refactor(tooling): [MOD-DEV-01] own dev server lifecycle and report port failures

scripts/library/reload.ts

@@ -0,0 +1,60 @@
+import type { ServerResponse } from 'node:http'
+
+export const reloadScript = `<script>(() => {
+  const source = new EventSource('/livereload');
+  let reloading = false;
+  const reload = () => { if (!reloading) { reloading = true; location.reload(); } };
+  source.onmessage = reload;
+  source.onerror = () => { source.onopen = reload; };
+  addEventListener('pagehide', () => source.close(), { once: true });
+})();</script>`
+
+export function createReloadChannel() {
+  const clients = new Set<ServerResponse>()
+  let heartbeat: ReturnType<typeof setInterval> | undefined
+  let closed = false
+  function stopHeartbeat() {
+    clearInterval(heartbeat)
+    heartbeat = undefined
+  }
+  return {
+    add(response: ServerResponse) {
+      if (closed) {
+        response.writeHead(503).end()
+        return
+      }
+      response.writeHead(200, {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache',
+        'Connection': 'keep-alive',
+      })
+      response.write('event: connected\ndata: ready\n\n')
+      clients.add(response)
+      response.once('close', () => {
+        clients.delete(response)
+        if (!clients.size)
+          stopHeartbeat()
+      })
+      if (!heartbeat) {
+        heartbeat = setInterval(() => {
+          for (const client of clients)
+            client.write('event: ping\ndata: waiting\n\n')
+        }, 30000)
+        heartbeat.unref()
+      }
+    },
+    reload() {
+      if (!closed) {
+        for (const client of clients)
+          client.write('data: reload\n\n')
+      }
+    },
+    close() {
+      closed = true
+      stopHeartbeat()
+      for (const client of clients)
+        client.end()
+      clients.clear()
+    },
+  }
+}