fix(perf): polling-only Socket.IO + channels DB fallback on USB timeout

Werkzeug dev server can't upgrade WebSockets, so every io() upgrade attempt
returned HTTP 500 and clients fell into a polling/upgrade reconnect loop —
visible as 10-15s freezes on app load. Force transports: ['polling'] on
/chat, /console and /logs clients; long-poll keeps real-time pushes
working with ~1-2s latency.

When the MeshCore device briefly stalls, get_channel_info() used to block
on the default 30s timeout per slot, so iterating max_channels slots could
take minutes; in practice only Public answered and the rest timed out,
leaving the UI with just one channel. Drop per-call timeout to 3s, raise
TimeoutError to the caller, and have cli.get_channels() break on first
timeout and merge the remaining slots from the channels table in the DB
(which already mirrors device state via upsert_channel).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/device_manager.py

@@ -14,6 +14,7 @@ import logging
 import struct
 import threading
 import time
+from concurrent.futures import TimeoutError as FuturesTimeoutError
 from typing import Optional, Any, Dict, List, Tuple
 from urllib.parse import urlparse, parse_qs
 
@@ -2187,13 +2188,17 @@ class DeviceManager:
             logger.error(f"Failed to get device info: {e}")
         return {}
 
-    def get_channel_info(self, idx: int) -> Optional[Dict]:
-        """Get info for a specific channel."""
+    def get_channel_info(self, idx: int, timeout: float = 3) -> Optional[Dict]:
+        """Get info for a specific channel.
+
+        Raises TimeoutError when the device fails to respond within `timeout`
+        seconds so callers can distinguish "device sluggish" from "empty slot".
+        """
         if not self.is_connected:
             return None
 
         try:
-            event = self.execute(self.mc.commands.get_channel(idx))
+            event = self.execute(self.mc.commands.get_channel(idx), timeout=timeout)
             if event:
                 data = getattr(event, 'payload', None) or getattr(event, 'data', None)
                 if data and isinstance(data, dict):
@@ -2209,6 +2214,9 @@ class DeviceManager:
                         'secret': secret,
                         'channel_idx': data.get('channel_idx', idx),
                     }
+        except FuturesTimeoutError:
+            # Re-raise so caller can break the loop instead of hammering a stuck device
+            raise
         except Exception as e:
             logger.error(f"Failed to get channel {idx}: {e}")
         return None

app/meshcore/cli.py

@@ -5,6 +5,7 @@ Function signatures preserved for backward compatibility with api.py.
 """
 
 import logging
+from concurrent.futures import TimeoutError as FuturesTimeoutError
 from typing import Tuple, Optional, List, Dict
 from app.config import config
 
@@ -318,18 +319,66 @@ def check_connection() -> bool:
 # =============================================================================
 
 def get_channels() -> Tuple[bool, List[Dict]]:
-    """Get list of configured channels."""
+    """Get list of configured channels.
+
+    When the USB device is briefly unresponsive a single get_channel_info()
+    times out (3 s) and the rest of the slots would too — so we stop hitting
+    the device and merge whatever we got with the locally cached channels in
+    the DB. This guarantees the UI shows all channels instead of just Public.
+    """
     try:
         dm = _get_dm()
         channels = []
+        seen_idx = set()
+        device_partial = False
+
         for idx in range(dm._max_channels):
-            info = dm.get_channel_info(idx)
+            try:
+                info = dm.get_channel_info(idx)
+            except FuturesTimeoutError:
+                logger.warning(
+                    f"get_channels: device timeout at slot {idx} — "
+                    f"falling back to DB for remaining slots"
+                )
+                device_partial = True
+                break
+
             if info and info.get('name'):
                 channels.append({
                     'index': idx,
                     'name': info.get('name', ''),
                     'key': info.get('secret', info.get('key', '')),
                 })
+                seen_idx.add(idx)
+                # Keep the DB in sync with what the device just told us
+                try:
+                    secret_hex = info.get('secret', '') or None
+                    dm.db.upsert_channel(idx, info.get('name', ''), secret_hex)
+                except Exception as e:
+                    logger.debug(f"upsert_channel({idx}) failed: {e}")
+
+        if device_partial:
+            try:
+                for row in dm.db.get_channels():
+                    db_idx = row.get('idx')
+                    if db_idx is None or db_idx in seen_idx:
+                        continue
+                    name = row.get('name') or ''
+                    if not name:
+                        continue
+                    channels.append({
+                        'index': db_idx,
+                        'name': name,
+                        'key': row.get('secret', '') or '',
+                    })
+                channels.sort(key=lambda c: c['index'])
+                logger.info(
+                    f"get_channels: returned {len(channels)} channels "
+                    f"({len(seen_idx)} from device + DB fallback)"
+                )
+            except Exception as e:
+                logger.error(f"get_channels DB fallback failed: {e}")
+
         return True, channels
     except Exception as e:
         logger.error(f"get_channels error: {e}")

app/static/js/app.js

@@ -403,7 +403,8 @@ function connectChatSocket() {
 
     const wsUrl = window.location.origin;
     chatSocket = io(wsUrl + '/chat', {
-        transports: ['websocket', 'polling'],
+        transports: ['polling'],
+        upgrade: false,
         reconnection: true,
         reconnectionDelay: 2000,
         reconnectionDelayMax: 10000,

app/static/js/console.js

@@ -38,7 +38,8 @@ function connectWebSocket() {
 
     try {
         socket = io(wsUrl + '/console', {
-            transports: ['websocket', 'polling'],
+            transports: ['polling'],
+            upgrade: false,
             reconnection: true,
             reconnectionAttempts: Infinity,
             reconnectionDelay: 1000,

app/static/js/dm.js

@@ -125,7 +125,8 @@ function connectChatSocket() {
 
     const wsUrl = window.location.origin;
     chatSocket = io(wsUrl + '/chat', {
-        transports: ['websocket', 'polling'],
+        transports: ['polling'],
+        upgrade: false,
         reconnection: true,
         reconnectionDelay: 2000,
         reconnectionDelayMax: 10000,

app/static/js/logs.js

@@ -33,7 +33,8 @@
 
     // --- WebSocket ---
     const socket = io('/logs', {
-        transports: ['websocket', 'polling'],
+        transports: ['polling'],
+        upgrade: false,
         reconnection: true,
         reconnectionDelay: 2000,
     });