feat: implement togglable debug log streaming for server stdout/stderr and client console logs

- Created server/utils/logCapture.js to intercept and buffer server output, stripping ANSI escape codes.
- Created server/middleware/logStreamAuth.js enforcing subnet IP filtering (LOG_ALLOW_SUBNETS), Emby session cookie, Basic Auth fallback, and X-Webhook-Secret header bypass.
- Created server/routes/debug.js with SSE streams /api/debug/server-logs, /api/debug/client-logs and batched POST /api/debug/client-logs. Exposes public configuration status at /api/debug/status.
- Integrated log capture and mounted debug routes in server/app.js and server/index.js.
- Implemented client/src/utils/clientLogCapture.js in the frontend SPA to hook console log/warn/error and flush batched console events.
- Documented all endpoints in OpenAPI server/openapi.yaml, ARCHITECTURE.md, and README.md.
- Wrote route integration tests and frontend console capture tests, with full validation in swagger-coverage.

client/src/main.js

@@ -11,8 +11,12 @@ import { initThemeSwitcher } from './ui/theme.js';
 import { initTabs, goHome } from './ui/tabs.js';
 import { handleShowAllToggle } from './sse.js';
 import { loadAppVersion } from './api.js';
+import { initClientLogCapture } from './utils/clientLogCapture.js';
 
 document.addEventListener('DOMContentLoaded', () => {
+  // Initialize client console log capturing early
+  initClientLogCapture();
+
   // Login form
   const loginForm = document.getElementById('login-form');
   if (loginForm) {

client/src/utils/clientLogCapture.js

@@ -0,0 +1,137 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+
+const logQueue = [];
+const MAX_QUEUE_SIZE = 20;
+const FLUSH_INTERVAL_MS = 2000;
+
+// Original console functions
+const originalLog = console.log;
+const originalWarn = console.warn;
+const originalError = console.error;
+
+let isSending = false;
+let isInitialized = false;
+let flushInterval = null;
+
+function formatArgs(args) {
+  return args.map(arg => {
+    if (arg === null) return 'null';
+    if (arg === undefined) return 'undefined';
+    if (arg instanceof Error) {
+      return `${arg.name}: ${arg.message}\n${arg.stack || ''}`;
+    }
+    if (typeof arg === 'object') {
+      try {
+        return JSON.stringify(arg);
+      } catch {
+        return String(arg);
+      }
+    }
+    return String(arg);
+  }).join(' ');
+}
+
+function enqueue(level, args) {
+  const formattedMsg = formatArgs(args);
+
+  // Still write to the developer console!
+  if (level === 'info') originalLog.apply(console, args);
+  else if (level === 'warn') originalWarn.apply(console, args);
+  else if (level === 'error') originalError.apply(console, args);
+
+  // Guard against infinite loop during logs dispatching
+  if (isSending) return;
+
+  logQueue.push({
+    timestamp: new Date().toISOString(),
+    level,
+    message: formattedMsg
+  });
+
+  // Flush immediately if queue is full
+  if (logQueue.length >= MAX_QUEUE_SIZE) {
+    flushQueue();
+  }
+}
+
+async function flushQueue() {
+  if (logQueue.length === 0 || isSending) return;
+
+  isSending = true;
+  const batch = [...logQueue];
+  logQueue.length = 0;
+
+  try {
+    const response = await fetch('/api/debug/client-logs', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify(batch),
+      // keepalive allows request to survive page unload
+      keepalive: true
+    });
+
+    if (!response.ok) {
+      originalError.call(console, '[clientLogCapture] Ingestion server returned error status:', response.status);
+    }
+  } catch (err) {
+    originalError.call(console, '[clientLogCapture] Ingestion post request failed:', err.message);
+  } finally {
+    isSending = false;
+  }
+}
+
+// Perform a fast/unblocked payload flush using sendBeacon on page unload
+function flushOnUnload() {
+  if (logQueue.length === 0) return;
+
+  const batch = [...logQueue];
+  logQueue.length = 0;
+
+  try {
+    const blob = new Blob([JSON.stringify(batch)], { type: 'application/json' });
+    navigator.sendBeacon('/api/debug/client-logs', blob);
+  } catch (err) {
+    // sendBeacon failure, fallback to synchronous fetch with keepalive if available
+    try {
+      fetch('/api/debug/client-logs', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(batch),
+        keepalive: true
+      });
+    } catch {
+      // Ignore
+    }
+  }
+}
+
+export async function initClientLogCapture() {
+  if (isInitialized) return;
+
+  try {
+    // 1. Check if the server toggle for logging is active
+    const response = await fetch('/api/debug/status');
+    if (!response.ok) return;
+
+    const data = await response.json();
+    if (data && data.enabled === true) {
+      // 2. Override global console methods
+      console.log = (...args) => enqueue('info', args);
+      console.warn = (...args) => enqueue('warn', args);
+      console.error = (...args) => enqueue('error', args);
+
+      // 3. Set interval for batch updates
+      flushInterval = setInterval(flushQueue, FLUSH_INTERVAL_MS);
+
+      // 4. Setup beforeunload listener for clean flushing
+      window.addEventListener('beforeunload', flushOnUnload);
+
+      isInitialized = true;
+      console.log('[clientLogCapture] Browser console logging interceptor initialized successfully.');
+    }
+  } catch (err) {
+    originalError.call(console, '[clientLogCapture] Check failed to start interceptor:', err.message);
+  }
+}