feat(sidecar): reach USB devices via the adb server by serial

sidecar/src/main/kotlin/dev/sanderling/sidecar/DriverBackend.kt

@@ -630,12 +630,24 @@ class MaestroDriverBackend(private val serial: String?) : DriverBackend {
     }
 }
 
-private fun buildDadb(serial: String?): dadb.Dadb {
-    return if (serial == null) {
-        dadb.Dadb.create("localhost", 5555)
-    } else {
-        dadb.Dadb.create(serial.substringBefore(":"), serial.substringAfter(":").toIntOrNull() ?: 5555)
+internal sealed interface DadbTarget {
+    data class Tcp(val host: String, val port: Int) : DadbTarget
+    data class Server(val serial: String) : DadbTarget
 }
+
+// A host:port serial connects to adbd directly; any other serial is reached
+// through the adb server, the only path to a USB-attached device. A null serial
+// keeps the emulator loopback default.
+internal fun dadbTargetFor(serial: String?): DadbTarget {
+    if (serial == null) return DadbTarget.Tcp("localhost", 5555)
+    val colon = serial.lastIndexOf(':')
+    val port = if (colon >= 0) serial.substring(colon + 1).toIntOrNull() else null
+    return if (port != null) DadbTarget.Tcp(serial.substring(0, colon), port) else DadbTarget.Server(serial)
+}
+
+private fun buildDadb(serial: String?): dadb.Dadb = when (val target = dadbTargetFor(serial)) {
+    is DadbTarget.Tcp -> dadb.Dadb.create(target.host, target.port)
+    is DadbTarget.Server -> dadb.adbserver.AdbServer.createDadb("localhost", 5037, "host:transport:${target.serial}")
 }
 
 internal fun findBoundsBySelector(root: maestro.TreeNode, selector: String): IntArray? {

sidecar/src/test/kotlin/dev/sanderling/sidecar/DadbTargetTest.kt

@@ -0,0 +1,19 @@
+package dev.sanderling.sidecar
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class DadbTargetTest {
+
+    @Test fun nullSerialDefaultsToEmulatorLoopback() {
+        assertEquals(DadbTarget.Tcp("localhost", 5555), dadbTargetFor(null))
+    }
+
+    @Test fun hostPortSerialConnectsDirectly() {
+        assertEquals(DadbTarget.Tcp("192.168.1.243", 5555), dadbTargetFor("192.168.1.243:5555"))
+    }
+
+    @Test fun usbSerialRoutesThroughAdbServer() {
+        assertEquals(DadbTarget.Server("663c91b1"), dadbTargetFor("663c91b1"))
+    }
+}