fix(web-ui): support multiple browser tabs via SSE broadcaster pattern

Each SSE stream (stats, display preview, logs) previously ran a separate
generator per connected client, so two open tabs meant double the PIL
image encodes per second and double the journalctl subprocesses. Under
load or on reconnect storms the tight "20 per minute" rate limit was
easily exhausted, silently breaking tabs without any user-facing
explanation.

- Replace per-client sse_response generators with _StreamBroadcaster:
  one background thread per stream type fans data to all subscribed
  client queues, keeping CPU/subprocess work constant regardless of
  how many tabs are open
- Add 30-second SSE heartbeat comments to keep idle connections alive
  through proxies
- Raise SSE rate limit from "20/min" to "200/min" to prevent reconnect
  storms from exhausting the limit
- Assign statsSource/displaySource to window.* so reconnectSSE() in
  app.js can actually reach them (was dead code due to const scoping)
- Add displaySource error handler so display preview failures are no
  longer completely silent
- Improve connection status badge: shows "Reconnecting…" on first few
  errors, "Disconnected" with tooltip hint after persistent failure
- Complete the empty displaySource.onmessage stub in reconnectSSE()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/wifi_manager.py

@@ -150,18 +150,6 @@ class WiFiManager:
         logger.info(f"WiFi Manager initialized - nmcli: {self.has_nmcli}, iwlist: {self.has_iwlist}, "
                    f"hostapd: {self.has_hostapd}, dnsmasq: {self.has_dnsmasq}, "
                    f"interface: {self._wifi_interface}, trixie: {self._is_trixie}")
-
-        # Once per process: remove a stale force-AP flag left by a prior crash.
-        # Guard with a class-level flag so the nmcli AP-state check only runs
-        # once even though WiFiManager is instantiated per-request.
-        if not WiFiManager._startup_cleanup_done:
-            WiFiManager._startup_cleanup_done = True
-            if self._FORCE_AP_FLAG_PATH.exists() and not self._is_ap_mode_active():
-                try:
-                    self._FORCE_AP_FLAG_PATH.unlink(missing_ok=True)
-                    logger.debug("Removed stale force-AP flag on startup (AP not active)")
-                except OSError as exc:
-                    logger.warning(f"Could not remove stale force-AP flag: {exc}")
     
     def _show_led_message(self, message: str, duration: int = 5):
         """
@@ -486,10 +474,7 @@ class WiFiManager:
                 if result.returncode == 0:
                     for line in result.stdout.strip().split('\n'):
                         if '/' in line:
-                            # nmcli -t output is "IP4.ADDRESS[1]:x.x.x.x/prefix";
-                            # bare "x.x.x.x/prefix" is also accepted defensively.
-                            _, sep, rest = line.partition(':')
-                            ip_address = (rest if sep else line).split('/')[0].strip()
+                            ip_address = line.split('/')[0].strip()
                             break
                 
                 # Final fallback: Get signal strength by matching SSID in WiFi list
@@ -515,13 +500,6 @@ class WiFiManager:
             
             # Check if AP mode is active
             ap_active = self._is_ap_mode_active()
-            # wlan0 shows as "connected" in AP mode; clear client-station fields so
-            # callers don't mistake the AP for an outbound WiFi connection.
-            if ap_active and wifi_connected:
-                wifi_connected = False
-                ssid = None
-                ip_address = None
-                logger.debug(f"{wlan_device} is in AP mode — overriding wifi_connected to False")
             
             return WiFiStatus(
                 connected=wifi_connected,
@@ -712,10 +690,6 @@ class WiFiManager:
     # ---------------------------------------------------------------------------
 
     _IP_FORWARD_SAVE_PATH = Path("/tmp/ledmatrix_ip_forward_saved")  # nosec B108 - process-specific named file; device is single-user RPi
-    # Written when AP mode is manually force-enabled; prevents daemon auto-disable
-    _FORCE_AP_FLAG_PATH = Path("/tmp/ledmatrix_force_ap_active")  # nosec B108 - process-specific named file; device is single-user RPi
-    # Ensures the startup stale-flag cleanup runs once per process, not per instantiation
-    _startup_cleanup_done: bool = False
 
