feat(import): durable batch checkpoint and transient auto-retry

Mirror interactive batch runs into the import-job store so interrupted imports (restart, time-out, disconnect) can be resumed from Import History. Items are checkpointed as they settle (coalesced, serialized saves) and the mirror starts 'running' so the boot-time worker marks it 'interrupted' instead of double-importing; done items are never re-imported. Add bounded backoff retry for transient download/connection failures before marking an item failed, and point the client's time-out/network toasts at Import History.

src/lib/services/import/transient-retry.test.ts

@@ -0,0 +1,91 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+	isTransientImportError,
+	withTransientImportRetry,
+} from "./transient-retry";
+
+beforeEach(() => {
+	vi.useFakeTimers();
+});
+afterEach(() => {
+	vi.useRealTimers();
+});
+
+describe("isTransientImportError", () => {
+	it("flags connection and timeout classes", () => {
+		for (const message of [
+			"fetch failed",
+			"network error during download",
+			"service unavailable",
+			"HTTP 503",
+			"HTTP 500",
+			"Empty or truncated response",
+			"connection timed out",
+			"ECONNRESET",
+		]) {
+			expect(isTransientImportError(message)).toBe(true);
+		}
+	});
+
+	it("does not flag data errors or aborts", () => {
+		for (const message of [
+			undefined,
+			"Response is not a SWF file",
+			"Invalid Nitro bundle",
+			"This operation was aborted",
+			"classname missing in assets",
+			"HTTP 404",
+		]) {
+			expect(isTransientImportError(message)).toBe(false);
+		}
+	});
+});
+
+describe("withTransientImportRetry", () => {
+	it("returns success on the first attempt", async () => {
+		const attempt = vi.fn(async () => ({ ok: true as const, itemId: 1 }));
+		await expect(withTransientImportRetry(attempt)).resolves.toEqual({
+			ok: true,
+			itemId: 1,
+		});
+		expect(attempt).toHaveBeenCalledTimes(1);
+	});
+
+	it("retries transient failures until success", async () => {
+		const attempt = vi
+			.fn()
+			.mockResolvedValueOnce({ ok: false as const, error: "fetch failed" })
+			.mockResolvedValueOnce({ ok: false as const, error: "HTTP 503" })
+			.mockResolvedValueOnce({ ok: true as const, itemId: 7 });
+		const pending = withTransientImportRetry(attempt, 2);
+		await vi.advanceTimersByTimeAsync(2000);
+		await expect(pending).resolves.toEqual({ ok: true, itemId: 7 });
+		expect(attempt).toHaveBeenCalledTimes(3);
+	});
+
+	it("returns the last error after exhausting retries", async () => {
+		const attempt = vi.fn(async () => ({
+			ok: false as const,
+			error: "fetch failed",
+		}));
+		const pending = withTransientImportRetry(attempt, 2);
+		await vi.advanceTimersByTimeAsync(2000);
+		await expect(pending).resolves.toEqual({
+			ok: false,
+			error: "fetch failed",
+		});
+		expect(attempt).toHaveBeenCalledTimes(3);
+	});
+
+	it("does not retry non-transient failures", async () => {
+		const attempt = vi.fn(async () => ({
+			ok: false as const,
+			error: "Invalid Nitro bundle",
+		}));
+		await expect(withTransientImportRetry(attempt)).resolves.toEqual({
+			ok: false,
+			error: "Invalid Nitro bundle",
+		});
+		expect(attempt).toHaveBeenCalledTimes(1);
+	});
+});