feat(#5): add network-data API with atomic JSON writes and rolling backups

src/routes/api/network-data/+server.ts

@@ -0,0 +1,91 @@
+import { json } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+
+import { validateNetworkData } from '$lib/data/networkSchema';
+import {
+	checkWritableState,
+	isWriteEnabled,
+	readNetworkFile,
+	writeNetworkFile
+} from '$lib/server/networkPersistence';
+
+function serializeValidationErrors(errors: Array<{ path: string; message: string }>) {
+	return errors.map((issue) => ({
+		path: issue.path,
+		message: issue.message
+	}));
+}
+
+export const GET: RequestHandler = async () => {
+	try {
+		const [{ data, source, updatedAt }, writable] = await Promise.all([
+			readNetworkFile(),
+			checkWritableState()
+		]);
+		const validation = validateNetworkData(data);
+		if (!validation.valid || !validation.data) {
+			return json(
+				{
+					error: 'Stored network data is invalid',
+					details: serializeValidationErrors(validation.errors)
+				},
+				{ status: 500 }
+			);
+		}
+
+		return json({
+			data: validation.data,
+			writable,
+			source,
+			updatedAt
+		});
+	} catch (error) {
+		const message =
+			error instanceof Error && error.message ? error.message : 'Failed to read network data file';
+		return json({ error: message }, { status: 500 });
+	}
+};
+
+export const PUT: RequestHandler = async ({ request }) => {
+	if (!isWriteEnabled()) {
+		return json(
+			{
+				error: 'Write API disabled. Unset NETWORK_READ_ONLY to enable persistence.'
+			},
+			{ status: 403 }
+		);
+	}
+
+	let payload: unknown;
+	try {
+		payload = await request.json();
+	} catch {
+		return json({ error: 'Request body must be valid JSON' }, { status: 400 });
+	}
+
+	const validation = validateNetworkData(payload);
+	if (!validation.valid || !validation.data) {
+		return json(
+			{
+				error: 'Network data validation failed',
+				details: serializeValidationErrors(validation.errors)
+			},
+			{ status: 400 }
+		);
+	}
+
+	try {
+		const metadata = await writeNetworkFile(validation.data);
+		const writable = await checkWritableState();
+		return json({
+			data: validation.data,
+			writable,
+			source: metadata.source,
+			updatedAt: metadata.updatedAt
+		});
+	} catch (error) {
+		const message =
+			error instanceof Error && error.message ? error.message : 'Failed to persist network data';
+		return json({ error: message }, { status: 500 });
+	}
+};