js-on-sx: fn.toString honours Function.prototype.toString overrides

Two hardcoded paths returned the native marker regardless of user
override: js-invoke-function-method and the lambda branch of
js-to-string. Both now look up Function.prototype.toString via
js-dict-get-walk and invoke it on the function, falling back to
the native marker only if no override exists.
built-ins/String: 84/99 → 85/99. conformance.sh: 148/148.

lib/js/runtime.sx

@@ -306,7 +306,13 @@
           (fn
             (&rest more)
             (js-call-with-this this-arg recv (js-list-concat bound more)))))
-      ((= key "toString") "function () { [native code] }")
+      ((= key "toString")
+        (let
+          ((override (js-dict-get-walk (get js-function-global "prototype") "toString")))
+          (if
+            (= (type-of override) "lambda")
+            (js-call-with-this recv override args)
+            "function () { [native code] }")))
       ((= key "name") (js-extract-fn-name recv))
       ((= key "length") (js-fn-length recv))
       (else :js-undefined))))
@@ -1393,7 +1399,18 @@
                           "[object Object]"))
                       (js-to-string result)))
                   "[object Object]"))))
-          (if (= (type-of v) "list") (js-list-join v ",") (str v)))))))
+          (cond
+            ((= (type-of v) "list") (js-list-join v ","))
+            ((js-function? v)
+              (let
+                ((tostr-fn (js-dict-get-walk (get js-function-global "prototype") "toString")))
+                (if
+                  (= (type-of tostr-fn) "lambda")
+                  (let
+                    ((result (js-call-with-this v tostr-fn ())))
+                    (if (= (type-of result) "string") result "function () { [native code] }"))
+                  "function () { [native code] }")))
+            (else (str v))))))))
 
 (define
   js-template-concat

lib/js/test262-scoreboard.json

@@ -1,26 +1,26 @@
 {
   "totals": {
-    "pass": 84,
-    "fail": 12,
+    "pass": 85,
+    "fail": 11,
     "skip": 1,
     "timeout": 3,
     "total": 100,
     "runnable": 99,
-    "pass_rate": 84.8
+    "pass_rate": 85.9
   },
   "categories": [
     {
       "category": "built-ins/String",
       "total": 100,
-      "pass": 84,
-      "fail": 12,
+      "pass": 85,
+      "fail": 11,
       "skip": 1,
       "timeout": 3,
-      "pass_rate": 84.8,
+      "pass_rate": 85.9,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          10
+          9
         ],
         [
           "Timeout",
@@ -40,7 +40,7 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      10
+      9
     ],
     [
       "Timeout",
@@ -56,6 +56,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 192.4,
+  "elapsed_seconds": 182.4,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,13 +1,13 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 192.4s
+Wall time: 182.4s
 
-**Total:** 84/99 runnable passed (84.8%). Raw: pass=84 fail=12 skip=1 timeout=3 total=100.
+**Total:** 85/99 runnable passed (85.9%). Raw: pass=85 fail=11 skip=1 timeout=3 total=100.
 
 ## Top failure modes
 
-- **10x** Test262Error (assertion failed)
+- **9x** Test262Error (assertion failed)
 - **3x** Timeout
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)
@@ -16,13 +16,13 @@ Wall time: 192.4s
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 84 | 12 | 1 | 3 | 100 | 84.8% |
+| built-ins/String | 85 | 11 | 1 | 3 | 100 | 85.9% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/String  (84/99 — 84.8%)
+### built-ins/String  (85/99 — 85.9%)
 
-- **10x** Test262Error (assertion failed)
+- **9x** Test262Error (assertion failed)
 - **3x** Timeout
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)

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.
 
+- 2026-05-08 — **`fn.toString()` and `String(fn)` honour `Function.prototype.toString` overrides.** Two hardcoded paths returned `"function () { [native code] }"` regardless of any user override: the function-method dispatch in `js-invoke-function-method`, and the lambda branch of `js-to-string`. Both now look up `Function.prototype.toString` via `js-dict-get-walk` and invoke it on the function (`recv`/`v`) when available, falling back to the native marker only if no override exists. Now `Function.prototype.toString = ...; (function(){}).toString()` returns the override, and `new String(fn)` stores the override result. built-ins/String: 84/99 → 85/99. conformance.sh: 148/148.
+
 - 2026-05-08 — **Native prototypes carry the wrapped primitive marker.** Per ES, `Boolean.prototype` is a Boolean wrapper around `false`, `Number.prototype` wraps `0`, `String.prototype` wraps `""`. So `Boolean.prototype == false` (loose-eq unwraps), `Object.prototype.toString.call(Number.prototype) === "[object Number]"`, etc. Set `__js_boolean_value__: false` / `__js_number_value__: 0` / `__js_string_value__: ""` on the respective prototypes in the post-init block. built-ins/Boolean: 23/27 → 24/27, String: 80/99 → 84/99. conformance.sh: 148/148.
 
 - 2026-05-08 — **`js-to-number` throws TypeError when valueOf+toString both return non-primitive.** Mirrors the earlier `js-to-string` fix. Per spec, `Number(obj)` must throw if `ToPrimitive` cannot extract a primitive. Was returning `NaN` silently. Replaced the inner `(js-nan-value)` fallback with `(raise (js-new-call TypeError ...))`. built-ins/Number: 45/50 → 46/50. conformance.sh: 148/148.