test(background-agent): cover abort timeout handling

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/background-agent/abort-with-timeout.test.ts

@@ -0,0 +1,57 @@
+import { afterAll, describe, expect, mock, test } from "bun:test"
+
+const logMock = mock(() => {})
+
+mock.module("../../shared", () => ({
+  log: logMock,
+}))
+
+import { abortWithTimeout } from "./abort-with-timeout"
+import type { OpencodeClient } from "./opencode-client"
+
+function createClient(abort: (...args: Array<unknown>) => Promise<unknown>): OpencodeClient {
+  return {
+    session: {
+      abort: abort as never,
+    },
+  } as never
+}
+
+describe("abortWithTimeout", () => {
+  afterAll(() => {
+    mock.restore()
+  })
+
+  test("#given abort resolves before timeout #when abortWithTimeout runs #then it returns true", async () => {
+    // given
+    const abort = mock(async () => ({}))
+
+    // when
+    const result = await abortWithTimeout(createClient(abort), "session-1", 10)
+
+    // then
+    expect(result).toBe(true)
+    expect(abort).toHaveBeenCalledWith({ path: { id: "session-1" } })
+    expect(logMock).not.toHaveBeenCalled()
+  })
+
+  test("#given abort hangs indefinitely #when abortWithTimeout runs #then it logs warning and continues", async () => {
+    // given
+    const abort = mock(() => new Promise<never>(() => {}))
+
+    // when
+    const result = await Promise.race([
+      abortWithTimeout(createClient(abort), "session-2", 1),
+      new Promise<never>((_, reject) => {
+        setTimeout(() => reject(new Error("abort timeout test exceeded wait budget")), 100)
+      }),
+    ])
+
+    // then
+    expect(result).toBe(false)
+    expect(logMock).toHaveBeenCalledWith(
+      "[background-agent] Session abort timed out; continuing cleanup:",
+      { sessionID: "session-2", timeoutMs: 1 },
+    )
+  })
+})