Reapply "feat(core): optional mdns service (#6192)"

This reverts commit 505068d5a6.

packages/opencode/src/server/mdns.ts

@@ -0,0 +1,57 @@
+import { Log } from "@/util/log"
+import Bonjour from "bonjour-service"
+
+const log = Log.create({ service: "mdns" })
+
+export namespace MDNS {
+  let bonjour: Bonjour | undefined
+  let currentPort: number | undefined
+
+  export function publish(port: number, name = "opencode") {
+    if (currentPort === port) return
+    if (bonjour) unpublish()
+
+    try {
+      bonjour = new Bonjour()
+      const service = bonjour.publish({
+        name,
+        type: "http",
+        port,
+        txt: { path: "/" },
+      })
+
+      service.on("up", () => {
+        log.info("mDNS service published", { name, port })
+      })
+
+      service.on("error", (err) => {
+        log.error("mDNS service error", { error: err })
+      })
+
+      currentPort = port
+    } catch (err) {
+      log.error("mDNS publish failed", { error: err })
+      if (bonjour) {
+        try {
+          bonjour.destroy()
+        } catch {}
+      }
+      bonjour = undefined
+      currentPort = undefined
+    }
+  }
+
+  export function unpublish() {
+    if (bonjour) {
+      try {
+        bonjour.unpublishAll()
+        bonjour.destroy()
+      } catch (err) {
+        log.error("mDNS unpublish failed", { error: err })
+      }
+      bonjour = undefined
+      currentPort = undefined
+      log.info("mDNS service unpublished")
+    }
+  }
+}