fix(background): Wave 2 - fix interrupt status checks, display text, error recovery grace, LSP JSONC

- fix(background): include "interrupt" status in all terminal status checks (3 files)
- fix(background): display "INTERRUPTED" instead of "CANCELLED" for interrupted tasks
- fix(cli): add error recovery grace period in poll-for-completion
- fix(lsp): use JSONC parser for config loading to support comments

All changes verified with tests and typecheck.

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

@@ -0,0 +1,56 @@
+import { describe, test, expect, mock } from "bun:test"
+import type { BackgroundManager } from "../../features/background-agent"
+import { createBackgroundTask } from "./create-background-task"
+
+describe("createBackgroundTask", () => {
+  const mockManager = {
+    launch: mock(() => Promise.resolve({
+      id: "test-task-id",
+      sessionID: null,
+      description: "Test task",
+      agent: "test-agent",
+      status: "pending",
+    })),
+    getTask: mock(),
+  } as unknown as BackgroundManager
+
+  const tool = createBackgroundTask(mockManager)
+
+  const testContext = {
+    sessionID: "test-session",
+    messageID: "test-message",
+    agent: "test-agent",
+    abort: new AbortController().signal,
+  }
+
+  const testArgs = {
+    description: "Test background task",
+    prompt: "Test prompt",
+    agent: "test-agent",
+  }
+
+  test("detects interrupted task as failure", async () => {
+    //#given
+    mockManager.launch.mockResolvedValueOnce({
+      id: "test-task-id",
+      sessionID: null,
+      description: "Test task",
+      agent: "test-agent",
+      status: "pending",
+    })
+    mockManager.getTask.mockReturnValueOnce({
+      id: "test-task-id",
+      sessionID: null,
+      description: "Test task",
+      agent: "test-agent",
+      status: "interrupt",
+    })
+
+    //#when
+    const result = await tool.execute(testArgs, testContext)
+
+    //#then
+    expect(result).toContain("Task entered error state")
+    expect(result).toContain("test-task-id")
+  })
+})