tools: wireless-adb beacon — self-healing bridge across drops + port rotation

The phone's wireless-debug port rotates and the bridge drops; this makes
adb reconnect automatically. Three pieces:
- adb-beacon (Android dev app): reads adbd's own mDNS advertisement
  (_adb-tls-connect._tcp) via NsdManager for the live connect port — no
  root, no Shizuku — plus the wlan0 IPv4, and POSTs {ip,port} to fmr every
  time it changes (continuous NSD discovery catches rotation in seconds).
  Foreground service (specialUse) so it survives backgrounding.
- tools/adb-beacon/receiver.py: ~30-line rendezvous on fmr:9099 (secret-
  gated POST stores the latest endpoint; GET returns it). Deployed as
  echolot-adb-beacon.service.
- PC connector polls the endpoint and keeps `adb connect` current.

Dev tooling, separate from the product. Bootstrap: sideload the beacon
APK once (no adb needed); thereafter adb self-heals for everything.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

echolot-app/adb-beacon/build.gradle.kts

@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+plugins {
+    // AGP 9 built-in Kotlin (no kotlin.android — see core-probe note).
+    alias(libs.plugins.android.application)
+}
+
+// Dev tool (NOT the product app): reports this phone's rotating wireless-debug
+// endpoint to the fmr beacon so the PC can keep `adb connect` current. Reads
+// the connect port from adbd's own mDNS advertisement (_adb-tls-connect._tcp)
+// via NsdManager — no root, no Shizuku.
+android {
+    namespace = "app.echo_lot.adbbeacon"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "app.echo_lot.adbbeacon"
+        minSdk = 26
+        targetSdk = 36
+        versionCode = 1
+        versionName = "0.1.0"
+        // Prefilled beacon config (dev tool — secret in the APK is fine).
+        buildConfigField("String", "BEACON_URL", "\"http://fmr-1.echo-lot.app:9099/beacon\"")
+        buildConfigField("String", "BEACON_SECRET", "\"D4OmG5gGJsElqVVbtYIZbR\"")
+    }
+    buildTypes { release { isMinifyEnabled = false } }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+    buildFeatures { buildConfig = true }
+}
+
+dependencies {
+    implementation(libs.kotlinx.coroutines.android)
+    implementation(libs.androidx.core.ktx)
+    implementation("androidx.activity:activity:1.9.3")
+}