@@ -8,7 +8,7 @@
     <ID>ComplexMethod:ConfigModelStoreListener.kt$ConfigModelStoreListener$private fun fetchParams()</ID>
     <ID>ComplexMethod:HttpClient.kt$HttpClient$private suspend fun makeRequestIODispatcher( url: String, method: String?, jsonBody: JSONObject?, timeout: Int, headers: OptionalHeaders?, ): HttpResponse</ID>
     <ID>ComplexMethod:IdentityOperationExecutor.kt$IdentityOperationExecutor$override suspend fun execute(operations: List&lt;Operation>): ExecutionResponse</ID>
-    <ID>ComplexMethod:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, ): ExecutionResponse</ID>
+    <ID>ComplexMethod:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, mergeIntoOnesignalId: String? = null, ): ExecutionResponse</ID>
     <ID>ComplexMethod:OSDatabase.kt$OSDatabase$@Synchronized private fun internalOnUpgrade( db: SQLiteDatabase, oldVersion: Int, newVersion: Int, )</ID>
     <ID>ComplexMethod:OperationModelStore.kt$OperationModelStore$override fun create(jsonObject: JSONObject?): Operation?</ID>
     <ID>ComplexMethod:OperationRepo.kt$OperationRepo$internal suspend fun executeOperations(ops: List&lt;OperationQueueItem>)</ID>
@@ -194,7 +194,7 @@
     <ID>LongMethod:FeatureFlagsBackendService.kt$FeatureFlagsBackendService$override suspend fun fetchRemoteFeatureFlags(appId: String): RemoteFeatureFlagsFetchOutcome</ID>
     <ID>LongMethod:HttpClient.kt$HttpClient$private suspend fun makeRequestIODispatcher( url: String, method: String?, jsonBody: JSONObject?, timeout: Int, headers: OptionalHeaders?, ): HttpResponse</ID>
     <ID>LongMethod:IdentityOperationExecutor.kt$IdentityOperationExecutor$override suspend fun execute(operations: List&lt;Operation>): ExecutionResponse</ID>
-    <ID>LongMethod:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, ): ExecutionResponse</ID>
+    <ID>LongMethod:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, mergeIntoOnesignalId: String? = null, ): ExecutionResponse</ID>
     <ID>LongMethod:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun loginUser( loginUserOp: LoginUserOperation, operations: List&lt;Operation>, ): ExecutionResponse</ID>
     <ID>LongMethod:OperationRepo.kt$OperationRepo$internal suspend fun executeOperations(ops: List&lt;OperationQueueItem>)</ID>
     <ID>LongMethod:OperationRepo.kt$OperationRepo$private fun internalEnqueue( queueItem: OperationQueueItem, flush: Boolean, addToStore: Boolean, index: Int? = null, )</ID>
@@ -293,7 +293,7 @@
     <ID>NestedBlockDepth:IdentityOperationExecutor.kt$IdentityOperationExecutor$override suspend fun execute(operations: List&lt;Operation>): ExecutionResponse</ID>
     <ID>NestedBlockDepth:InfluenceManager.kt$InfluenceManager$private fun attemptSessionUpgrade( entryAction: AppEntryAction, directId: String? = null, )</ID>
     <ID>NestedBlockDepth:JSONUtils.kt$JSONUtils$fun compareJSONArrays( jsonArray1: JSONArray?, jsonArray2: JSONArray?, ): Boolean</ID>
-    <ID>NestedBlockDepth:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, ): ExecutionResponse</ID>
+    <ID>NestedBlockDepth:LoginUserOperationExecutor.kt$LoginUserOperationExecutor$private suspend fun createUser( createUserOperation: LoginUserOperation, operations: List&lt;Operation>, mergeIntoOnesignalId: String? = null, ): ExecutionResponse</ID>
     <ID>NestedBlockDepth:RefreshUserOperationExecutor.kt$RefreshUserOperationExecutor$private suspend fun getUser(op: RefreshUserOperation): ExecutionResponse</ID>
     <ID>NestedBlockDepth:ServiceRegistration.kt$ServiceRegistrationReflection$override fun resolve(provider: IServiceProvider): Any?</ID>
     <ID>NestedBlockDepth:ServiceRegistration.kt$ServiceRegistrationReflection$private fun doesHaveAllParameters( constructor: Constructor&lt;*>, provider: IServiceProvider, ): Boolean</ID>
 
