From 2659180f2272a0aa976d4d4f7bb5342381792ba3 Mon Sep 17 00:00:00 2001
From: Brandon McAnsh <git@bmcreations.dev>
Date: Thu, 15 Oct 2026 08:55:10 -0400
Subject: [PATCH] fix(trace): set the Bugsnag user off the main thread

Account creation sets the trace user id on the main thread, and the
listener called Bugsnag.setUser there. That call waits on the NDK
plugin's state lock, which Bugsnag's worker can hold in
synchronizeState while it waits on calculateFreeDisk, so the UI froze
until the worker let go (Bugsnag 6acec70adbd69358a81f2824, 6acfc33f,
both on 4804).

User id changes now go to Bugsnag one at a time on a background
dispatcher, in the order they were made.
---
 .../app/internal/startup/ForwardUserId.kt     | 28 +++++++++++
 .../app/internal/startup/TraceInitializer.kt  |  4 +-
 .../app/internal/startup/ForwardUserIdTest.kt | 46 +++++++++++++++++++
 3 files changed, 75 insertions(+), 3 deletions(-)
 create mode 100644 apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/ForwardUserId.kt
 create mode 100644 apps/flipcash/app/src/test/kotlin/com/flipcash/app/internal/startup/ForwardUserIdTest.kt

diff --git a/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/ForwardUserId.kt b/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/ForwardUserId.kt
new file mode 100644
index 0000000000..d74409b99d
--- /dev/null
+++ b/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/ForwardUserId.kt
@@ -0,0 +1,28 @@
+package com.flipcash.app.internal.startup
+
+import com.bugsnag.android.Bugsnag
+import com.getcode.utils.TraceManager
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Dispatchers
+
+/**
+ * Forwards every [TraceManager.userId] change to [setUser] on [dispatcher], never on the thread
+ * that changed it.
+ *
+ * `Bugsnag.setUser` takes the NDK plugin's state lock, and Bugsnag's own worker holds that lock in
+ * `NativeBridge.synchronizeState` while it waits on `DeviceDataCollector.calculateFreeDisk`. Account
+ * creation sets the user id on the main thread, so calling Bugsnag there froze the UI until the
+ * worker let go — the ANR in Bugsnag `6acec70adbd69358a81f2824`.
+ *
+ * [dispatcher] runs one change at a time, in order, so a sign-out followed by a sign-in leaves
+ * Bugsnag with the signed-in id.
+ */
+@OptIn(kotlinx.coroutines.ExperimentalCoroutinesApi::class)
+internal fun forwardUserIdOffThread(
+    dispatcher: CoroutineDispatcher = Dispatchers.IO.limitedParallelism(1),
+    setUser: (String?) -> Unit = { id -> Bugsnag.setUser(id, null, null) },
+) {
+    TraceManager.setOnUserIdChanged { id ->
+        launchBestEffort(tag = "bugsnag-user", dispatcher = dispatcher) { setUser(id) }
+    }
+}
diff --git a/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/TraceInitializer.kt b/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/TraceInitializer.kt
index 10165c2cb1..57831c3500 100644
--- a/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/TraceInitializer.kt
+++ b/apps/flipcash/app/src/main/kotlin/com/flipcash/app/internal/startup/TraceInitializer.kt
@@ -57,9 +57,7 @@ class TraceInitializer: Initializer<Unit> {
 
                 ErrorUtils.addReporter(BugsnagErrorReporter())
                 TraceManager.addSink(BugsnagBreadcrumbSink())
-                TraceManager.setOnUserIdChanged { id ->
-                    Bugsnag.setUser(id, null, null)
-                }
+                forwardUserIdOffThread()
 
                 stageProvider.fetchAndCache(versionCode)
                 if (stageProvider.resolvedStage == ReleaseStage.Internal) {
diff --git a/apps/flipcash/app/src/test/kotlin/com/flipcash/app/internal/startup/ForwardUserIdTest.kt b/apps/flipcash/app/src/test/kotlin/com/flipcash/app/internal/startup/ForwardUserIdTest.kt
new file mode 100644
index 0000000000..93b979d00c
--- /dev/null
+++ b/apps/flipcash/app/src/test/kotlin/com/flipcash/app/internal/startup/ForwardUserIdTest.kt
@@ -0,0 +1,46 @@
+package com.flipcash.app.internal.startup
+
+import com.getcode.utils.TraceManager
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.runTest
+import kotlin.test.AfterTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class ForwardUserIdTest {
+
+    @AfterTest
+    fun tearDown() {
+        TraceManager.setOnUserIdChanged(null)
+        TraceManager.userId = null
+    }
+
+    @Test
+    fun `does not call setUser on the thread that changed the id`() = runTest {
+        val forwarded = mutableListOf<String?>()
+        forwardUserIdOffThread(dispatcher = StandardTestDispatcher(testScheduler)) { forwarded += it }
+
+        TraceManager.userId = "user-1"
+
+        assertTrue(forwarded.isEmpty())
+        advanceUntilIdle()
+        assertEquals(listOf<String?>("user-1"), forwarded)
+    }
+
+    @Test
+    fun `forwards changes in the order they were made`() = runTest {
+        val forwarded = mutableListOf<String?>()
+        forwardUserIdOffThread(dispatcher = StandardTestDispatcher(testScheduler)) { forwarded += it }
+
+        TraceManager.userId = "user-1"
+        TraceManager.userId = null
+        TraceManager.userId = "user-2"
+        advanceUntilIdle()
+
+        assertEquals(listOf("user-1", null, "user-2"), forwarded)
+    }
+}