diff --git a/src/features/background-agent/notification-builder.ts b/src/features/background-agent/notification-builder.ts
index e16d2b4e..66e9c5a8 100644
--- a/src/features/background-agent/notification-builder.ts
+++ b/src/features/background-agent/notification-builder.ts
@@ -8,7 +8,8 @@ export function buildBackgroundTaskNotificationText(args: {
   completedTasks: BackgroundTask[]
 }): string {
   const { task, duration, allComplete, remainingCount, completedTasks } = args
-  const statusText = task.status === "completed" ? "COMPLETED" : "CANCELLED"
+  const statusText =
+    task.status === "completed" ? "COMPLETED" : task.status === "error" ? "ERROR" : "CANCELLED"
   const errorInfo = task.error ? `\n**Error:** ${task.error}` : ""
 
   if (allComplete) {
diff --git a/src/features/background-agent/parent-session-notifier.ts b/src/features/background-agent/parent-session-notifier.ts
index 9d4c1ac0..2c2ff05a 100644
--- a/src/features/background-agent/parent-session-notifier.ts
+++ b/src/features/background-agent/parent-session-notifier.ts
@@ -13,7 +13,7 @@ export async function notifyParentSession(
 ): Promise<void> {
   const { client, state } = ctx
 
-  const duration = formatDuration(task.startedAt ?? new Date(), task.completedAt)
+  const duration = formatDuration(task.startedAt ?? task.completedAt ?? new Date(), task.completedAt)
   log("[background-agent] notifyParentSession called for task:", task.id)
 
   const toastManager = getTaskToastManager()
diff --git a/src/features/background-agent/poll-running-tasks.ts b/src/features/background-agent/poll-running-tasks.ts
index 688bba6f..6c5a4461 100644
--- a/src/features/background-agent/poll-running-tasks.ts
+++ b/src/features/background-agent/poll-running-tasks.ts
@@ -94,7 +94,10 @@ export async function pollRunningTasks(args: {
         continue
       }
 
-      const messages = asSessionMessages((messagesResult as { data?: unknown }).data)
+      const messagesPayload = Array.isArray(messagesResult)
+        ? messagesResult
+        : (messagesResult as { data?: unknown }).data
+      const messages = asSessionMessages(messagesPayload)
       const assistantMsgs = messages.filter((m) => m.info?.role === "assistant")
 
       let toolCalls = 0
diff --git a/src/features/background-agent/session-output-validator.ts b/src/features/background-agent/session-output-validator.ts
index 136bcc41..8e14a21c 100644
--- a/src/features/background-agent/session-output-validator.ts
+++ b/src/features/background-agent/session-output-validator.ts
@@ -55,7 +55,8 @@ export async function validateSessionHasOutput(
       path: { id: sessionID },
     })
 
-    const messagesRaw = "data" in response ? response.data : []
+    const messagesRaw =
+      isObject(response) && "data" in response ? (response as { data?: unknown }).data : response
     const messages = Array.isArray(messagesRaw) ? messagesRaw : []
 
     const hasAssistantOrToolMessage = messages.some((message) => {
diff --git a/src/features/background-agent/task-queries.ts b/src/features/background-agent/task-queries.ts
index d53c6f90..641f0e41 100644
--- a/src/features/background-agent/task-queries.ts
+++ b/src/features/background-agent/task-queries.ts
@@ -45,7 +45,7 @@ export function getRunningTasks(tasks: Iterable<BackgroundTask>): BackgroundTask
 }
 
 export function getCompletedTasks(tasks: Iterable<BackgroundTask>): BackgroundTask[] {
-  return Array.from(tasks).filter((t) => t.status !== "running")
+  return Array.from(tasks).filter((t) => t.status === "completed")
 }
 
 export function hasRunningTasks(tasks: Iterable<BackgroundTask>): boolean {
diff --git a/src/features/background-agent/task-resumer.ts b/src/features/background-agent/task-resumer.ts
index e09b1276..632081c3 100644
--- a/src/features/background-agent/task-resumer.ts
+++ b/src/features/background-agent/task-resumer.ts
@@ -48,7 +48,11 @@ export async function resumeBackgroundTask(args: {
     return existingTask
   }
 
-  const concurrencyKey = existingTask.concurrencyGroup ?? existingTask.agent
+  const concurrencyKey =
+    existingTask.concurrencyGroup ??
+    (existingTask.model
+      ? `${existingTask.model.providerID}/${existingTask.model.modelID}`
+      : existingTask.agent)
   await concurrencyManager.acquire(concurrencyKey)
   existingTask.concurrencyKey = concurrencyKey
   existingTask.concurrencyGroup = concurrencyKey