Extends the fixpoint beyond the compiler image to the whole emitted system.
emit-image.ss now handles macros (defmacro -> bare expander fn + def-var! +
mark-macro!) and re-emits the clojure.core prelude (all tiers + stdlib) on Chez
via jolt-emit-prelude; driver's emit-image-on-chez takes an emit-fn arg.
The prelude converges at pstage3==pstage4 (one stage later than the compiler's
stage2==stage3) because macro expanders bake an auto-gensym id at emit time, so a
Janet-emitted macro carries a different id than a Chez-emitted one — only once
both stages load a Chez-emitted prelude does it stabilize.
fixpoint-test now proves: compiler stage2==stage3, prelude pstage3==pstage4, and
the fully Chez-emitted system (Chez prelude + Chez image, no Janet artifact in the
loop) compiles+runs real cases. 10/10.
The zero-Janet spine proves the on-Chez analyzer/emitter compile arbitrary
Clojure faithfully. This proves the stronger property: the on-Chez compiler
reproduces itself. emit-image.ss re-emits the compiler sources (jolt.ir +
jolt.analyzer + jolt.backend-scheme) ON CHEZ via the loaded image; feeding it
stage1 (the Janet cross-compile) yields stage2, feeding stage2 yields stage3.
stage2 and stage3 are byte-for-byte identical, and stage2 is a working compiler
(real cases compile+run through it). stage1 differs from stage2 only in gensym
numbering, so the fixpoint is stage2==stage3.
driver: emit-image-on-chez / program-emit-image spawn a fresh chez per stage
(clean gensym state). test/chez/fixpoint-test.janet gates it (skips without chez).
