Add scripts/expose.sh: tailcat tunnel for remote access

tailcat (Tailscale data plane, no control plane) forwards the VM's
web UI and SSH ports to another machine via a stable saved-key
address; outbound-only, so it works through the nested slirp NAT.

README.md

@@ -54,6 +54,23 @@ scripts/run.sh
 - Ops SSH: `ssh -i configs/ssh/id_ed25519 -p 2222 marvin@localhost`
 - QEMU runs foreground; quit with `ctrl-a x`
 
+### Access from another machine (tailcat)
+
+`localhost` above is the machine running QEMU. To reach the VM from
+elsewhere, run `scripts/expose.sh` next to it — a tailcat tunnel
+(WireGuard over Tailscale's DERP relays, outbound-only, no account):
+
+```
+host $ scripts/expose.sh
+# 🐈 Server listening with saved key "default": tcpGFwWCCH...
+
+your $ tailcat forward tcpGFwWCCH... 8080:8080 2222:2222
+```
+
+Then browse `http://localhost:8080` / `ssh -p 2222 marvin@localhost`
+from *your* machine. The address is stable across VM restarts (saved
+key) and is a bearer secret — share it only privately.
+
 ### LLM backend
 
 `[models.tensorx]` in `configs/turnstone/config.toml` points at the

scripts/expose.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Expose the turnstone VM to another machine via tailcat (Tailscale's
+# data plane without its control plane — outbound-only, works through
+# the nested slirp NAT).
+#
+#   scripts/expose.sh            # foreground; ctrl-c to stop
+#
+# Prints a stable tailcat address (saved key at
+# ~/.config/tailcat/keys/default.private.json). On the client machine:
+#
+#   tailcat forward <tc-address> 8080:8080 2222:2222
+#
+# then browse http://localhost:8080 and ssh -p 2222 as usual.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+TC="${TAILCAT_BIN:-$HOME/.local/bin/tailcat}"
+PORTS="${TAILCAT_PORTS:-8080,2222}"
+
+if ! command -v "$TC" >/dev/null 2>&1; then
+  echo "tailcat not found at $TC" >&2
+  echo "install it first: https://github.com/tailscale/tailcat (INSTALL.md)" >&2
+  exit 1
+fi
+
+# Stable address across restarts: create the saved key once
+if [ ! -f "$HOME/.config/tailcat/keys/default.private.json" ]; then
+  "$TC" genkey --key=default
+fi
+
+exec "$TC" serve --key=default "$PORTS"