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/features/background-agent/parent-session-notifier.test.ts

@@ -0,0 +1,39 @@
+declare const require: (name: string) => any
+const { describe, test, expect } = require("bun:test")
+import type { BackgroundTask } from "./types"
+import { buildBackgroundTaskNotificationText } from "./background-task-notification-template"
+
+describe("notifyParentSession", () => {
+  test("displays INTERRUPTED for interrupted tasks", () => {
+    // given
+    const task: BackgroundTask = {
+      id: "test-task",
+      parentSessionID: "parent-session",
+      parentMessageID: "parent-message",
+      description: "Test task",
+      prompt: "Test prompt",
+      agent: "test-agent",
+      status: "interrupt",
+      startedAt: new Date(),
+      completedAt: new Date(),
+    }
+    const duration = "1s"
+    const statusText = task.status === "completed" ? "COMPLETED" : task.status === "interrupt" ? "INTERRUPTED" : "CANCELLED"
+    const allComplete = false
+    const remainingCount = 1
+    const completedTasks: BackgroundTask[] = []
+
+    // when
+    const notification = buildBackgroundTaskNotificationText({
+      task,
+      duration,
+      statusText,
+      allComplete,
+      remainingCount,
+      completedTasks,
+    })
+
+    // then
+    expect(notification).toContain("INTERRUPTED")
+  })
+})

src/features/background-agent/parent-session-notifier.ts

@@ -36,7 +36,7 @@ export async function notifyParentSession(
   const allComplete = !pendingSet || pendingSet.size === 0
   const remainingCount = pendingSet?.size ?? 0
 
-  const statusText = task.status === "completed" ? "COMPLETED" : "CANCELLED"
+  const statusText = task.status === "completed" ? "COMPLETED" : task.status === "interrupt" ? "INTERRUPTED" : "CANCELLED"
 
   const completedTasks = allComplete
     ? Array.from(state.tasks.values()).filter(