fix(plugin): refuse an unset CLAUDE_PLUGIN_ROOT instead of guessing $PWD

[cdeust]

All nine hook commands in .claude-plugin/plugin.json resolved their root as ${CLAUDE_PLUGIN_ROOT:-$PWD}. That fallback cannot ever be correct: scripts/launcher.py lives inside the plugin, never in the user's working directory. When the variable is unset the hook runs python3 against a path that is wrong by construction and reports

can't open file '<cwd>/scripts/launcher.py': [Errno 2] No such file or directory

— an error naming the wrong cause, which sends the reader looking at their own project instead of at the plugin.

How it surfaced. On 2026-08-10, every Cortex hook failed this way from an unrelated repository, repeatedly, before the cause was traced back here. The message pointed at a path that had never been right, so it read as a local problem rather than a plugin one.

A fallback that guarantees a wrong path is not a fallback. It converts a clear configuration error — "this variable is not set" — into a misleading runtime one, and it belongs to the same family as a gate that opens when it cannot decide.

The change

The hooks now refuse and name the missing variable:

if [ -z "${CLAUDE_PLUGIN_ROOT:-}" ]; then
  echo "cortex hook: CLAUDE_PLUGIN_ROOT is unset; refusing to guess the plugin root" >&2
  exit 1
fi
ROOT="$CLAUDE_PLUGIN_ROOT"

Nine occurrences, no other edit. The file was re-parsed as JSON after the change.

Verified both directions on the final state

Unset — refuses, names the variable:

$ eval "$SESSION_END_HOOK_COMMAND" </dev/null
cortex hook: CLAUDE_PLUGIN_ROOT is unset; refusing to guess the plugin root
exit=1

Set — behaviour identical to before the change; the hook reaches the launcher:

$ export CLAUDE_PLUGIN_ROOT="$PWD"; eval "$SESSION_END_HOOK_COMMAND" </dev/null
Original error was: 'numpy._core._multiarray_umath'
exit=1

That trailing numpy failure is pre-existing and unrelated — the same command from origin/main produces it identically in this virtualenv. It is the proof the guard does not change the normal path, not a regression introduced here.

exit 1 on these events is a non-blocking error by the hooks contract, so a misconfigured install now reports the real cause without stopping the session.