fix(smoke): capture arp-scan output instead of piping into awk

When host-networking finally gave arp-scan a real LAN to scan, the
first MAC-match emitted a line, awk hit its `exit` clause, closed the
pipe, and arp-scan died from SIGPIPE (exit 141). With `set -o pipefail`
active, that killed the whole smoke-vm.sh run immediately after
"==> starting VM" — no IP discovery, no curl, no prune.

Fix: capture arp-scan's output into a variable first, then let awk
parse a here-string. Same treatment for the `ip neigh show` fallback.
No pipe, no pipefail cascade.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/smoke-vm.sh

@@ -153,14 +153,19 @@ MAC_LOWER="$(echo "$MAC" | tr 'A-Z' 'a-z')"
 IP=""
 deadline=$((SECONDS + 150))
 while (( SECONDS < deadline )); do
+  # Capture-then-parse instead of piping directly into awk. `awk '... exit'`
+  # exits on first match, which SIGPIPEs the upstream arp-scan (exit 141).
+  # With `set -o pipefail` active that kills the whole script — exactly what
+  # happened the first time host-networking gave arp-scan real matches.
+  SCAN=""
   if command -v arp-scan >/dev/null 2>&1; then
-    IP="$(sudo arp-scan --localnet --quiet --ignoredups 2>/dev/null \
+    SCAN="$(sudo arp-scan --localnet --quiet --ignoredups 2>/dev/null || true)"
-          | awk -v m="$MAC_LOWER" 'tolower($2) == m { print $1; exit }')"
+    IP="$(awk -v m="$MAC_LOWER" 'tolower($2) == m { print $1; exit }' <<<"$SCAN")"
   fi
   if [[ -z "$IP" ]] && command -v nmap >/dev/null 2>&1; then
     sudo nmap -sn -T4 192.168.178.0/24 >/dev/null 2>&1 || true
-    IP="$(ip neigh show \
+    NEIGH="$(ip neigh show)"
-          | awk -v m="$MAC_LOWER" 'tolower($5) == m && $1 ~ /^[0-9]/ { print $1; exit }')"
+    IP="$(awk -v m="$MAC_LOWER" 'tolower($5) == m && $1 ~ /^[0-9]/ { print $1; exit }' <<<"$NEIGH")"
   fi
   [[ -n "$IP" ]] && break
   sleep 5