fix: run build in screen session to survive SSH disconnects

Long builds (NVIDIA driver download+compile) would abort on SSH timeout.
Now build runs in a detached screen session on the VM, run-builder.sh
streams the log and waits for completion safely.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/setup-builder.sh

@@ -37,7 +37,8 @@ apk add \
     wget \
     curl \
     tar \
-    xz
+    xz \
+    screen
 
 # --- audit runtime packages (verify they exist in Alpine repos) ---
 echo ""

scripts/run-builder.sh

@@ -35,9 +35,10 @@ echo "=== bee builder ==="
 echo "Builder: ${BUILDER_HOST}"
 echo ""
 
-ssh -o StrictHostKeyChecking=no root@"${BUILDER_HOST}" /bin/sh <<EOF
+ssh -o StrictHostKeyChecking=no root@"${BUILDER_HOST}" /bin/sh <<ENDSSH
 set -e
 REPO=/root/bee
+LOG=/var/log/bee-build.log
 
 if [ ! -d "\$REPO/.git" ]; then
     echo "--- cloning bee repo ---"
@@ -48,9 +49,27 @@ cd "\$REPO"
 echo "--- pulling latest ---"
 git pull --ff-only
 
-echo "--- running build ---"
-sh iso/builder/build-debug.sh ${EXTRA_ARGS}
-EOF
+# Kill any previous build session
+screen -S bee-build -X quit 2>/dev/null || true
+
+echo "--- starting build in screen session (survives SSH disconnect) ---"
+echo "--- log: \$LOG ---"
+screen -dmS bee-build sh -c "sh iso/builder/build-debug.sh ${EXTRA_ARGS} > \$LOG 2>&1; echo \$? > /tmp/bee-build-exit"
+
+# Stream log until build finishes
+echo "--- streaming build log (Ctrl+C safe — build continues on VM) ---"
+while screen -list | grep -q bee-build; do
+    tail -n +1 -f "\$LOG" 2>/dev/null & TAIL_PID=\$!
+    sleep 1
+    while screen -list | grep -q bee-build; do sleep 2; done
+    kill \$TAIL_PID 2>/dev/null || true
+    break
+done
+tail -n 20 "\$LOG" 2>/dev/null || true
+
+EXIT_CODE=\$(cat /tmp/bee-build-exit 2>/dev/null || echo 1)
+exit \$EXIT_CODE
+ENDSSH
 
 echo ""
 echo "=== downloading ISO ==="