Revise the epic's direction from a minimal Janet shim to ripping Janet
out entirely — Chez becomes the sole substrate. The missing spine: the
compiler pipeline itself only runs on Janet today (the analyzer executes
on the Janet host; the IR->Scheme emitter is host/chez/emit.janet). Phase
3 is re-scoped to self-host the compiler on Chez (emitter -> Clojure
jolt.backend-scheme, reader -> jolt-core, compile-from-source bootstrap
fixpoint). Phase 5 becomes a hard delete of both src/jolt/*.janet and
host/chez/*.janet. Sequencing: core parity first, then self-host, then
delete.
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