Don't crash the agent if prismarine-viewer can't bind its port

mineflayerViewer() creates an http server on 3000+count_id but doesn't expose
it, so EADDRINUSE (e.g. something already on :3000, or two agents racing)
becomes an uncaught exception that kills the agent process. Probe the port
first and fall back to a warning + no viewer.

Author: domdomegg

src/agent/vision/browser_viewer.js

@@ -1,8 +1,31 @@
 import settings from '../settings.js';
+import http from 'http';
 import prismarineViewer from 'prismarine-viewer';
 const mineflayerViewer = prismarineViewer.mineflayer;
 
 export function addBrowserViewer(bot, count_id) {
-    if (settings.render_bot_view)
-        mineflayerViewer(bot, { port: 3000+count_id, firstPerson: true, });
-}
+    if (!settings.render_bot_view) return;
+    const port = 3000 + count_id;
+
+    const fail = (err) => {
+        console.warn(`prismarine-viewer failed on port ${port}: ${err.message}. Continuing without viewer.`);
+    };
+
+    // mineflayerViewer creates its own http server and never exposes it, so a
+    // listen failure (e.g. EADDRINUSE) surfaces as an unhandled 'error' event
+    // that kills the process. Hook createServer just long enough to attach an
+    // error listener to that server.
+    const origCreateServer = http.createServer;
+    http.createServer = (...args) => {
+        const server = origCreateServer(...args);
+        server.on('error', fail);
+        return server;
+    };
+    try {
+        mineflayerViewer(bot, { port, firstPerson: true });
+    } catch (err) {
+        fail(err);
+    } finally {
+        http.createServer = origCreateServer;
+    }
+}