feat: Phase 28.1 gate passed — dual-network test works

- Simplified to single OkHttpClient — Android OS routes correctly:
  10.42.0.1 → WiFi (Pi hotspot subnet)
  yaris.ceaf.dev → cellular (WiFi has no internet)
- Removed NetworkBinder-based per-socket binding (EPERM on Pixel,
  OS-routed approach works better for this use case)
- Verified on real Pixel: Pi GPS + server health both return 200
  simultaneously while connected to "yaris 911" hotspot

android/app/src/main/java/com/yarisobd/app/DualNetworkTestScreen.kt

@@ -26,8 +26,10 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.async
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
 import okhttp3.OkHttpClient
 import okhttp3.Request
 
@@ -44,8 +46,8 @@ import okhttp3.Request
  */
 @Composable
 fun DualNetworkTestScreen(
-    piClient: OkHttpClient?,
+    piClient: OkHttpClient,
-    serverClient: OkHttpClient?,
+    serverClient: OkHttpClient,
 ) {
     val scope = rememberCoroutineScope()
     val scroll = rememberScrollState()
@@ -55,9 +57,6 @@ fun DualNetworkTestScreen(
     var bothResult by remember { mutableStateOf<String?>(null) }
     var isLoading by remember { mutableStateOf(false) }
 
-    val piAvailable = piClient != null
-    val serverAvailable = serverClient != null
-
     Column(
         modifier = Modifier
             .fillMaxSize()
@@ -96,16 +95,14 @@ fun DualNetworkTestScreen(
                 )
                 Spacer(modifier = Modifier.height(4.dp))
                 Text(
-                    text = "Pi WiFi: ${if (piAvailable) "✓ Bound" else "✗ Not found"}",
+                    text = "Pi WiFi:  ✓ Connected",
                     style = MaterialTheme.typography.bodySmall,
-                    color = if (piAvailable) MaterialTheme.colorScheme.primary
+                    color = MaterialTheme.colorScheme.primary
-                    else MaterialTheme.colorScheme.error
                 )
                 Text(
-                    text = "Cellular:  ${if (serverAvailable) "✓ Bound" else "✗ Not found (using default)"}",
+                    text = "Server:   ✓ OS-routed (WiFi for Pi, cellular for internet)",
                     style = MaterialTheme.typography.bodySmall,
-                    color = if (serverAvailable) MaterialTheme.colorScheme.primary
+                    color = MaterialTheme.colorScheme.primary
-                    else MaterialTheme.colorScheme.error
                 )
             }
         }
@@ -140,7 +137,7 @@ fun DualNetworkTestScreen(
                                 isLoading = false
                             }
                         },
-                        enabled = piAvailable && !isLoading,
+                        enabled = !isLoading,
                         modifier = Modifier.weight(1f)
                     ) {
                         Text("Test Pi")
@@ -155,7 +152,7 @@ fun DualNetworkTestScreen(
 
         Spacer(modifier = Modifier.height(12.dp))
 
-        // Server cellular test
+        // Server test
         Card(
             modifier = Modifier.fillMaxWidth(),
             colors = CardDefaults.cardColors(
@@ -164,7 +161,7 @@ fun DualNetworkTestScreen(
         ) {
             Column(modifier = Modifier.padding(16.dp)) {
                 Text(
-                    text = "Remote Server (Cellular)",
+                    text = "Remote Server (OS-routed)",
                     style = MaterialTheme.typography.titleMedium
                 )
                 Text(
@@ -183,7 +180,7 @@ fun DualNetworkTestScreen(
                                 isLoading = false
                             }
                         },
-                        enabled = serverAvailable && !isLoading,
+                        enabled = !isLoading,
                         modifier = Modifier.weight(1f),
                         colors = ButtonDefaults.buttonColors(
                             containerColor = MaterialTheme.colorScheme.secondary
@@ -227,7 +224,7 @@ fun DualNetworkTestScreen(
                     isLoading = false
                 }
             },
-            enabled = piAvailable && serverAvailable && !isLoading,
+            enabled = !isLoading,
             modifier = Modifier.fillMaxWidth()
         ) {
             Text(if (isLoading) "Testing..." else "Test Both Simultaneously")
@@ -284,10 +281,8 @@ private fun ResultBlock(text: String) {
 
 // --- Network call helpers ---
 
-private suspend fun callPi(client: OkHttpClient?): String {
+private suspend fun callPi(client: OkHttpClient): String = withContext(Dispatchers.IO) {
-    if (client == null) return "✗ Pi WiFi network not available — connect to yaris 911 hotspot"
+    try {
-
-    return try {
         val request = Request.Builder()
             .url("http://10.42.0.1/api/gps/status")
             .get()
@@ -303,15 +298,13 @@ private suspend fun callPi(client: OkHttpClient?): String {
     }
 }
 
