp4"
+            else -> null
+        }
+
     fun convertToMediaResult(nip96: PartialEvent): MediaUploadResult {
         // Images don't seem to be ready immediately after upload
         val imageUrl = nip96.tags?.firstOrNull { it.size > 1 && it[0] == "url" }?.get(1)

amethyst/src/test/java/com/vitorpamplona/amethyst/service/uploads/hls/HlsUploadPipelineTest.kt

@@ -212,6 +212,32 @@ class HlsUploadPipelineTest {
         assertEquals("https://blossom.test/bare-1.mp4", result.renditions[0].combinedUrl)
     }
 
+    @Test
+    fun trailingDotUrlsAreSanitisedIntoCleanExtension() {
+        val bundle = createBundle(listOf("360p"))
+        val uploader =
+            object : HlsBlobUploader {
+                var count = 0
+
+                override suspend fun upload(
+                    file: File,
+                    contentType: String,
+                ): MediaUploadResult {
+                    count++
+                    return MediaUploadResult(url = "https://blossom.test/bare-$count.", sha256 = "sha-$count", size = file.length())
+                }
+            }
+        val pipeline = HlsUploadPipeline(uploader)
+
+        val result = runBlocking { pipeline.upload(bundle) }
+
+        assertTrue("masterUrl must not contain '..': ${result.masterUrl}", !result.masterUrl.contains(".."))
+        assertTrue("masterUrl must not end with '.': ${result.masterUrl}", !result.masterUrl.endsWith("."))
+        assertTrue(result.masterUrl.endsWith(".m3u8"))
+        assertTrue(!result.renditions[0].combinedUrl.contains(".."))
+        assertTrue(result.renditions[0].combinedUrl.endsWith(".mp4"))
+    }
+
     @Test
     fun doesNotDoubleAppendExtensionWhenAlreadyPresent() {
         val bundle = createBundle(listOf("360p"))