feat: add structured backend logging

Collector failures, service-API errors, WS connection lifecycle, and
config reload/discovery events were previously invisible outside the
browser (or, for a few config/discovery cases, logged with an
inconsistent ad-hoc console.error). Add a small scoped logger
(lib/logger.ts, level via LOG_LEVEL) and wire it through server.ts,
the scheduler, service collector, config loader/effective store, and
the WS server so operators can see failures via `docker logs`.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/ws/server.ts

@@ -6,6 +6,9 @@ import { effectiveConfigStore } from "@/lib/config/effective";
 import { toPublicConfig } from "@/lib/config/public";
 import type { Config } from "@/lib/config/schema";
 import type { WidgetResult } from "@/lib/types/widget-result";
+import { createLogger } from "@/lib/logger";
+
+const log = createLogger("ws");
 
 type Envelope =
   | { topic: string; type: "result"; ts: number; data: WidgetResult }
@@ -22,6 +25,8 @@ export function attachWebSocketServer(httpServer: HttpServer): WebSocketServer {
   const wss = new WebSocketServer({ noServer: true });
   const subscriptions = new Map<string, Set<WebSocket>>();
   const allSockets = new Set<WebSocket>();
+  const connectionIds = new WeakMap<WebSocket, number>();
+  let nextConnectionId = 1;
 
   function subscribe(socket: WebSocket, widgetId: string): void {
     let set = subscriptions.get(widgetId);
@@ -46,12 +51,16 @@ export function attachWebSocketServer(httpServer: HttpServer): WebSocketServer {
   }
 
   wss.on("connection", (socket) => {
+    const connectionId = nextConnectionId++;
+    connectionIds.set(socket, connectionId);
     allSockets.add(socket);
+    log.info("client connected", { connectionId, clients: allSockets.size });
 
     try {
       const config = effectiveConfigStore.get();
       send(socket, { topic: "config", type: "config:update", ts: Date.now(), data: toPublicConfig(config) });
-    } catch {
+    } catch (err) {
+      log.debug("no valid config to send on connect", { connectionId, error: (err as Error).message });
       // no valid config loaded yet; client keeps its SSR-seeded config until one arrives
     }
 
@@ -59,18 +68,27 @@ export function attachWebSocketServer(httpServer: HttpServer): WebSocketServer {
       let message: { action?: string; widgetId?: string };
       try {
         message = JSON.parse(raw.toString());
-      } catch {
+      } catch (err) {
+        log.warn("received malformed message", { connectionId, error: (err as Error).message });
         return;
       }
       if (message.action === "subscribe" && typeof message.widgetId === "string") {
+        log.debug("client subscribed", { connectionId, widgetId: message.widgetId });
         subscribe(socket, message.widgetId);
       } else if (message.action === "unsubscribe" && typeof message.widgetId === "string") {
+        log.debug("client unsubscribed", { connectionId, widgetId: message.widgetId });
         unsubscribe(socket, message.widgetId);
       }
     });
 
-    socket.on("close", () => cleanupSocket(socket));
-    socket.on("error", () => cleanupSocket(socket));
+    socket.on("close", (code) => {
+      log.info("client disconnected", { connectionId, code, clients: allSockets.size - 1 });
+      cleanupSocket(socket);
+    });
+    socket.on("error", (err) => {
+      log.error("socket error", { connectionId, error: err.message });
+      cleanupSocket(socket);
+    });
   });
 
   collectorScheduler.onResult((widgetId, result) => {