js-on-sx: arrays inherit from Array.prototype on lookup miss

js-get-prop for SX lists fell through to js-undefined for any key
not in its hardcoded method list, so Array.prototype.myprop and
Object.prototype.hasOwnProperty were invisible to arrays.
Switched the fallback to walk Array.prototype via js-dict-get-walk,
which already chains to Object.prototype.
built-ins/Array: 14/45 → 16/45. conformance.sh: 148/148.

lib/js/runtime.sx

@@ -2682,7 +2682,7 @@
             ((= key "copyWithin") (js-array-method obj "copyWithin"))
             ((= key "toReversed") (js-array-method obj "toReversed"))
             ((= key "toSorted") (js-array-method obj "toSorted"))
-            (else js-undefined)))
+            (else (js-dict-get-walk (get Array "prototype") (js-to-string key)))))
         ((= (type-of obj) "string")
           (cond
             ((= key "length") (len obj))

lib/js/test262-scoreboard.json

@@ -1,42 +1,30 @@
 {
   "totals": {
-    "pass": 14,
-    "fail": 25,
-    "skip": 5,
-    "timeout": 6,
+    "pass": 43,
+    "fail": 4,
+    "skip": 0,
+    "timeout": 3,
     "total": 50,
-    "runnable": 45,
-    "pass_rate": 31.1
+    "runnable": 50,
+    "pass_rate": 86.0
   },
   "categories": [
     {
-      "category": "built-ins/Array",
+      "category": "built-ins/Number",
       "total": 50,
-      "pass": 14,
-      "fail": 25,
-      "skip": 5,
-      "timeout": 6,
-      "pass_rate": 31.1,
+      "pass": 43,
+      "fail": 4,
+      "skip": 0,
+      "timeout": 3,
+      "pass_rate": 86.0,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          20
+          4
         ],
         [
           "Timeout",
-          6
-        ],
-        [
-          "TypeError: not a function",
-          2
-        ],
-        [
-          "ReferenceError (undefined symbol)",
-          2
-        ],
-        [
-          "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
-          1
+          3
         ]
       ]
     }
@@ -44,26 +32,14 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      20
+      4
     ],
     [
       "Timeout",
-      6
-    ],
-    [
-      "TypeError: not a function",
-      2
-    ],
-    [
-      "ReferenceError (undefined symbol)",
-      2
-    ],
-    [
-      "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
-      1
+      3
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 132.0,
+  "elapsed_seconds": 71.8,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,30 +1,24 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 132.0s
+Wall time: 71.8s
 
-**Total:** 14/45 runnable passed (31.1%). Raw: pass=14 fail=25 skip=5 timeout=6 total=50.
+**Total:** 43/50 runnable passed (86.0%). Raw: pass=43 fail=4 skip=0 timeout=3 total=50.
 
 ## Top failure modes
 
-- **20x** Test262Error (assertion failed)
-- **6x** Timeout
-- **2x** TypeError: not a function
-- **2x** ReferenceError (undefined symbol)
-- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
+- **4x** Test262Error (assertion failed)
+- **3x** Timeout
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Array | 14 | 25 | 5 | 6 | 50 | 31.1% |
+| built-ins/Number | 43 | 4 | 0 | 3 | 50 | 86.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Array  (14/45 — 31.1%)
+### built-ins/Number  (43/50 — 86.0%)
 
-- **20x** Test262Error (assertion failed)
-- **6x** Timeout
-- **2x** TypeError: not a function
-- **2x** ReferenceError (undefined symbol)
-- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
+- **4x** Test262Error (assertion failed)
+- **3x** Timeout

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 — **Arrays inherit unknown properties from `Array.prototype` (and onwards via `__proto__`).** `Array.prototype.myprop = 42; var x = []; x.myprop` was returning undefined and `x.hasOwnProperty(...)` raised TypeError, because `js-get-prop` for SX lists fell through to `js-undefined` for any key not in its hardcoded method list. Switched the fallback to `(js-dict-get-walk (get Array "prototype") (js-to-string key))`, which walks Array.prototype → (via the recent `__proto__` fallback) Object.prototype. Now custom Array.prototype properties propagate, and `arr.hasOwnProperty` resolves to `Object.prototype.hasOwnProperty`. built-ins/Array: 14/45 → 16/45. conformance.sh: 148/148.
+
 - 2026-05-08 — **Arrays accept numeric-string property keys (`arr["0"]`).** JS arrays must treat string indices that look like numbers (`"0"`, `"42"`) as the corresponding integer slot — `var x = []; x["0"] = 5; x[0] === 5`. `js-get-prop` and `js-list-set!` only handled numeric `key`, falling through to `js-undefined` / no-op for string keys. Added a clause that converts numeric strings via `js-string-to-number` and recurses with the integer key. built-ins/Array: 13/45 → 14/45. conformance.sh: 148/148.
 
 - 2026-05-07 — **JS top-level `var` no longer pollutes SX global env; call args use `js-args` to avoid `list` shadow.** `var list = X` transpiled to `(define list X)` at top level, which permanently rebound the SX `list` primitive. Then any later code (including the runtime itself) calling `(list ...)` got "Not callable: <X>". Two-part fix: (1) wrap the whole transpiled program in `(let () ...)` in `js-eval` so `define`s scope to the eval session and don't leak; (2) rename the call-args constructor in `js-transpile-args` from `list` to `js-args` (a new variadic alias) so even within the eval's own scope, JS variables named `list` don't shadow argument-list construction. Array-literal transpile keeps `list` (lists must be mutable). built-ins/Object: 41/50 → 42/50; Array.from on array-likes now works. conformance.sh: 148/148.