HS add/append: Set dedup, @attr support, when-clause result tracking

- runtime hs-add-to!/hs-append: dedupe on list targets (Set semantics)
- compiler emit-set: set result to X now syncs it too
- compiler append!: handle (local)/(ref) targets via emit-set so scoped
  vars get rebound to the returned list
- parser add/remove: accept bare @attr (not just [@attr])
- parser add-attr: support when-clause → emits add-attr-when
- compiler add-class-when/add-attr-when: collect matched items into
  the-result / it so subsequent "if the result is empty" works

+6 upstream tests in early range (add 13→17, append 10→12).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/js/test262-scoreboard.json

@@ -1,35 +1,76 @@
 {
   "totals": {
-    "pass": 0,
-    "fail": 1,
-    "skip": 0,
-    "timeout": 7,
-    "total": 8,
-    "pass_rate": 0.0
+    "pass": 56,
+    "fail": 230,
+    "skip": 39,
+    "timeout": 2,
+    "total": 327,
+    "runnable": 288,
+    "pass_rate": 19.4
   },
   "categories": [
     {
       "category": "built-ins/Math",
-      "total": 8,
-      "pass": 0,
-      "fail": 1,
-      "skip": 0,
-      "timeout": 7,
-      "pass_rate": 0.0,
+      "total": 327,
+      "pass": 56,
+      "fail": 230,
+      "skip": 39,
+      "timeout": 2,
+      "pass_rate": 19.4,
       "top_failures": [
+        [
+          "Test262Error (assertion failed)",
+          83
+        ],
+        [
+          "ReferenceError (undefined symbol)",
+          62
+        ],
+        [
+          "TypeError: not a function",
+          46
+        ],
         [
           "SyntaxError (parse/unsupported syntax)",
-          1
+          35
+        ],
+        [
+          "Unhandled: Unexpected token: op '++'\\",
+          3
         ]
       ]
     }
   ],
   "top_failure_modes": [
+    [
+      "Test262Error (assertion failed)",
+      83
+    ],
+    [
+      "ReferenceError (undefined symbol)",
+      62
+    ],
+    [
+      "TypeError: not a function",
+      46
+    ],
     [
       "SyntaxError (parse/unsupported syntax)",
+      35
+    ],
+    [
+      "Unhandled: Unexpected token: op '++'\\",
+      3
+    ],
+    [
+      "Timeout",
+      2
+    ],
+    [
+      "Unhandled: Not callable: {:random <js-math-random()> :floor <js-math-fl",
       1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 40.1
+  "elapsed_seconds": 185.3
 }

lib/js/test262-scoreboard.md

@@ -1,21 +1,32 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
+Wall time: 185.3s
 
-**Total:** 0/8 passed (0.0%), 1 failed, 0 skipped, 7 timeouts.
+**Total:** 56/288 runnable passed (19.4%). Raw: pass=56 fail=230 skip=39 timeout=2 total=327.
 
 ## Top failure modes
 
-- **1x** SyntaxError (parse/unsupported syntax)
+- **83x** Test262Error (assertion failed)
+- **62x** ReferenceError (undefined symbol)
+- **46x** TypeError: not a function
+- **35x** SyntaxError (parse/unsupported syntax)
+- **3x** Unhandled: Unexpected token: op '++'\
+- **2x** Timeout
+- **1x** Unhandled: Not callable: {:random <js-math-random()> :floor <js-math-fl
 
-## Categories (worst pass-rate first)
+## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Math | 0 | 1 | 0 | 7 | 8 | 0.0% |
+| built-ins/Math | 56 | 230 | 39 | 2 | 327 | 19.4% |
 
-## Per-category top failures
+## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Math
+### built-ins/Math  (56/288 — 19.4%)
 
-- **1x** SyntaxError (parse/unsupported syntax)
+- **83x** Test262Error (assertion failed)
+- **62x** ReferenceError (undefined symbol)
+- **46x** TypeError: not a function
+- **35x** SyntaxError (parse/unsupported syntax)
+- **3x** Unhandled: Unexpected token: op '++'\