Add MacOS sandboxing to isolate script

isolate

@@ -1,12 +1,57 @@
 #!/bin/bash
 
-project_dir=$( pwd -P ) || exit 1
+# macOS does not provide GNU readlink -e. Keep this compatible with Bash 3.2.
-home_dir=$( readlink -e -- "${HOME}" ) || exit 1
+resolve_path() (
+  local path="${1}" links=0 directory
+  [[ "${path}" = /* ]] || path="${PWD}/${path}"
+  while :; do
+    if [[ -d "${path}" ]]; then
+      cd -P -- "${path}" && pwd -P
+      exit "${?}"
+    fi
+    directory="${path%/*}"
+    cd -P -- "${directory:-/}" || exit 1
+    path="${PWD%/}/${path##*/}"
+    if [[ ! -L "${path}" ]]; then
+      if [[ ! -e "${path}" ]]; then
+        echo "Cannot resolve ${1}" >&2
+        exit 1
+      fi
+      printf '%s\n' "${path}"
+      exit
+    fi
+    links=$(( ${links} + 1 ))
+    if [[ "${links}" -gt 40 ]]; then
+      echo "Too many symlinks in ${1}" >&2
+      exit 1
+    fi
+    path=$( readlink "${path}" ) || exit 1
+    [[ "${path}" = /* ]] || path="${PWD}/${path}"
+  done
+)
 
+platform=$( uname -s ) || exit 1
+case "${platform}" in
+  Linux)
     if ! bubblewrap=$( command -v bwrap ); then
       echo "bubblewrap (bwrap) is required" >&2
       exit 1
     fi
+    ;;
+  Darwin)
+    if ! sandbox_exec=$( command -v sandbox-exec ); then
+      echo "sandbox-exec is required on macOS" >&2
+      exit 1
+    fi
+    ;;
+  *)
+    echo "Unsupported platform: ${platform}" >&2
+    exit 1
+    ;;
+esac
+
+project_dir=$( pwd -P ) || exit 1
+home_dir=$( resolve_path "${HOME}" ) || exit 1
 agents=(
   $( command -v claude )
   $( command -v codex )
@@ -39,7 +84,9 @@ declare -a rw_binds
 declare -a bwrap_args
 declare -a bind_sources
 declare -a bind_destinations
+declare -a hidden_paths
 
+if [[ "${platform}" = Linux ]]; then
   ro_binds=(
     /usr
     /lib
@@ -52,6 +99,19 @@ ro_binds=(
     /etc/group
     "${HOME}/sources"
   )
+else
+  # System libraries, certificates, and Intel/Apple Silicon Homebrew installs.
+  # Do not allow all of /System: /System/Volumes/Data also exposes user files.
+  for readonly_path in /System/Library /System/Volumes/Preboot/Cryptexes /System/Cryptexes \
+      /usr /bin /sbin /opt/homebrew \
+      /Library/Apple /Library/Developer /Library/Frameworks /Library/Keychains \
+      /Library/Preferences /private/var/db/dyld /private/var/db/timezone \
+      /etc/resolv.conf /etc/hosts /etc/ssl /etc/passwd /etc/group "${HOME}/sources"; do
+    if [[ -e "${readonly_path}" ]]; then
+      ro_binds+=("${readonly_path}")
+    fi
+  done
+fi
 
 for readonly_path in "${HOME}/.gitconfig" "${HOME}/bin" "${HOME}/.local" "${HOME}/.atuin" "${XDG_RUNTIME_DIR}"; do
   if [[ -e "${readonly_path}" ]]; then
@@ -59,7 +119,7 @@ for readonly_path in "${HOME}/.gitconfig" "${HOME}/bin" "${HOME}/.local" "${HOME
   fi
 done
 
-for readwrite_path in "${HOME}/.claude" "${HOME}/.claude.json" "${HOME}/.local/share/claude" "${HOME}/.pi" "${project_dir}"; do
+for readwrite_path in /tmp "${HOME}/.claude" "${HOME}/.claude.json" "${HOME}/.local/share/claude" "${HOME}/.pi" "${project_dir}"; do
   if [[ -e "${readwrite_path}" ]]; then
     rw_binds+=("${readwrite_path}")
   fi
@@ -67,13 +127,13 @@ done
 