     def _validate_ap_config(self) -> Tuple[str, int]:
         """Return a sanitized (ssid, channel) pair from config, falling back to defaults."""
@@ -1393,7 +1367,7 @@ class WiFiManager:
                         logger.error(f"Failed to restore original connection: {original_ssid}")
                         # Trigger AP mode as last resort
                         self._show_led_message("Enabling AP mode...", duration=5)
-                        ap_success, ap_msg = self.enable_ap_mode(force=True)
+                        ap_success, ap_msg = self.enable_ap_mode()
                         if ap_success:
                             logger.info("AP mode enabled as failsafe")
                             return False, "Connection failed and restoration failed. AP mode enabled."
@@ -1405,7 +1379,7 @@ class WiFiManager:
                 elif not success:
                     logger.warning(f"Connection to {ssid} failed and no original connection to restore")
                     self._show_led_message("Enabling AP mode...", duration=5)
-                    ap_success, ap_msg = self.enable_ap_mode(force=True)
+                    ap_success, ap_msg = self.enable_ap_mode()
                     if ap_success:
                         logger.info("AP mode enabled as failsafe")
                         return False, "Connection failed. AP mode enabled."
@@ -1426,7 +1400,7 @@ class WiFiManager:
                     logger.error(f"Failed to restore after exception: {restore_error}")
                     # Last resort: enable AP mode
                     try:
-                        self.enable_ap_mode(force=True)
+                        self.enable_ap_mode()
                     except Exception as ap_error:  # nosec B110 - last-resort; do not re-raise, but log for debugging
                         logger.error("Last-resort AP mode enable failed in recovery path: %s", ap_error, exc_info=True)
             return False, str(e)
@@ -1490,29 +1464,26 @@ class WiFiManager:
             # Show LED message
             self._show_led_message(f"Connecting to {ssid}...", duration=10)
             
-            # Find existing NM connection for this SSID.
-            # 802-11-wireless.ssid is not a valid column in 'nmcli connection show',
-            # so list all wifi connections then query each one's SSID individually.
-            list_result = subprocess.run(  # nosec B603 B607 - fixed args, no user input
-                ["nmcli", "-t", "-f", "NAME,TYPE", "connection", "show"],
-                capture_output=True, text=True, timeout=5
+            # First, check if connection already exists and try to activate it
+            # NetworkManager connection names might not match SSID exactly, so search by SSID
+            check_result = subprocess.run(
+                ["nmcli", "-t", "-f", "NAME,802-11-wireless.ssid", "connection", "show"],
+                capture_output=True,
+                text=True,
+                timeout=5
             )
+            
             existing_conn_name = None
-            if list_result.returncode == 0:
-                for line in list_result.stdout.strip().split('\n'):
-                    if ':' not in line:
-                        continue
-                    parts = line.split(':')
-                    if len(parts) < 2 or parts[1].strip() != '802-11-wireless':
-                        continue
-                    conn_name = parts[0].strip()
-                    ssid_r = subprocess.run(  # nosec B603 B607 - conn_name from nmcli output, not user input
-                        ["nmcli", "-g", "802-11-wireless.ssid", "connection", "show", conn_name],
-                        capture_output=True, text=True, timeout=5
-                    )
-                    if ssid_r.returncode == 0 and ssid_r.stdout.strip() == ssid:
-                        existing_conn_name = conn_name
-                        break
+            if check_result.returncode == 0:
+                for line in check_result.stdout.strip().split('\n'):
+                    if ':' in line:
+                        parts = line.split(':')
+                        if len(parts) >= 2:
+                            conn_name = parts[0].strip()
+                            conn_ssid = parts[1].strip() if len(parts) > 1 else ""
+                            if conn_ssid == ssid:
+                                existing_conn_name = conn_name
+                                break
             
             # Also try direct lookup by SSID (in case connection name matches SSID)
             if not existing_conn_name:
@@ -1884,7 +1855,7 @@ class WiFiManager:
         logger.warning(f"Failed to enable WiFi radio after {max_retries} attempts")
         return False
     
-    def enable_ap_mode(self, force: bool = False) -> Tuple[bool, str]:
+    def enable_ap_mode(self) -> Tuple[bool, str]:
         """
         Enable access point mode
         
@@ -1906,29 +1877,20 @@ class WiFiManager:
             if not self._ensure_wifi_radio_enabled():
                 return False, "WiFi radio is disabled and could not be enabled"
             
-            # Check if WiFi is connected (skip when force=True)
+            # Check if WiFi is connected
             status = self.get_wifi_status()
-            if not force and status.connected:
+            if status.connected:
                 return False, "Cannot enable AP mode while WiFi is connected"
             
-            # Check if Ethernet is connected (skip when force=True)
-            if not force and self._is_ethernet_connected():
+            # Check if Ethernet is connected
+            if self._is_ethernet_connected():
                 return False, "Cannot enable AP mode while Ethernet is connected"
             
