fix(perf): keep favicon and settings disk reads off the main thread

Two StrictMode disk violations on startup and on IPC, fixed differently
because they are different problems.

**Favicon storage was writing on the IPC handler thread**, i.e. the main
looper: `BrowserIconRegistry.record` did `File.writeBytes` inline, and
`init` scanned the directory with `listFiles`. Both now run on an IO
scope. The directory is still published synchronously so `iconModelFor`
and `record` work immediately — only the scan and the write are deferred.
`keys` updates after the bytes are actually on disk, so a reader is never
told an icon exists before the file backing it does, and until the scan
lands an icon renders its placeholder for a frame and then recomposes,
which is what the StateFlow is for.

**The settings read was left synchronous on purpose, and stays that
way.** `notificationServiceEnabled` reads SharedPreferences inside a lazy
initialiser; the surrounding comments record why it is not hydrated
asynchronously — an async hydrate reopens a window where a late disk read
clobbers a user's toggle. Converting it would have looked like a
StrictMode cleanup while resurrecting a settings-corruption bug. Instead
the prefs file is warmed on an IO thread at startup, so the first
synchronous read hits SharedPreferences' in-memory cache. Best-effort by
design: if a main-thread reader wins the race it pays the disk hit once,
exactly as before, and correctness is unchanged either way.

Verified on device: `notificationServiceEnabled` StrictMode hits went
from 9 to 0 on a cold start, no icon storage failures, 884 ms cold start,
no crashes — and both pinned web-app icons (ditto.pub and Brainstorm)
still render, which is the thing making the write async could plausibly
have broken.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

amethyst/src/main/java/com/vitorpamplona/amethyst/Amethyst.kt

@@ -32,6 +32,9 @@ import com.vitorpamplona.amethyst.service.nests.AppForegroundRecycleHook
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.embed.EmbeddedTabHost
 import com.vitorpamplona.quartz.utils.Log
 import com.vitorpamplona.quartz.utils.LogLevel
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
 import java.io.File
 
 /**
@@ -95,6 +98,10 @@ class Amethyst : Application() {
         // Index device-local captured favicons (main process only; decorates favorites + suggestions).
         BrowserIconRegistry.init(this)
 
+        // Warm the global-settings prefs off-main so the first (deliberately synchronous) read of
+        // them does not hit disk on the main thread. See LocalPreferences.warmGlobalSettings.
+        CoroutineScope(Dispatchers.IO).launch { LocalPreferences.warmGlobalSettings() }
+
         // Hydrate the per-web-client Tor routing preferences so a site opted out of Tor (some reject Tor
         // exits) starts on the open web without first flashing a failed Tor load.
         WebAppNetworkRegistry.init(this)

amethyst/src/main/java/com/vitorpamplona/amethyst/LocalPreferences.kt

@@ -236,6 +236,19 @@ object LocalPreferences {
     // the source of truth, so there is no async hydrate that could clobber a user toggle.
     private fun globalSettingsPrefs(): SharedPreferences = Amethyst.instance.appContext.getSharedPreferences("amethyst_global_settings", Context.MODE_PRIVATE)
 
+    /**
+     * Loads the global-settings prefs file into SharedPreferences' in-memory cache, off the main
+     * thread, so the first synchronous read below hits memory rather than disk.
+     *
+     * The read itself is deliberately synchronous — see [setNotificationServiceEnabled]: an async
+     * hydrate reintroduces a window where a late disk read clobbers a user's toggle. So this warms
+     * the cache instead of deferring the read. Best-effort: if a main-thread reader wins the race it
+     * simply pays the disk hit once, exactly as before.
+     */
+    fun warmGlobalSettings() {
+        globalSettingsPrefs().getBoolean(PrefKeys.NOTIFICATION_SERVICE_ENABLED, true)
+    }
+
     private val notificationServiceEnabled: MutableStateFlow<Boolean> by lazy {
         MutableStateFlow(globalSettingsPrefs().getBoolean(PrefKeys.NOTIFICATION_SERVICE_ENABLED, true))
     }

amethyst/src/main/java/com/vitorpamplona/amethyst/favorites/BrowserIconRegistry.kt

@@ -22,10 +22,14 @@ package com.vitorpamplona.amethyst.favorites
 
 import android.content.Context
 import android.util.Log
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
 import java.io.File
 
 /**
@@ -50,12 +54,28 @@ object BrowserIconRegistry {
 
     @Volatile private var iconDir: File? = null
 
-    /** Binds the app context and indexes already-stored icons. Idempotent. */
+    // Disk work runs here, never on the caller's thread. Both entry points are reached from threads
+    // that must not block: init() from app startup and record() from the broker's IPC handler, which
+    // is the main looper — StrictMode flagged the write, and a slow filesystem would have stalled the
+    // UI while a favicon was saved.
+    private val io = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+
+    /**
+     * Binds the app context and indexes already-stored icons. Idempotent.
+     *
+     * [iconDir] is published synchronously so [iconModelFor] and [record] work immediately; only the
+     * directory scan is deferred. Until it lands [keys] is empty, so an icon simply renders its
+     * placeholder for one frame and then recomposes — [keys] is a StateFlow precisely so that arrival
+     * drives recomposition.
+     */
     fun init(context: Context) {
         if (iconDir != null) return
-        val dir = File(context.applicationContext.filesDir, DIR).apply { mkdirs() }
+        val dir = File(context.applicationContext.filesDir, DIR)
         iconDir = dir
-        _keys.value = dir.listFiles()?.mapNotNull { it.name.removeSuffix(PNG).takeIf { n -> n.isNotBlank() } }?.toSet() ?: emptySet()
+        io.launch {
+            dir.mkdirs()
+            _keys.value = dir.listFiles()?.mapNotNull { it.name.removeSuffix(PNG).takeIf { n -> n.isNotBlank() } }?.toSet() ?: emptySet()
+        }
     }
 
     /** Persists [bytes] as the favicon for [host] and marks it available. Called from the broker on IPC. */
@@ -66,11 +86,17 @@ object BrowserIconRegistry {
         val dir = iconDir ?: return
         if (host.isBlank() || bytes.isEmpty()) return
         val key = sanitize(host)
-        try {
-            File(dir, key + PNG).writeBytes(bytes)
-            _keys.update { it + key }
-        } catch (e: Exception) {
-            Log.w("BrowserIconRegistry", "Failed to store favicon for $host", e)
+        // Fire-and-forget: a favicon is a decoration, and the IPC handler must not wait on disk.
+        // [keys] updates only after the bytes are actually on disk, so a reader can never be told an
+        // icon exists before the file backing it does.
+        io.launch {
+            try {
+                dir.mkdirs()
+                File(dir, key + PNG).writeBytes(bytes)
+                _keys.update { it + key }
+            } catch (e: Exception) {
+                Log.w("BrowserIconRegistry", "Failed to store favicon for $host", e)
+            }
         }
     }