feat: weighted random routing + mode switching + EWMA smoothing + stale eviction

- Weighted random routing (math/rand/v2 per-goroutine ChaCha8)
- PUT /api/route/mode for runtime mode switch (best / weighted_random)
- EWMA score smoothing (configurable smoothing_factor, default 0.3)
- Periodic stale node eviction (5 min threshold, 60s interval)
- Non-blocking WS broadcast (per-client buffered channel + writePump)
- Background rate limiter cleanup goroutine
- In-memory trunk gateway cache (zero disk I/O in hot path)
- Configurable load_avg multiplier (default 50.0, backward compat)
- UI mode indicator + admin Switch button in dashboard
- 42 tests: weighted random, mode switching, EWMA, eviction, API integration

web/src/lib/api.ts

@@ -198,6 +198,7 @@ export interface BalancerInfo {
   route_total: number;
   route_fallbacks: number;
   uptime_sec: number;
+  balance_mode: string;
 }
 
 export function connectWebSocket(onMessage: (data: any) => void): WebSocket {
@@ -223,3 +224,12 @@ export function connectWebSocket(onMessage: (data: any) => void): WebSocket {
 
   return ws;
 }
+
+// --- Route mode ---
+
+export async function setBalanceMode(mode: 'best' | 'weighted_random') {
+  return request<{ mode: string }>('/route/mode', {
+    method: 'PUT',
+    body: JSON.stringify({ mode }),
+  });
+}

web/src/routes/+page.svelte

@@ -3,20 +3,36 @@
   import { goto } from '$app/navigation';
   import { onMount, onDestroy } from 'svelte';
   import {
-    getNodes, connectWebSocket, isAuthenticated,
+    getNodes, connectWebSocket, isAuthenticated, setBalanceMode,
     type NodeInfo, type BalancerInfo
   } from '$lib/api';
-  import { Activity, Phone, Zap, AlertTriangle, Wifi, Server, Plug, Globe, ArrowLeftRight, Network } from 'lucide-svelte';
+  import { Activity, Phone, Zap, AlertTriangle, Wifi, Server, Plug, Globe, ArrowLeftRight, Network, Shuffle } from 'lucide-svelte';
 
   let nodes: NodeInfo[] = [];
   let balancer: BalancerInfo | null = null;
   let ws: WebSocket | null = null;
   let error: string | null = null;
+  let setModeBusy = false;
 
   if (browser && !isAuthenticated()) {
     goto('/login');
   }
 
+  function getRole(): string | null {
+    if (!browser) return null;
+    const token = localStorage.getItem('token');
+    if (!token) return null;
+    try {
+      const payload = JSON.parse(atob(token.split('.')[1]));
+      return payload.role || null;
+    } catch {
+      return null;
+    }
+  }
+
+  let role = browser ? getRole() : null;
+  $: isAdmin = role === 'admin';
+
   onMount(() => {
     loadNodes();
     ws = connectWebSocket((msg) => {
@@ -40,6 +56,19 @@
     }
   }
 
+  async function toggleMode() {
+    if (!balancer || setModeBusy) return;
+    const newMode = balancer.balance_mode === 'weighted_random' ? 'best' : 'weighted_random';
+    setModeBusy = true;
+    try {
+      await setBalanceMode(newMode);
+    } catch (e: any) {
+      error = e.message;
+    } finally {
+      setModeBusy = false;
+    }
+  }
+
   function scoreColor(score: number): string {
     if (score >= 70) return 'text-green-600';
     if (score >= 40) return 'text-yellow-600';
@@ -145,6 +174,21 @@
         {/if}
       </span>
     {/if}
+    <span class="opacity-30">|</span>
+    <span class="flex items-center gap-1 ml-auto">
+      <Shuffle class="h-3 w-3" />
+      <span class="font-medium">{balancer.balance_mode === 'weighted_random' ? 'Weighted' : 'Best'}</span>
+      {#if isAdmin}
+        <button
+          on:click={toggleMode}
+          disabled={setModeBusy}
+          class="ml-1 px-2 py-0.5 text-[10px] border rounded hover:bg-secondary transition-colors disabled:opacity-50"
+          title="Переключить режим балансировки"
+        >
+          {setModeBusy ? '...' : 'Switch'}
+        </button>
+      {/if}
+    </span>
   </div>
 {/if}