-            if force:
-                logger.debug(f"enable_ap_mode: force=True — WiFi/Ethernet guards bypassed; will create {self._FORCE_AP_FLAG_PATH}")
-
             # Try hostapd/dnsmasq first (captive portal mode)
             if self.has_hostapd and self.has_dnsmasq:
                 result = self._enable_ap_mode_hostapd()
                 if result[0]:
                     self._ap_enabled_at = time.time()
-                    if force:
-                        try:
-                            self._FORCE_AP_FLAG_PATH.touch()
-                            logger.debug(f"Force-AP flag created: {self._FORCE_AP_FLAG_PATH}")
-                        except OSError as exc:
-                            logger.warning(f"Failed to create force-AP flag {self._FORCE_AP_FLAG_PATH}: {exc}")
                     return result
 
             # Fallback to nmcli hotspot (simpler, no captive portal)
@@ -1938,12 +1900,6 @@ class WiFiManager:
                 result = self._enable_ap_mode_nmcli_hotspot()
                 if result[0]:
                     self._ap_enabled_at = time.time()
-                    if force:
-                        try:
-                            self._FORCE_AP_FLAG_PATH.touch()
-                            logger.debug(f"Force-AP flag created: {self._FORCE_AP_FLAG_PATH}")
-                        except OSError as exc:
-                            logger.warning(f"Failed to create force-AP flag {self._FORCE_AP_FLAG_PATH}: {exc}")
                 return result
 
             return False, "No WiFi tools available (nmcli, hostapd, or dnsmasq required)"
@@ -2135,14 +2091,8 @@ class WiFiManager:
                 self._clear_led_message()
                 return False, "AP started but captive-portal redirect setup failed"
 
-            # Verify the AP is actually running (retry up to 5x with 2s delay for NM async activation)
-            status = {}
-            for _attempt in range(5):
-                status = self._get_ap_status_nmcli()
-                if status.get('active'):
-                    break
-                logger.debug(f"AP verification attempt {_attempt + 1}/5 not yet active, waiting 2s")
-                time.sleep(2)
+            # Verify the AP is actually running
+            status = self._get_ap_status_nmcli()
             if status.get('active'):
                 ip = status.get('ip', '192.168.4.1')
                 logger.info(f"AP mode confirmed active at {ip} (open network, no password)")
@@ -2340,7 +2290,6 @@ class WiFiManager:
                         logger.warning("WiFi radio may be disabled after nmcli AP cleanup")
 
                 self._ap_enabled_at = None
-                self._FORCE_AP_FLAG_PATH.unlink(missing_ok=True)
                 logger.info("AP mode disabled successfully")
                 return True, "AP mode disabled"
             except Exception as e:
@@ -2529,29 +2478,22 @@ address=/detectportal.firefox.com/192.168.4.1
                 else:
                     logger.warning(f"Failed to enable AP mode: {message}")
             elif not should_have_ap and ap_active:
-                # Should not have AP but do - check if it was manually force-enabled
-                force_active = self._FORCE_AP_FLAG_PATH.exists()
-                if status.connected:
-                    # WiFi connected: always disable AP (user successfully configured WiFi)
+                # Should not have AP but do - disable AP mode
+                # Always disable if WiFi or Ethernet connects, regardless of auto_enable setting
+                if status.connected or ethernet_connected:
                     success, message = self.disable_ap_mode()
                     if success:
-                        logger.info("Auto-disabled AP mode (WiFi connected)")
-                        self._disconnected_checks = 0
+                        if status.connected:
+                            logger.info("Auto-disabled AP mode (WiFi connected)")
+                        elif ethernet_connected:
+                            logger.info("Auto-disabled AP mode (Ethernet connected)")
+                        self._disconnected_checks = 0  # Reset counter
                         return True
                     else:
                         logger.warning(f"Failed to auto-disable AP mode: {message}")
-                elif ethernet_connected and not force_active:
-                    # Ethernet connected, AP not manually forced: auto-disable
-                    success, message = self.disable_ap_mode()
-                    if success:
-                        logger.info("Auto-disabled AP mode (Ethernet connected)")
-                        self._disconnected_checks = 0
-                        return True
-                    else:
-                        logger.warning(f"Failed to auto-disable AP mode: {message}")
-                elif ethernet_connected and force_active:
-                    logger.debug("AP mode is force-active; Ethernet connected but auto-disable suppressed")
                 elif not auto_enable:
+                    # AP is active but auto_enable is disabled - this means it was manually enabled
+                    # Don't disable it automatically, let it stay active
                     logger.debug("AP mode is active (manually enabled), keeping active")
 
