perf(background-task): reduce output poll latency

src/tools/background-task/create-background-output.polling-interval.test.ts

@@ -0,0 +1,71 @@
+/// <reference types="bun-types" />
+import { describe, expect, test } from "bun:test"
+import type { BackgroundTask } from "../../features/background-agent"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
+import { createBackgroundOutput } from "./create-background-output"
+import type { BackgroundOutputClient, BackgroundOutputManager } from "./clients"
+
+const mockContext = unsafeTestValue<Parameters<ReturnType<typeof createBackgroundOutput>["execute"]>[1]>({
+  sessionID: "ses_parent",
+  messageID: "msg_parent",
+  agent: "sisyphus",
+  abort: new AbortController().signal,
+})
+
+function createTask(): BackgroundTask {
+  return {
+    id: "bg_fast_poll",
+    sessionId: "ses_fast_poll",
+    parentSessionId: "ses_parent",
+    parentMessageId: "msg_parent",
+    description: "fast poll",
+    prompt: "run",
+    agent: "sisyphus-junior",
+    status: "running",
+  }
+}
+
+const client: BackgroundOutputClient = {
+  session: {
+    messages: async () => ({
+      data: [
+        {
+          info: { role: "assistant", time: "2026-01-01T00:00:00Z" },
+          parts: [{ type: "text", text: "completed result" }],
+        },
+      ],
+    }),
+  },
+}
+
+describe("background_output blocking poll interval", () => {
+  test("#given a short blocking timeout and a task that completes on retry #when fetching output #then it does not sleep for the legacy one second interval", async () => {
+    // given
+    let pollCount = 0
+    const task = createTask()
+    const manager: BackgroundOutputManager = {
+      getTask: (id: string) => {
+        if (id !== task.id) return undefined
+        pollCount += 1
+        if (pollCount >= 3) {
+          task.status = "completed"
+        }
+        return task
+      },
+    }
+    const tool = createBackgroundOutput(manager, client)
+    const startedAt = Date.now()
+
+    // when
+    const output = await tool.execute({
+      task_id: task.id,
+      block: true,
+      timeout: 30,
+    }, mockContext)
+
+    // then
+    expect(Date.now() - startedAt).toBeLessThan(200)
+    expect(pollCount).toBeGreaterThanOrEqual(3)
+    expect(output).toContain("completed result")
+  })
+})

src/tools/background-task/create-background-output.ts

@@ -15,6 +15,7 @@ import { recordBackgroundOutputConsumption } from "../../shared/background-outpu
 
 const SISYPHUS_JUNIOR_AGENT = getAgentDisplayName("sisyphus-junior")
 const MISSING_BACKGROUND_TASK_RETRY_DELAY_MS = 100
+const BACKGROUND_OUTPUT_POLL_INTERVAL_MS = 100
 
 type ToolContextWithMetadata = {
   sessionID: string
@@ -140,7 +141,8 @@ export function createBackgroundOutput(manager: BackgroundOutputManager, client:
         if (shouldBlock && isTaskActiveStatus(task.status)) {
           const startTime = Date.now()
           while (Date.now() - startTime < timeoutMs) {
-            await delay(1000)
+            const remainingMs = timeoutMs - (Date.now() - startTime)
+            await delay(Math.min(BACKGROUND_OUTPUT_POLL_INTERVAL_MS, Math.max(1, remainingMs)))
 
             const currentTask = await getTaskWithMissingRetry(manager, args.task_id)
             if (!currentTask) {