Panic/recover builtins + per-frame __go-panic-cell of shape
(STATE V). Body panic flips cell :none→:raised BEFORE defers drain
so recover() can find it. recover() walks env chain past shadowing
cells to the outermost :raised one — flips it :recovered, returns V.
Frame exit checks cell: :recovered → return clean; :raised →
propagate (:go-panic V).
6 tests: uncaught-from-program, panic-from-fn, defer-recover-swallow,
recover-captures-via-channel, propagation-through-no-defer-chain,
middle-frame-catches-deeper-panic.
Shape: panic cell is a frame-attached out-of-band channel that
survives function boundaries via env-chain walk. Same primitive
slots into the scheduler kit's termination-record + cleanup-with-
error-context hook. Maps cleanly to Erlang try/catch/after.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
giles
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