cl-debugger-hook global (nil = default), cl-invoke-debugger walks the hook,
cl-error-with-debugger routes unhandled errors through the hook, and
make-policy-debugger builds a hook from a (fn (condition restarts) name)
policy function. Tests: hook receives condition, policy selects use-zero/abort
restarts, compute-restarts visible inside hook, handler wins before hook fires,
infinite-recursion guard. Wired into test.sh program suite runner.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
