Add article history by SKU and SSE update signals for live clients.

Expose getHistoryBySku as GET /article/:sku/history, and document mutation-emitted company signals via GET /events.

src/api/sse.js

@@ -0,0 +1,52 @@
+/**
+ * In-process SSE hub. Clients subscribe via GET /events; handlers call emit()
+ * after a successful mutation so other tabs/users can refetch.
+ */
+
+/** @typedef {{ res: import('express').Response, companyId: number, userId: number }} SseClient */
+
+/** @type {Set<SseClient>} */
+const clients = new Set();
+
+const KEEP_ALIVE_MS = 25_000;
+
+/**
+ * Register an open SSE response. Caller must write the initial headers.
+ * @param {import('express').Response} res
+ * @param {{ companyId: number, userId: number }} meta
+ * @returns {() => void} unsubscribe
+ */
+export function subscribe(res, { companyId, userId }) {
+    /** @type {SseClient} */
+    const client = { res, companyId, userId };
+    clients.add(client);
+
+    const keepAlive = setInterval(() => {
+        if (res.writableEnded) return;
+        res.write(': keepalive\n\n');
+    }, KEEP_ALIVE_MS);
+
+    const unsubscribe = () => {
+        clearInterval(keepAlive);
+        clients.delete(client);
+    };
+
+    res.on('close', unsubscribe);
+    return unsubscribe;
+}
+
+/**
+ * Broadcast a named signal to subscribers of the given company.
+ * @param {string} signal - SSE event name (e.g. `category`)
+ * @param {{ companyId: number }} options
+ */
+export function emit(signal, { companyId }) {
+    if (companyId == null) return;
+
+    const frame = `event: ${signal}\ndata: {}\n\n`;
+    for (const client of clients) {
+        if (client.companyId !== companyId) continue;
+        if (client.res.writableEnded) continue;
+        client.res.write(frame);
+    }
+}