js-on-sx: js-neg preserves IEEE-754 negative zero

JS -0 was returning rational integer 0; the (- 0 x) form loses the
sign-of-zero. Switched js-neg to (* -1 (exact->inexact (js-to-number a))),
which produces a float and preserves -0.0. Now 1/(-0) === -Infinity
and Math.asinh(-0) preserves the sign as required by the spec.
built-ins/Math: 41/45 → 42/45. conformance.sh: 148/148.

lib/js/runtime.sx

@@ -1453,7 +1453,7 @@
 
 (define js-pow (fn (a b) (pow (js-to-number a) (js-to-number b))))
 
-(define js-neg (fn (a) (- 0 (js-to-number a))))
+(define js-neg (fn (a) (* -1 (exact->inexact (js-to-number a)))))
 
 (define js-pos (fn (a) (js-to-number a)))
 

lib/js/test262-scoreboard.json

@@ -56,6 +56,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 420.7,
+  "elapsed_seconds": 250.0,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,7 +1,7 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 420.7s
+Wall time: 250.0s
 
 **Total:** 77/99 runnable passed (77.8%). Raw: pass=77 fail=16 skip=1 timeout=6 total=100.
 

plans/js-on-sx.md

@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-07 — **`js-neg` preserves IEEE-754 negative zero.** `-0` was returning `0` (rational integer) because `js-neg` did `(- 0 (js-to-number a))`, which loses sign-of-zero in any arithmetic implementation that follows IEEE 754. Per JS spec, `-0` and `1/-0 === -Infinity` must be observable. Switched to `(* -1 (exact->inexact (js-to-number a)))` so the result is always a float and `-0.0` is preserved. Fixes `Math.asinh(-0)` and other `-0`-sensitive tests; `1/(-0) === -Infinity` now works. built-ins/Math: 41/45 → 42/45. conformance.sh: 148/148.
+
 - 2026-05-07 — **`js-div` coerces divisor to inexact before dividing.** When both operands are SX rationals (e.g. `(js-div 1 0)` from JS-transpiled `1/0` reaching the harness's `_isSameValue` +0/-0 check), SX integer-rational division throws "rational: division by zero" instead of producing JS `Infinity`. Wrapped the divisor in `(exact->inexact ...)` so it's always a float; integer-by-zero now returns `inf` (positive numerator), `-inf` (negative), `nan` (zero numerator), matching JS semantics. Was hitting harness assertion failures even when the test value matched expected. built-ins/Number: 37/50 → 41/50. built-ins/String: 77/99. conformance.sh: 148/148.
 
 - 2026-05-07 — **`js-to-string` throws `TypeError` when both toString and valueOf return non-primitives.** Per ECMA, `String(obj)` (and any string coercion) should throw TypeError when `obj.toString()` and `obj.valueOf()` both return objects. Was returning the literal `"[object Object]"` instead, silently swallowing the spec violation. Replaced the inner `"[object Object]"` fallback with `(raise (js-new-call TypeError (list "Cannot convert object to primitive value")))`. Preserves the outer `"[object Object]"` for the case where there's no `toString` lambda at all. Fixes `S8.12.8_A1`. built-ins/String: 75/99 → 77/99 (canonical, best of three runs; timeout flakiness varies the headline by ±3). conformance.sh: 148/148.