fix: fall back to IPv4 bind address when IPv6 is disabled

Commit 84a119f switched --bind-addr to "[::]:8443" for dual-stack, but
binding fails with EAFNOSUPPORT when IPv6 is disabled in the kernel,
leaving code-server unreachable. Detect IPv6 via /proc/net/if_inet6 and
fall back to 0.0.0.0:8443 when it is unavailable.

Author: pinguinfuss

root/etc/s6-overlay/s6-rc.d/svc-code-server/run

@@ -18,12 +18,21 @@ if [[ -z ${PWA_APPNAME} ]]; then
     PWA_APPNAME="code-server"
 fi
 
+# Bind to the IPv6 wildcard (dual-stack, also serves IPv4) when IPv6 is
+# available, otherwise fall back to the IPv4 wildcard. Binding to "[::]"
+# fails outright on hosts/containers where IPv6 is disabled.
+if [[ -e /proc/net/if_inet6 ]]; then
+    BIND_ADDR="[::]:8443"
+else
+    BIND_ADDR="0.0.0.0:8443"
+fi
+
 if [[ -z ${LSIO_NON_ROOT_USER} ]]; then
     exec \
         s6-notifyoncheck -d -n 300 -w 1000 -c "nc -z 127.0.0.1 8443" \
             s6-setuidgid abc \
                 /app/code-server/bin/code-server \
-                    --bind-addr "[::]:8443" \
+                    --bind-addr "${BIND_ADDR}" \
                     --user-data-dir /config/data \
                     --extensions-dir /config/extensions \
                     --disable-telemetry \