 # Resolve mount sources, but keep the paths applications expect as destinations.
 for readonly_path in "${ro_binds[@]}"; do
-  bind_source=$( readlink -e -- "${readonly_path}" ) || exit 1
+  bind_source=$( resolve_path "${readonly_path}" ) || exit 1
   bwrap_args+=("--ro-bind" "${bind_source}" "${readonly_path}")
   bind_sources+=("${bind_source}")
   bind_destinations+=("${readonly_path}")
 done
 for readwrite_path in "${rw_binds[@]}"; do
-  bind_source=$( readlink -e -- "${readwrite_path}" ) || exit 1
+  bind_source=$( resolve_path "${readwrite_path}" ) || exit 1
   bwrap_args+=("--bind" "${bind_source}" "${readwrite_path}")
   bind_sources+=("${bind_source}")
   bind_destinations+=("${readwrite_path}")
@@ -90,7 +150,8 @@ fi
 # Mask secrets after all directory mounts so later binds cannot expose them.
 for hide_path in "${git_config}" "${git_worktree_config}" "${project_dir}/.env"; do
   if [[ -e "${hide_path}" ]]; then
-    hide_path=$( readlink -e -- "${hide_path}" ) || exit 1
+    hide_path=$( resolve_path "${hide_path}" ) || exit 1
+    hidden_paths+=("${hide_path}")
     bwrap_args+=("--ro-bind" /dev/null "${hide_path}")
     # A symlinked mount can expose the same file at another destination.
     for i in "${!bind_sources[@]}"; do
@@ -104,9 +165,82 @@ for hide_path in "${git_config}" "${git_worktree_config}" "${project_dir}/.env";
   fi
 done
 
+if [[ "${platform}" = Darwin ]]; then
+  # Seatbelt restricts the host filesystem; it does not provide Linux namespaces.
+  # Keep path values out of the profile source by using sandbox-exec parameters.
+  declare -a sandbox_parameters
+  declare -a macos_write_paths
+  macos_profile='(version 1)
+(deny default)
+(allow process-exec process-fork)
+(allow process-info* (target same-sandbox))
+(allow signal (target same-sandbox))
+(allow sysctl-read)
+(allow network*)
+(allow mach-lookup
+  (global-name "com.apple.system.logger")
+  (global-name "com.apple.logd")
+  (global-name "com.apple.system.notification_center")
+  (global-name "com.apple.system.opendirectoryd.libinfo")
+  (global-name "com.apple.system.opendirectoryd.membership")
+  (global-name "com.apple.SystemConfiguration.configd")
+  (global-name "com.apple.trustd.agent")
+  (global-name "com.apple.securityd.xpc"))
+(allow file-read-metadata)
+; The dynamic loader needs access to the root directory, not its contents recursively.
+(allow file-read* (literal "/"))
+(allow file-read* (literal "/dev/random") (literal "/dev/urandom") (literal "/dev/zero"))
+(allow file-read* file-write* file-ioctl
+  (literal "/dev/null") (literal "/dev/tty") (literal "/dev/ptmx")
+  (subpath "/dev/fd") (regex #"^/dev/ttys[0-9]+$"))
+(allow pseudo-tty)'
+
+  add_macos_rule() {
+    local action="${1}" operations="${2}" path="${3}" filter="${4:-literal}"
+    local parameter="PATH_${#sandbox_parameters[@]}"
+    if [[ -z "${4}" && -d "${path}" ]]; then
+      filter=subpath
+    fi
+    sandbox_parameters+=("-D" "${parameter}=${path}")
+    macos_profile+=$'\n'"(${action} ${operations} (${filter} (param \"${parameter}\")))"
+  }
+
+  for readonly_path in "${ro_binds[@]}"; do
+    readonly_path=$( resolve_path "${readonly_path}" ) || exit 1
+    add_macos_rule allow 'file-read*' "${readonly_path}"
+  done
+  for readwrite_path in "${rw_binds[@]}"; do
+    readwrite_path=$( resolve_path "${readwrite_path}" ) || exit 1
+    add_macos_rule allow 'file-read* file-write*' "${readwrite_path}"
+    macos_write_paths+=("${readwrite_path}")
+  done
+
+  # Keep a per-command TMPDIR in addition to access to the shared system /tmp.
+  sandbox_tmp=$( mktemp -d "${TMPDIR:-/tmp}/isolate.XXXXXXXX" ) || exit 1
+  trap 'rm -rf -- "${sandbox_tmp}"' EXIT
+  sandbox_tmp=$( resolve_path "${sandbox_tmp}" ) || exit 1
+  add_macos_rule allow 'file-read* file-write*' "${sandbox_tmp}"
+
+  # Later Seatbelt rules win. Keep these denies after every file-access allow.
+  for hide_path in "${hidden_paths[@]}"; do
+    add_macos_rule deny 'file-read* file-write*' "${hide_path}"
+    # Do not let a writable parent (for example .git) be renamed to bypass the deny.
+    for readwrite_path in "${macos_write_paths[@]}"; do
+      parent_path="${hide_path%/*}"
+      while [[ "${parent_path}" = "${readwrite_path}/"* ]]; do
+        add_macos_rule deny 'file-write-unlink' "${parent_path}" literal
+        parent_path="${parent_path%/*}"
+      done
+    done
+  done
+
+  TMPDIR="${sandbox_tmp}/" "${sandbox_exec}" "${sandbox_parameters[@]}" \
+    -p "${macos_profile}" "${coder}" "${@}"
+  exit "${?}"
+fi
+
 "${bubblewrap}" \
      "${bwrap_args[@]}" \
-     --tmpfs /tmp \
      --proc /proc \
      --dev /dev \
      --share-net \