tools: beacon receiver can serve a staged APK on /apk (443)

A test device that can only reach fmr on 443 (LAN blocks other outbound
ports) can pull an APK via its own downloader — more resilient than adb's
sustained transport over flaky wifi. GET /apk serves APK_PATH. (Doesn't
help the Lenovo tablet, which ships no curl; kept for devices that do.)

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

tools/adb-beacon/receiver.py

@@ -49,9 +49,20 @@ class Handler(BaseHTTPRequestHandler):
             self.wfile.write(body)
 
     def do_GET(self):
-        if self.path.rstrip("/") != "/beacon":
+        p = self.path.rstrip("/")
+        if p == "/beacon":
+            return self._send(200, json.dumps(load()).encode())
+        # Dev convenience: serve a staged APK so a device (which can only reach
+        # this host on 443) can pull it via its own curl — more resilient than
+        # adb's sustained transport over a flaky wifi. Path from APK_PATH.
+        if p == "/apk":
+            apk = os.environ.get("APK_PATH", "/tmp/echolot-app.apk")
+            try:
+                with open(apk, "rb") as f:
+                    return self._send(200, f.read(), "application/vnd.android.package-archive")
+            except FileNotFoundError:
+                return self._send(404, b'{"error":"no apk staged"}')
         return self._send(404, b'{"error":"not found"}')
-        self._send(200, json.dumps(load()).encode())
 
     def do_POST(self):
         if self.path.rstrip("/") != "/beacon":