perf: tune image/video OkHttp dispatcher and connection pool

OkHttp's default dispatcher caps inflight requests per host at 5 and
total inflight at 64. Amethyst feeds typically pull most media from a
single host (e.g. a primary Blossom/imgproxy server), so that per-host
cap serialized feed loading — the browser-feels-faster effect.

- Give the images/videos factory a dedicated Dispatcher (16 per host,
  128 total on device; 5/64 on emulator).
- Give it a larger ConnectionPool (32 idle, 5 min keep-alive) so HTTP/2
  connections to the common media host stay warm across scrolls and
  avoid repeated TLS handshakes.
- Extract isEmulator() to a shared helper used by both the relay and
  image/video factories.

The relay factory is untouched (already tuned for websockets).

https://claude.ai/code/session_01PUbqGyUc6oq6V1MdmLi8sw

amethyst/src/main/java/com/vitorpamplona/amethyst/service/okhttp/IsEmulator.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.service.okhttp
+
+import android.os.Build
+
+internal fun isEmulator(): Boolean =
+    Build.FINGERPRINT.startsWith("generic") ||
+        Build.FINGERPRINT.lowercase().contains("emulator") ||
+        Build.MODEL.contains("google_sdk") ||
+        Build.MODEL.lowercase().contains("droid4x") ||
+        Build.MODEL.contains("Emulator") ||
+        Build.MODEL.contains("Android SDK built for x86") ||
+        Build.MANUFACTURER.contains("Genymotion") ||
+        (Build.BRAND.startsWith("generic") && Build.DEVICE.startsWith("generic")) ||
+        "google_sdk" == Build.PRODUCT ||
+        Build.HARDWARE.contains("goldfish") ||
+        Build.HARDWARE.contains("ranchu") ||
+        Build.HARDWARE.contains("vbox86") ||
+        Build.HARDWARE.contains("nox") ||
+        Build.HARDWARE.contains("cuttlefish")

amethyst/src/main/java/com/vitorpamplona/amethyst/service/okhttp/OkHttpClientFactory.kt

@@ -24,10 +24,13 @@ import com.vitorpamplona.amethyst.service.okhttp.OkHttpClientFactoryForRelays.Co
 import com.vitorpamplona.amethyst.service.okhttp.OkHttpClientFactoryForRelays.Companion.DEFAULT_SOCKS_PORT
 import com.vitorpamplona.amethyst.service.okhttp.OkHttpClientFactoryForRelays.Companion.DEFAULT_TIMEOUT_ON_MOBILE_SECS
 import com.vitorpamplona.amethyst.service.okhttp.OkHttpClientFactoryForRelays.Companion.DEFAULT_TIMEOUT_ON_WIFI_SECS
+import okhttp3.ConnectionPool
+import okhttp3.Dispatcher
 import okhttp3.OkHttpClient
 import java.net.InetSocketAddress
 import java.net.Proxy
 import java.time.Duration
+import java.util.concurrent.TimeUnit
 
 class OkHttpClientFactory(
     keyCache: EncryptionKeyCache,
@@ -36,9 +39,30 @@ class OkHttpClientFactory(
     // val logging = LoggingInterceptor()
     val keyDecryptor = EncryptedBlobInterceptor(keyCache)
 
+    // Most images/videos in a feed come from a small set of hosts (e.g. a single
+    // Blossom/imgproxy server). OkHttp's default dispatcher caps inflight requests
+    // per host at 5, which serializes feed loading. Raise the limits so the feed
+    // can parallelize downloads the way a browser does.
+    private val dispatcher =
+        Dispatcher().apply {
+            if (!isEmulator()) {
+                maxRequestsPerHost = 16
+                maxRequests = 128
+            } else {
+                maxRequestsPerHost = 5
+                maxRequests = 64
+            }
+        }
+
+    // Keep more HTTP/2 connections warm so scrolling doesn't repeatedly re-TLS
+    // to the same media host.
+    private val connectionPool = ConnectionPool(32, 5, TimeUnit.MINUTES)
+
     private val rootClient =
         OkHttpClient
             .Builder()
+            .dispatcher(dispatcher)
+            .connectionPool(connectionPool)
             .followRedirects(true)
             .followSslRedirects(true)
             .addInterceptor(DefaultContentTypeInterceptor(userAgent))

amethyst/src/main/java/com/vitorpamplona/amethyst/service/okhttp/OkHttpClientFactoryForRelays.kt

@@ -20,7 +20,6 @@
  */
 package com.vitorpamplona.amethyst.service.okhttp
 
-import android.os.Build
 import com.vitorpamplona.quartz.utils.Log
 import okhttp3.Dispatcher
 import okhttp3.OkHttpClient
@@ -38,22 +37,6 @@ class OkHttpClientFactoryForRelays(
         const val DEFAULT_TIMEOUT_ON_WIFI_SECS: Int = 10
         const val DEFAULT_TIMEOUT_ON_MOBILE_SECS: Int = 30
         const val WEBSOCKET_PING_INTERVAL_SECS: Long = 120
-
-        private fun isEmulator(): Boolean =
-            Build.FINGERPRINT.startsWith("generic") ||
-                Build.FINGERPRINT.lowercase().contains("emulator") ||
-                Build.MODEL.contains("google_sdk") ||
-                Build.MODEL.lowercase().contains("droid4x") ||
-                Build.MODEL.contains("Emulator") ||
-                Build.MODEL.contains("Android SDK built for x86") ||
-                Build.MANUFACTURER.contains("Genymotion") ||
-                (Build.BRAND.startsWith("generic") && Build.DEVICE.startsWith("generic")) ||
-                "google_sdk" == Build.PRODUCT ||
-                Build.HARDWARE.contains("goldfish") ||
-                Build.HARDWARE.contains("ranchu") ||
-                Build.HARDWARE.contains("vbox86") ||
-                Build.HARDWARE.contains("nox") ||
-                Build.HARDWARE.contains("cuttlefish")
     }
 
     val myDispatcher =