@@ -1,6 +1,7 @@
 package com.onesignal.user.internal.operations.impl.executors
 
 import android.os.Build
+import com.onesignal.OneSignalError
 import com.onesignal.common.AndroidUtils
 import com.onesignal.common.DeviceUtils
 import com.onesignal.common.IDManager
@@ -91,15 +92,12 @@ internal class LoginUserOperationExecutor(
             return ExecutionResponse(ExecutionResult.FAIL_NORETRY)
         }
         if (shouldCreateUserDirectly(loginUserOp, alias)) {
-            // When there is no existing user to attempt to associate with the externalId provided, we go right to
-            // createUser.  If there is no externalId provided this is an insert, if there is this will be an
-            // "upsert with retrieval" as the user may already exist.
-            //
-            // Under IV, also skip the optimistic SetAliasOperation: that inline op identifies the
-            // target user by `onesignal_id = existingOnesignalId`, but IV's alias-resolution would
-            // rewrite the call to identify by the new (not-yet-registered) `external_id`, producing
-            // a 404 or idempotent success against the wrong user. createUser's identities-map path
-            // handles the merge correctly through backend upsert semantics.
+            // A server anonymous user is merged by sending its onesignal_id. Under IV, skip
+            // SetAlias: alias resolution would target the new external_id and 404 or hit the wrong user.
+            anonymousUserToMerge(loginUserOp, alias)?.let { anonymousId ->
+                val merged = createUser(loginUserOp, operations, anonymousId)
+                if (!shouldAbandonMerge(merged)) return merged
+            }
             return createUser(loginUserOp, operations)
         } else {
             // before we create a user we attempt to associate the user defined by existingOnesignalId with the
@@ -179,8 +177,10 @@ internal class LoginUserOperationExecutor(
     private suspend fun createUser(
         createUserOperation: LoginUserOperation,
         operations: List<Operation>,
+        mergeIntoOnesignalId: String? = null,
     ): ExecutionResponse {
         val identities = mutableMapOf<String, String>()
+        mergeIntoOnesignalId?.let { identities[IdentityConstants.ONESIGNAL_ID] = it }
         var subscriptions = mapOf<String, SubscriptionObject>()
         val properties =
             PropertiesObject(
@@ -314,17 +314,29 @@ internal class LoginUserOperationExecutor(
                 metadata = LoginWaitMetadata(backendOneSignalId, emailSubscriptionId, smsSubscriptionId),
             )
         } catch (ex: BackendException) {
-            Logging.error("LoginUserOperationExecutor.createUser failed: HTTP ${ex.statusCode}")
             val responseType = NetworkUtils.getResponseStatusType(ex.statusCode)
-
-            return when (responseType) {
-                NetworkUtils.ResponseStatusType.RETRYABLE ->
-                    backendExecutionResponse(ExecutionResult.FAIL_RETRY, ex)
-                NetworkUtils.ResponseStatusType.UNAUTHORIZED ->
-                    backendExecutionResponse(ExecutionResult.FAIL_UNAUTHORIZED, ex)
-                else ->
-                    backendExecutionResponse(ExecutionResult.FAIL_NORETRY, ex)
+            val response =
+                when (responseType) {
+                    NetworkUtils.ResponseStatusType.RETRYABLE ->
+                        backendExecutionResponse(ExecutionResult.FAIL_RETRY, ex)
+                    NetworkUtils.ResponseStatusType.UNAUTHORIZED ->
+                        backendExecutionResponse(ExecutionResult.FAIL_UNAUTHORIZED, ex)
+                    else ->
+                        backendExecutionResponse(ExecutionResult.FAIL_NORETRY, ex)
+                }
+            // The caller retries an abandoned merge, so this failure is not the outcome.
+            if (mergeIntoOnesignalId != null && shouldAbandonMerge(response)) {
+                Logging.debug("LoginUserOperationExecutor merge attempt failed: HTTP ${ex.statusCode}")
+                if (responseType == NetworkUtils.ResponseStatusType.CONFLICT) {
+                    // Hardcode user-1. The 409 line above reads like a failure to the app.
+                    Logging.debug(
+                        "LoginUserOperationExecutor now handling 409 response with \"code\": \"user-1\" by switching to user with \"external_id\": \"${createUserOperation.externalId}\"",
+                    )
+                }
+            } else {
+                Logging.error("LoginUserOperationExecutor.createUser failed: HTTP ${ex.statusCode}")
             }
+            return response
         }
     }
 
@@ -469,6 +481,37 @@ internal class LoginUserOperationExecutor(
         return op.existingOnesignalId == null || alias == null
     }
 
+    // A profile login sends the anonymous user's ID with the new external ID, so Create User attaches
+    // the external ID to that user instead of creating a new one, like the SetAlias path does.
+    private fun anonymousUserToMerge(op: LoginUserOperation, alias: String?): String? {
+        if (!op.hasProfileFields() || _identityVerificationService.ivBehaviorActive || alias == null) return null
+        return op.existingOnesignalId?.takeUnless { IDManager.isLocalId(it) }
+    }
+
+    // Drop the anonymous id only when it can be why Create User failed.
+    // A 400 is the payload, so a second request would fail the same way.
+    private fun shouldAbandonMerge(response: ExecutionResponse): Boolean {
+        if (response.result != ExecutionResult.FAIL_NORETRY) return false
+        val status = response.httpStatusCode?.let { NetworkUtils.getResponseStatusType(it) }
+        return status == NetworkUtils.ResponseStatusType.MISSING ||
+            (status == NetworkUtils.ResponseStatusType.CONFLICT && onesignalIdConflict(response.httpResponse) != false)
+    }
+
+    /** False when a parsed error does not name onesignal_id. Null when the body has none. */
+    private fun onesignalIdConflict(body: String?): Boolean? =
+        OneSignalError.fromBackendResponse(HTTP_CONFLICT, body)
+            .details
+            .filter { it.backendCode != null || conflictingAliases(it).isNotEmpty() }
+            .takeIf { it.isNotEmpty() }
+            ?.any { namesMergedUser(it) }
+
+    // user-1 is any alias clash. Retry only when conflicting_aliases names onesignal_id.
+    private fun namesMergedUser(detail: OneSignalError.Detail): Boolean =
+        conflictingAliases(detail).containsKey(IdentityConstants.ONESIGNAL_ID)
+
+    private fun conflictingAliases(detail: OneSignalError.Detail): Map<*, *> =
+        detail.meta?.get(CONFLICTING_ALIASES) as? Map<*, *> ?: emptyMap<String, Any?>()
+
     private fun backendExecutionResponse(
         result: ExecutionResult,
         ex: BackendException,
@@ -481,6 +524,8 @@ internal class LoginUserOperationExecutor(
 
     companion object {
         const val LOGIN_USER = "login-user"
+        private const val HTTP_CONFLICT = 409
+        private const val CONFLICTING_ALIASES = "conflicting_aliases"
     }
 }