Add remote exec start script (#17059)

Just pass an SSH host
```
./scripts/start-codex-exec.sh codex-remote
```

scripts/start-codex-exec.sh

@@ -0,0 +1,182 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+usage() {
+  echo "Usage: $0 HOST [RSYNC_OPTION]..." >&2
+}
+
+if [[ $# -lt 1 ]]; then
+  usage
+  exit 2
+fi
+
+case "$1" in
+  -h|--help)
+    usage
+    exit 0
+    ;;
+esac
+
+remote_host="$1"
+shift
+
+remote_path='~/code/codex-sync'
+local_exec_server_port="${CODEX_REMOTE_EXEC_SERVER_LOCAL_PORT:-8765}"
+remote_exec_server_start_timeout_seconds="${CODEX_REMOTE_EXEC_SERVER_START_TIMEOUT_SECONDS:-15}"
+
+remote_exec_server_pid=''
+remote_exec_server_log_path=''
+remote_exec_server_pid_path=''
+
+cleanup() {
+  local exit_code=$?
+
+  trap - EXIT INT TERM
+
+  if [[ -n "${remote_exec_server_pid_path}" ]]; then
+    ssh "${remote_host}" \
+      "if [[ -f '${remote_exec_server_pid_path}' ]]; then kill \$(cat '${remote_exec_server_pid_path}') >/dev/null 2>&1 || true; fi; rm -f '${remote_exec_server_pid_path}' '${remote_exec_server_log_path}'" \
+      >/dev/null 2>&1 || true
+  fi
+
+  exit "${exit_code}"
+}
+
+trap cleanup EXIT INT TERM
+
+if ! command -v git >/dev/null 2>&1; then
+  echo "git is required" >&2
+  exit 1
+fi
+
+if ! command -v ssh >/dev/null 2>&1; then
+  echo "ssh is required" >&2
+  exit 1
+fi
+
+if ! command -v rsync >/dev/null 2>&1; then
+  echo "local rsync is required" >&2
+  exit 1
+fi
+
+repo_root="$(git rev-parse --show-toplevel 2>/dev/null)" || {
+  echo "run this script from inside a git repository" >&2
+  exit 1
+}
+
+ssh "${remote_host}" "mkdir -p ${remote_path}"
+
+if ! ssh "${remote_host}" 'command -v rsync >/dev/null 2>&1'; then
+  echo "remote rsync is required on ${remote_host}" >&2
+  exit 1
+fi
+
+sync_instance_id="$(date +%s)-$$"
+
+rsync \
+  --archive \
+  --compress \
+  --human-readable \
+  --itemize-changes \
+  --exclude '.git/' \
+  --exclude 'codex-rs/target/' \
+  --filter=':- .gitignore' \
+  "$@" \
+  "${repo_root}/" \
+  "${remote_host}:${remote_path}/" \
+  >&2
+
+remote_exec_server_log_path="/tmp/codex-exec-server-${sync_instance_id}.log"
+remote_exec_server_pid_path="/tmp/codex-exec-server-${sync_instance_id}.pid"
+
+remote_start_output="$(
+  ssh "${remote_host}" bash -s -- \
+    "${remote_exec_server_log_path}" \
+    "${remote_exec_server_pid_path}" \
+    "${remote_exec_server_start_timeout_seconds}" <<'EOF'
+set -euo pipefail
+
+remote_exec_server_log_path="$1"
+remote_exec_server_pid_path="$2"
+remote_exec_server_start_timeout_seconds="$3"
+remote_repo_root="$HOME/code/codex-sync"
+remote_codex_rs="$remote_repo_root/codex-rs"
+
+cd "${remote_codex_rs}"
+cargo build -p codex-exec-server --bin codex-exec-server
+
+rm -f "${remote_exec_server_log_path}" "${remote_exec_server_pid_path}"
+nohup ./target/debug/codex-exec-server --listen ws://127.0.0.1:0 \
+  >"${remote_exec_server_log_path}" 2>&1 &
+remote_exec_server_pid="$!"
+echo "${remote_exec_server_pid}" >"${remote_exec_server_pid_path}"
+
+deadline=$((SECONDS + remote_exec_server_start_timeout_seconds))
+while (( SECONDS < deadline )); do
+  if [[ -s "${remote_exec_server_log_path}" ]]; then
+    listen_url="$(head -n 1 "${remote_exec_server_log_path}" || true)"
+    if [[ "${listen_url}" == ws://* ]]; then
+      printf 'remote_exec_server_pid=%s\n' "${remote_exec_server_pid}"
+      printf 'remote_exec_server_log_path=%s\n' "${remote_exec_server_log_path}"
+      printf 'listen_url=%s\n' "${listen_url}"
+      exit 0
+    fi
+  fi
+
+  if ! kill -0 "${remote_exec_server_pid}" >/dev/null 2>&1; then
+    cat "${remote_exec_server_log_path}" >&2 || true
+    echo "remote exec server exited before reporting a listen URL" >&2
+    exit 1
+  fi
+
+  sleep 0.1
+done
+
+cat "${remote_exec_server_log_path}" >&2 || true
+echo "timed out waiting for remote exec server listen URL" >&2
+exit 1
+EOF
+)"
+
+listen_url=''
+while IFS='=' read -r key value; do
+  case "${key}" in
+    remote_exec_server_pid)
+      remote_exec_server_pid="${value}"
+      ;;
+    remote_exec_server_log_path)
+      remote_exec_server_log_path="${value}"
+      ;;
+    listen_url)
+      listen_url="${value}"
+      ;;
+  esac
+done <<< "${remote_start_output}"
+
+if [[ -z "${remote_exec_server_pid}" || -z "${listen_url}" ]]; then
+  echo "failed to parse remote exec server startup output" >&2
+  exit 1
+fi
+
+remote_exec_server_port="${listen_url##*:}"
+if [[ -z "${remote_exec_server_port}" || "${remote_exec_server_port}" == "${listen_url}" ]]; then
+  echo "failed to parse remote exec server port from ${listen_url}" >&2
+  exit 1
+fi
+
+echo "Remote exec server: ${listen_url}"
+echo "Remote exec server log: ${remote_exec_server_log_path}"
+echo "Press Ctrl-C to stop the SSH tunnel and remote exec server."
+echo "Start codex via: "
+echo "  CODEX_EXEC_SERVER_URL=ws://127.0.0.1:${local_exec_server_port} codex -C /tmp"
+
+ssh \
+  -nNT \
+  -o ControlMaster=no \
+  -o ControlPath=none \
+  -o ExitOnForwardFailure=yes \
+  -o ServerAliveInterval=30 \
+  -o ServerAliveCountMax=3 \
+  -L "${local_exec_server_port}:127.0.0.1:${remote_exec_server_port}" \
+  "${remote_host}"