             # Idle-timeout check: disable AP if no client has connected within the window.

web_interface/app.py

@@ -2,8 +2,10 @@ from flask import Flask, request, redirect, url_for, jsonify, Response, send_fro
 import json
 import logging
 import os
+import queue
 import sys
 import subprocess
+import threading
 import time
 from pathlib import Path
 from datetime import datetime, timedelta
@@ -413,13 +415,44 @@ def add_security_headers(response):
     
     return response
 
-# SSE helper function
-def sse_response(generator_func):
-    """Helper to create SSE responses"""
-    def generate():
-        for data in generator_func():
-            yield f"data: {json.dumps(data)}\n\n"
-    return Response(generate(), mimetype='text/event-stream')
+class _StreamBroadcaster:
+    """Fan-out broadcaster: one background generator thread pushes to all SSE clients.
+
+    This means N browser tabs share one generator instead of each running their own,
+    keeping PIL encodes / subprocess forks constant regardless of how many tabs are open.
+    """
+
+    def __init__(self, generator_factory):
+        self._generator_factory = generator_factory
+        self._clients: set = set()
+        self._lock = threading.Lock()
+        self._thread: threading.Thread | None = None
+
+    def subscribe(self) -> queue.Queue:
+        q: queue.Queue = queue.Queue(maxsize=5)
+        with self._lock:
+            self._clients.add(q)
+            if not (self._thread and self._thread.is_alive()):
+                self._thread = threading.Thread(target=self._broadcast, daemon=True)
+                self._thread.start()
+        return q
+
+    def unsubscribe(self, q: queue.Queue) -> None:
+        with self._lock:
+            self._clients.discard(q)
+
+    def _broadcast(self):
+        for data in self._generator_factory():
+            with self._lock:
+                if not self._clients:
+                    continue
+                dead = set()
+                for q in self._clients:
+                    try:
+                        q.put_nowait(data)
+                    except queue.Full:
+                        dead.add(q)
+                self._clients -= dead
 
 # System status generator for SSE
 def system_status_generator():
@@ -596,20 +629,50 @@ def logs_generator():
 
         time.sleep(5)  # Update every 5 seconds (reduced frequency for better performance)
 
+# One broadcaster per stream — shared across all SSE clients
+_stats_broadcaster = _StreamBroadcaster(system_status_generator)
+_display_broadcaster = _StreamBroadcaster(display_preview_generator)
+_logs_broadcaster = _StreamBroadcaster(logs_generator)
+
+
+def _sse_stream(broadcaster: _StreamBroadcaster) -> Response:
+    """Return a streaming SSE response backed by a shared broadcaster."""
+    q = broadcaster.subscribe()
+
+    def generate():
+        try:
+            while True:
+                try:
+                    data = q.get(timeout=30)
+                    yield f"data: {json.dumps(data)}\n\n"
+                except queue.Empty:
+                    # Send an SSE comment heartbeat to keep the connection alive
+                    # through proxies that close idle connections.
+                    yield ": heartbeat\n\n"
+        except GeneratorExit:
+            pass
+        finally:
+            broadcaster.unsubscribe(q)
+
+    return Response(generate(), mimetype='text/event-stream')
+
+
 # SSE endpoints
 @app.route('/api/v3/stream/stats')
 def stream_stats():
-    return sse_response(system_status_generator)
+    return _sse_stream(_stats_broadcaster)
 
 @app.route('/api/v3/stream/display')
 def stream_display():
-    return sse_response(display_preview_generator)
+    return _sse_stream(_display_broadcaster)
 
 @app.route('/api/v3/stream/logs')
 def stream_logs():
-    return sse_response(logs_generator)
+    return _sse_stream(_logs_broadcaster)
 
-# Exempt SSE streams from CSRF and add rate limiting
+# Exempt SSE streams from CSRF and apply a generous rate limit.
+# SSE connections are long-lived HTTP requests, not repeated API calls, so the
+# tight "20 per minute" default would be exhausted quickly on reconnects.
 if csrf:
     csrf.exempt(stream_stats)
     csrf.exempt(stream_display)
@@ -617,9 +680,9 @@ if csrf:
     # Note: api_v3 blueprint is exempted above after registration
 
 if limiter:
-    limiter.limit("20 per minute")(stream_stats)
-    limiter.limit("20 per minute")(stream_display)
-    limiter.limit("20 per minute")(stream_logs)
+    limiter.limit("200 per minute")(stream_stats)
+    limiter.limit("200 per minute")(stream_display)
+    limiter.limit("200 per minute")(stream_logs)
 
 # Main route - redirect to v3 interface as default
 @app.route('/')

web_interface/blueprints/api_v3.py

@@ -6542,7 +6542,7 @@ def scan_wifi_networks():
         ap_was_active = wifi_manager._is_ap_mode_active()
 