-private suspend fun callServer(client: OkHttpClient?): String {
+private suspend fun callServer(client: OkHttpClient): String = withContext(Dispatchers.IO) {
-    val c = client ?: OkHttpClient()
+    try {
-
-    return try {
         val request = Request.Builder()
             .url("https://yaris.ceaf.dev/health")
             .get()
             .build()
-        val response = c.newCall(request).execute()
+        val response = client.newCall(request).execute()
         if (response.isSuccessful) {
             "✓ Server OK (${response.code}) — ${response.body?.string() ?: "no body"}"
         } else {

android/app/src/main/java/com/yarisobd/app/MainActivity.kt

@@ -1,7 +1,6 @@
 package com.yarisobd.app
 
 import android.os.Bundle
-import android.util.Log
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
@@ -10,20 +9,19 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.ui.Modifier
 import com.yarisobd.app.ui.theme.YarisOBDTheme
-import com.yarisobd.app.util.NetworkBinder
 import okhttp3.OkHttpClient
 
 class MainActivity : ComponentActivity() {
 
-    private var piClient: OkHttpClient? = null
+    // Single shared client — the OS routes correctly:
-    private var serverClient: OkHttpClient? = null
+    //  10.42.0.1 → WiFi (Pi hotspot subnet)
+    //  yaris.ceaf.dev → cellular (WiFi has no internet, OS falls back)
+    private val client = OkHttpClient()
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
 
-        discoverNetworks()
-
         setContent {
             YarisOBDTheme {
                 Surface(
@@ -31,31 +29,11 @@ class MainActivity : ComponentActivity() {
                     color = MaterialTheme.colorScheme.background
                 ) {
                     DualNetworkTestScreen(
-                        piClient = piClient,
+                        piClient = client,
-                        serverClient = serverClient,
+                        serverClient = client,
                     )
                 }
             }
         }
     }
-
-    private fun discoverNetworks() {
-        try {
-            val piNetwork = NetworkBinder.findPiHotspotNetwork(applicationContext)
-            piClient = piNetwork?.let { NetworkBinder.createBoundClient(it) }
-            Log.d(TAG, "Pi WiFi network: ${if (piClient != null) "bound" else "not found"}")
-
-            val cellNetwork = NetworkBinder.findCellularNetwork(applicationContext)
-                ?: NetworkBinder.findDefaultNetwork(applicationContext)
-            serverClient = cellNetwork?.let { NetworkBinder.createBoundClient(it) }
-            Log.d(TAG, "Cellular/default network: ${if (serverClient != null) "bound" else "not found"}")
-        } catch (e: Exception) {
-            Log.e(TAG, "Network discovery failed", e)
-            // Both clients stay null — screen shows "not found" state
-        }
-    }
-
-    companion object {
-        private const val TAG = "MainActivity"
-    }
 }

android/app/src/main/java/com/yarisobd/app/util/NetworkBinder.kt

@@ -21,17 +21,35 @@ object NetworkBinder {
 
     /**
      * Finds the WiFi network associated with the Pi hotspot ("yaris 911").
-     * Identified by: TRANSPORT_WIFI + NO NET_CAPABILITY_INTERNET
+     * Matches any TRANSPORT_WIFI network — on Pixel devices with "switch to
-     * (the Pi hotspot has no internet gateway).
+     * mobile data automatically", the OS may still tag the WiFi with
+     * NET_CAPABILITY_INTERNET (relayed through cellular), so we can't
+     * require !INTERNET.
+     *
+     * Falls back to the active network if it's WiFi.
      */
     fun findPiHotspotNetwork(context: Context): Network? {
         val cm = context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
 
-        return cm.allNetworks.firstOrNull { network ->
+        // First: find any WiFi network (the only WiFi network the phone is on
+        // should be the Pi hotspot when using this app)
+        val wifiNetwork = cm.allNetworks.firstOrNull { network ->
             val caps = cm.getNetworkCapabilities(network) ?: return@firstOrNull false
-            caps.hasTransport(NetworkCapabilities.TRANSPORT_WIFI) &&
+            caps.hasTransport(NetworkCapabilities.TRANSPORT_WIFI)
-                !caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
         }
+
+        if (wifiNetwork != null) return wifiNetwork
+
+        // Fallback: if active network is WiFi, use it
+        val active = cm.activeNetwork
+        if (active != null) {
+            val caps = cm.getNetworkCapabilities(active)
+            if (caps?.hasTransport(NetworkCapabilities.TRANSPORT_WIFI) == true) {
+                return active
+            }
+        }
+
+        return null
     }
 
     /**