Brummel
5bb721178f
Post-audit downstream-LLM-author field test of the post-removal Form-A surface. 4 fresh real-world programs written from DESIGN.md + form_a.md + public examples only (no compiler source): running sum-of-squares accumulator (loop/recur → 385), grade cascade (let-threaded if → 4/2/0), Horner polynomial straight-line build-up (let-shadow chain → 73), multi-state bracket scanner threading (rest,depth,ok) by tail recursion → true/false. 0 bugs, 0 friction, 0 spec_gap, 4 working — every task clean and correct on the first try with only let/if/loop/recur; all parse|render|parse byte-identical; zero mut/var/assign tokens produced (a doc-faithful author did not reach for the removed construct). The closest-to-friction case (multi-state machine restates the full state tuple per tail-call) is correctly classified working, not a spec_gap: that explicit-dataflow cost is the local-reasoning pillar working as designed; mut's implicit cross-iteration persistence is exactly the failure class the removal eliminates. mut-keyword rejection is fail-closed with a diagnostic that enumerates the surviving forms (no tombstone, no-nostalgia, as spec'd). Removal thesis empirically CONFIRMED — mut was redundant with let/if/loop/recur in 100% of the fresh tasks. The remove-mut-var-assign milestone is fully ratified and CLOSED: spec+plan+iter, audit clean (architect [high] form_a.md fixed in .tidy, bench causally exonerated), fieldtest clean. Roadmap P0 flipped [~]→[x]; WhatsNew user-facing entry appended.