         # Perform the scan (this will handle AP mode disabling/enabling internally)
-        networks, _was_cached = wifi_manager.scan_networks()
+        networks = wifi_manager.scan_networks()
 
         # Convert to dict format
         networks_data = [
@@ -6680,9 +6680,7 @@ def enable_ap_mode():
         from src.wifi_manager import WiFiManager
 
         wifi_manager = WiFiManager()
-        _force_raw = (request.get_json(silent=True) or {}).get('force', False)
-        force = _force_raw is True or (isinstance(_force_raw, str) and _force_raw.lower() in ('true', '1'))
-        success, message = wifi_manager.enable_ap_mode(force=force)
+        success, message = wifi_manager.enable_ap_mode()
 
         if success:
             return jsonify({

web_interface/static/v3/app.js

@@ -51,7 +51,7 @@ document.body.addEventListener('htmx:afterRequest', function(event) {
     }
 });
 
-// SSE reconnection helper
+// SSE reconnection helper — closes and reopens both SSE streams.
 window.reconnectSSE = function() {
     if (window.statsSource) {
         window.statsSource.close();
@@ -65,8 +65,9 @@ window.reconnectSSE = function() {
     if (window.displaySource) {
         window.displaySource.close();
         window.displaySource = new EventSource('/api/v3/stream/display');
-        window.displaySource.onmessage = function() {
-            // Handle display updates
+        window.displaySource.onmessage = function(event) {
+            const data = JSON.parse(event.data);
+            if (typeof updateDisplayPreview === 'function') updateDisplayPreview(data);
         };
     }
 };

web_interface/templates/v3/base.html

@@ -1370,33 +1370,58 @@
 
     <!-- SSE connection for real-time updates -->
     <script>
-        // Connect to SSE streams
-        const statsSource = new EventSource('/api/v3/stream/stats');
-        const displaySource = new EventSource('/api/v3/stream/display');
+        // Assign to window so reconnectSSE() in app.js can reach them.
+        window.statsSource = new EventSource('/api/v3/stream/stats');
+        window.displaySource = new EventSource('/api/v3/stream/display');
 
-        statsSource.onmessage = function(event) {
+        window.statsSource.onmessage = function(event) {
             const data = JSON.parse(event.data);
             updateSystemStats(data);
         };
 
-        displaySource.onmessage = function(event) {
+        window.displaySource.onmessage = function(event) {
             const data = JSON.parse(event.data);
             updateDisplayPreview(data);
         };
 
-        // Connection status
-        statsSource.addEventListener('open', function() {
-            document.getElementById('connection-status').innerHTML = `
-                <div class="w-2 h-2 bg-green-500 rounded-full"></div>
-                <span class="text-gray-600">Connected</span>
-            `;
+        function _setConnectionStatus(connected, reconnecting) {
+            const el = document.getElementById('connection-status');
+            if (!el) return;
+            if (connected) {
+                el.innerHTML = `
+                    <div class="w-2 h-2 bg-green-500 rounded-full"></div>
+                    <span class="text-gray-600">Connected</span>
+                `;
+            } else if (reconnecting) {
+                el.innerHTML = `
+                    <div class="w-2 h-2 bg-yellow-500 rounded-full animate-pulse"></div>
+                    <span class="text-gray-600">Reconnecting…</span>
+                `;
+            } else {
+                el.innerHTML = `
+                    <div class="w-2 h-2 bg-red-500 rounded-full"></div>
+                    <span class="text-gray-600" title="Connection lost — try refreshing the page">Disconnected</span>
+                `;
+            }
+        }
+
+        var _statsErrorCount = 0;
+        window.statsSource.addEventListener('open', function() {
+            _statsErrorCount = 0;
+            _setConnectionStatus(true, false);
         });
 
-        statsSource.addEventListener('error', function() {
-            document.getElementById('connection-status').innerHTML = `
-                <div class="w-2 h-2 bg-red-500 rounded-full"></div>
-                <span class="text-gray-600">Disconnected</span>
-            `;
+        window.statsSource.addEventListener('error', function() {
+            _statsErrorCount++;
+            // EventSource readyState 0 = CONNECTING (auto-retrying), 2 = CLOSED
+            var reconnecting = window.statsSource.readyState === EventSource.CONNECTING;
+            _setConnectionStatus(false, reconnecting && _statsErrorCount <= 3);
+        });
+
+        window.displaySource.addEventListener('error', function() {
+            // Display stream errors don't change the status badge but log to console
+            // so failures aren't completely silent.
+            console.warn('LEDMatrix: display preview stream error (readyState=' + window.displaySource.readyState + ')');
         });
 
         function updateSystemStats(data) {