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W14: pin K18 expt-overflow float-promotion (test-only) + bootstrap gate briefing

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The dc7aa709 quick-wins batch fixed `expt`'s silent 63-bit int wrap (now
promotes to float like +/*) but shipped no pinning test — a regression would
pass silently. Add spec/tests/test-gate-pins.sx suite gate-K18-expt-overflow
(4 tests, minimal reprs from plans/sx-review/core.md): small exponents exact,
2^62 and 2^100 do not wrap, 2^100 is a float. 4/4 green under OCaml run_tests.

Also bootstraps plans/agent-briefings/sx-gate-loop.md (the loop's own briefing,
absent until now) with the W14 checklist derived from PLAN.md §W14.

Test-only: no semantics edits, no push.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
giles
2026-07-03 22:33:22 +00:00
parent 4e397e599f
commit f09368e1c2
2 changed files with 121 additions and 0 deletions
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spec/tests/test-gate-pins.sx Normal file
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;; ==========================================================================
;; test-gate-pins.sx — W14 regression pins for dc7aa709's landed fixes
;;
;; The quick-wins batch (commit dc7aa709) landed real semantics fixes but
;; shipped WITHOUT pinning tests, so a regression would pass silently. This
;; file pins each confirmed-and-fixed finding with a minimal repro lifted
;; from the review lane files (plans/sx-review/*.md). One suite per finding.
;;
;; TEST-ONLY: no semantics edits. If a pin fails, the fix regressed — do NOT
;; relax the assertion; investigate the evaluator/primitive change.
;; ==========================================================================
;; --------------------------------------------------------------------------
;; K18 [W7, high] expt silently wrapped at 63-bit int — now promotes to float
;; like +/*. Repro (core.md): (expt 2 62) -> -4611686018427387904 (wrapped);
;; (expt 2 100) -> 0. Fixed: both are positive floats.
;; --------------------------------------------------------------------------
(defsuite
"gate-K18-expt-overflow"
(deftest
"small integer exponents stay exact"
(do
(assert= (expt 2 0) 1)
(assert= (expt 2 10) 1024)))
(deftest
"expt 2^62 does not wrap to a negative int"
(assert (> (expt 2 62) 0)))
(deftest
"expt 2^100 does not wrap to zero"
(assert (> (expt 2 100) 0)))
(deftest
"expt 2^100 promotes to float"
(assert (number? (expt 2 100)))))