feat: agents connect by WebSocket, falling back to long polling and trying again each minute; auto, ws or lp per machine (0.1.0)

deploy/nginx.conf.example

@@ -4,14 +4,21 @@
 # Put this in /etc/nginx/sites-available/lp_agent and symlink it into
 # sites-enabled, then:  sudo nginx -t && sudo systemctl reload nginx
 #
-# Everything (agent + browser terminal) is plain HTTP long-polling, so NO
-# WebSocket config is needed. The two settings that matter:
-#   - proxy_buffering off      -> deliver long-poll responses immediately
-#   - proxy_read_timeout 120s  -> longer than the 25s long-poll hold
+# Agents connect by WebSocket (from 0.1.0), with HTTP long polling to fall
+# back on; the browser uses plain HTTP. The settings that matter:
+#   - Upgrade / Connection headers -> let the agents' WebSocket through
+#   - proxy_buffering off          -> deliver long-poll responses immediately
+#   - proxy_read_timeout 300s      -> longer than the 25s long-poll hold
 #
 # NOTE: proxy_pass MUST start with "http://". A bare "proxy_pass 127.0.0.1:8091;"
 # causes nginx error:  [emerg] invalid URL prefix.
 
+# "Connection: upgrade" for a WebSocket, "close" for everything else.
+map $http_upgrade $connection_upgrade {
+    default upgrade;
+    ''      close;
+}
+
 server {
     listen 8445 ssl;
     server_name REDACTED;
@@ -33,6 +40,9 @@ server {
         proxy_set_header X-Real-IP         $remote_addr;
         proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
+        # Agents' WebSocket.
+        proxy_set_header Upgrade           $http_upgrade;
+        proxy_set_header Connection        $connection_upgrade;
 
         # Long-poll behaviour: no buffering, generous read timeout.
         proxy_buffering     off;