feat(network): wlan0 fallback if T3U dongle is absent

- PRIMARY_INTERFACE=wlan1, FALLBACK_INTERFACE=wlan0
- resolve_interface() checks /sys/class/net at startup and picks whichever exists
- INTERFACE is module-level, so all functions use the correct iface automatically
- restore_fallback() now also tries home-wifi-fb / Hotspot on wlan0 if wlan1 is primary but failed
- install_netwatch.sh creates home-wifi-fb profile on wlan0 (lower autoconnect-priority=5)
- wlan0 stays managed=yes (fallback) instead of being hard-disabled
- Status JSON now includes 'interface' field for diagnostics

Co-authored-by: Copilot <[email protected]>

deploy/yaris_uplink.py

@@ -12,7 +12,8 @@ import uuid
 PHONE_CONNECTION = "phone-hotspot"
 HOME_CONNECTION = "home-wifi"
 AP_CONNECTION = "Hotspot"
-INTERFACE = "wlan1"       # TP-Link T3U dongle — all client + AP traffic
+PRIMARY_INTERFACE = "wlan1"    # TP-Link T3U dongle — preferred
+FALLBACK_INTERFACE = "wlan0"   # onboard — used if T3U is absent
 STATUS_PATH = "/var/lib/yaris-obd/uplink-status.json"
 PHONE_KEYFILE = (
     "/etc/NetworkManager/system-connections/"
@@ -24,6 +25,24 @@ class UplinkError(RuntimeError):
     pass
 
 
+def _interface_exists(iface):
+    """Return True if the kernel sees this network interface."""
+    return os.path.exists(f"/sys/class/net/{iface}")
+
+
+def resolve_interface():
+    """Return PRIMARY_INTERFACE if it exists, else FALLBACK_INTERFACE."""
+    if _interface_exists(PRIMARY_INTERFACE):
+        return PRIMARY_INTERFACE
+    if _interface_exists(FALLBACK_INTERFACE):
+        return FALLBACK_INTERFACE
+    return PRIMARY_INTERFACE   # return primary anyway; nmcli will error clearly
+
+
+# Module-level convenience — resolved once at startup.
+INTERFACE = resolve_interface()
+
+
 def run_nmcli(*args, timeout=45, check=True):
     process = subprocess.run(
         ["nmcli", *args],
@@ -149,6 +168,7 @@ def write_status(action, error=None):
     status = {
         "action": action,
         "active_connection": current,
+        "interface": INTERFACE,
         "error": error,
         "last_phone_ip": last_phone_ip,
         "updated_at": time.time(),
@@ -182,6 +202,17 @@ def restore_fallback():
     if activate(HOME_CONNECTION):
         write_status("connected_home")
         return True
+    # If the primary interface (wlan1) failed, try the wlan0 fallback profiles
+    if INTERFACE == PRIMARY_INTERFACE and _interface_exists(FALLBACK_INTERFACE):
+        # Temporarily try connections bound to wlan0
+        for conn in (f"{HOME_CONNECTION}-fb", AP_CONNECTION):
+            proc = subprocess.run(
+                ["nmcli", "--wait", "30", "connection", "up", conn],
+                capture_output=True, text=True, timeout=35,
+            )
+            if proc.returncode == 0:
+                write_status(f"fallback_wlan0_{conn}")
+                return True
     if activate(AP_CONNECTION):
         write_status("restored_local_hotspot")
         return True