Add shell and return helpers

HOW_TO_USE.md

@@ -36,14 +36,14 @@ Find the new Ethernet interface with `ip link`. Then:
 
 ```sh
 nmcli device connect <interface>
-telnet 10.42.0.2
+tools/shell.sh
 ```
 
 If DHCP is unavailable:
 
 ```sh
 sudo ip addr add 10.42.0.1/24 dev <interface>
-telnet 10.42.0.2
+tools/shell.sh
 ```
 
 Run one command without telnet:
@@ -55,7 +55,7 @@ python3 tools/qkx_sh.py 'uname -a'
 ## 5. Return to Android
 
 ```sh
-python3 tools/qkx_sh.py 'echo r > /proc/qkx_bootdone'
+tools/return-android.sh
 ```
 
 ## Logs

tools/return-android.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Ask the target kernel for a DRAM-preserving warm reset back to Android.
+set -e
+HERE=$(cd "$(dirname "$0")" && pwd)
+exec python3 "$HERE/qkx_sh.py" 'echo r > /proc/qkx_bootdone' 5

tools/shell.sh

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+# Open the BusyBox shell on the kexec target.
+exec telnet "${QKX_HOST:-10.42.0.2}" 23