Add real-world large-file test (multi-GB from phone via external URL, chunked)

Opt-in (-e bigFileMB=<size>): streams a multi-GB file from the device through
the app's chunked-upload path to the external nextcloud.khodak.me and verifies
the full size lands. Verified live: 1.5 GB and 5 GB both succeed end-to-end.

app/src/androidTest/kotlin/com/syncflow/NextcloudIntegrationTest.kt

@@ -22,6 +22,9 @@ import org.junit.Test
 import org.junit.runner.RunWith
 import java.io.ByteArrayInputStream
 import java.io.ByteArrayOutputStream
+import java.io.File
+import java.io.FileInputStream
+import java.io.FileOutputStream
 import java.time.Instant
 
 /**
@@ -37,6 +40,7 @@ import java.time.Instant
 @RunWith(AndroidJUnit4::class)
 class NextcloudIntegrationTest {
 
+    private val ctx = InstrumentationRegistry.getInstrumentation().targetContext
     private val args = InstrumentationRegistry.getArguments()
     private val url = args.getString("ncUrl")
     private val user = args.getString("ncUser")
@@ -138,4 +142,44 @@ class NextcloudIntegrationTest {
             runCatching { p.deleteFile(dir) }
         }
     }
+
+    /**
+     * Real-world large-file test: streams a multi-GB file FROM THE PHONE through the app's
+     * chunked-upload path to the external URL, verifies the full size landed, then cleans up.
+     * Opt-in (slow): pass -e bigFileMB=<size>, e.g. 1536 for 1.5 GB.
+     */
+    @Test
+    fun realWorld_largeFileChunkedUpload() = runBlocking {
+        assumeTrue("ncUrl/ncUser/ncPass required", url != null && user != null && pass != null)
+        val mb = args.getString("bigFileMB")?.toIntOrNull() ?: 0
+        assumeTrue("pass -e bigFileMB=<size> to run the big-file test", mb > 0)
+
+        val account = CloudAccount(
+            id = 1, displayName = "IT", email = user, providerType = ProviderType.NEXTCLOUD,
+            credentialJson = """{"username":"$user","password":"$pass"}""", serverUrl = url, port = null,
+        )
+        val p = NextcloudProvider(account) // default 100 MB chunks -> chunked path for >100 MB
+        val dir = "SyncFlowBig_${System.currentTimeMillis()}"
+        val tmp = File(ctx.cacheDir, "bigfile_${System.currentTimeMillis()}.bin")
+        try {
+            val total = mb.toLong() * 1024 * 1024
+            FileOutputStream(tmp).use { os ->
+                val buf = ByteArray(8 * 1024 * 1024)
+                var written = 0L
+                while (written < total) {
+                    val n = minOf(buf.size.toLong(), total - written).toInt()
+                    os.write(buf, 0, n); written += n
+                }
+            }
+            assertEquals(total, tmp.length())
+            p.createDirectory(dir).getOrThrow()
+            val up = p.uploadFile(FileInputStream(tmp), "$dir/big.bin", tmp.length())
+            assertTrue("large chunked upload failed: ${up.exceptionOrNull()}", up.isSuccess)
+            assertEquals("full file size must land on the server", total,
+                p.listFiles(dir).getOrThrow().first { it.name == "big.bin" }.sizeBytes)
+        } finally {
+            tmp.delete()
+            runCatching { p.deleteFile(dir) }
+        }
+    }
 }