diff --git a/lib/lua/runtime.sx b/lib/lua/runtime.sx
index abd7a3d7..090415d3 100644
--- a/lib/lua/runtime.sx
+++ b/lib/lua/runtime.sx
@@ -1591,3 +1591,21 @@
 
 ;; T — debug/testC placeholder for tests that check it conditionally
 (define T nil)
+
+;; Build Lua 5.0-style `arg` table: array + .n counter, skipping leading explicit params.
+(define
+  lua-varargs-arg-table
+  (fn (args skip)
+    (let ((t {}) (n 0))
+      (begin
+        (define
+          va-build
+          (fn (i)
+            (when (< i (len args))
+              (begin
+                (set! n (+ n 1))
+                (dict-set! t (str n) (nth args i))
+                (va-build (+ i 1))))))
+        (va-build skip)
+        (dict-set! t "n" n)
+        t))))
diff --git a/lib/lua/scoreboard.json b/lib/lua/scoreboard.json
index 558f4eb2..314ffd65 100644
--- a/lib/lua/scoreboard.json
+++ b/lib/lua/scoreboard.json
@@ -39,7 +39,7 @@
       "name": "attrib.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 7069
+      "ms": 7512
     },
     {
       "name": "big.lua",
@@ -51,7 +51,7 @@
       "name": "calls.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 5059
+      "ms": 5982
     },
     {
       "name": "checktable.lua",
@@ -63,7 +63,7 @@
       "name": "closure.lua",
       "status": "timeout",
       "reason": "per-test timeout",
-      "ms": 8008
+      "ms": 8007
     },
     {
       "name": "code.lua",
@@ -75,7 +75,7 @@
       "name": "constructs.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 4593
+      "ms": 5319
     },
     {
       "name": "db.lua",
@@ -87,13 +87,13 @@
       "name": "errors.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 3390
+      "ms": 3803
     },
     {
       "name": "events.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 7477
+      "ms": 7620
     },
     {
       "name": "files.lua",
@@ -111,13 +111,13 @@
       "name": "literals.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 1883
+      "ms": 1927
     },
     {
       "name": "locals.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: attempt to call non-functio",
-      "ms": 1642
+      "ms": 1702
     },
     {
       "name": "main.lua",
@@ -129,43 +129,43 @@
       "name": "math.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 4194
+      "ms": 4183
     },
     {
       "name": "nextvar.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 6779
+      "ms": 7853
     },
     {
       "name": "pm.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 5731
+      "ms": 6268
     },
     {
       "name": "sort.lua",
       "status": "timeout",
       "reason": "per-test timeout",
-      "ms": 8008
+      "ms": 8007
     },
     {
       "name": "strings.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 3935
+      "ms": 4020
     },
     {
       "name": "vararg.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 2273
+      "ms": 2349
     },
     {
       "name": "verybig.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: attempt to call non-functio",
-      "ms": 564
+      "ms": 579
     }
   ]
 }
\ No newline at end of file
diff --git a/lib/lua/scoreboard.md b/lib/lua/scoreboard.md
index b03a2697..db21961e 100644
--- a/lib/lua/scoreboard.md
+++ b/lib/lua/scoreboard.md
@@ -15,25 +15,25 @@ fail=13 timeout=3 skip=8 total=24
 |---|---|---|---:|
 | all.lua | skip | driver uses dofile to chain other tests | 0 |
 | api.lua | skip | requires testC (C debug library) | 0 |
-| attrib.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7069 |
+| attrib.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7512 |
 | big.lua | timeout | per-test timeout | 8007 |
-| calls.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 5059 |
+| calls.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 5982 |
 | checktable.lua | skip | internal debug helpers | 0 |
-| closure.lua | timeout | per-test timeout | 8008 |
+| closure.lua | timeout | per-test timeout | 8007 |
 | code.lua | skip | bytecode inspection via debug library | 0 |
-| constructs.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4593 |
+| constructs.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 5319 |
 | db.lua | skip | debug library | 0 |
-| errors.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 3390 |
-| events.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7477 |
+| errors.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 3803 |
+| events.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7620 |
 | files.lua | skip | io library | 0 |
 | gc.lua | skip | collectgarbage / finalisers | 0 |
-| literals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 1883 |
-| locals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 1642 |
+| literals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 1927 |
+| locals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 1702 |
 | main.lua | skip | standalone interpreter driver | 0 |
-| math.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4194 |
-| nextvar.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 6779 |
-| pm.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 5731 |
-| sort.lua | timeout | per-test timeout | 8008 |
-| strings.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 3935 |
-| vararg.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 2273 |
-| verybig.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 564 |
+| math.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4183 |
+| nextvar.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7853 |
+| pm.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 6268 |
+| sort.lua | timeout | per-test timeout | 8007 |
+| strings.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4020 |
+| vararg.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 2349 |
+| verybig.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 579 |
diff --git a/lib/lua/test.sh b/lib/lua/test.sh
index cadc2c3f..cd2b70a0 100755
--- a/lib/lua/test.sh
+++ b/lib/lua/test.sh
@@ -916,6 +916,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1812)
 (eval "(lua-eval-ast \"local x = 10 if false then elseif true then local x = 99 end return x\")")
 
+;; ── Lua 5.0-style `arg` table in vararg functions ─────────────
+(epoch 1820)
+(eval "(lua-eval-ast \"function f(a, ...) return arg.n end return f({}, 1, 2, 3)\")")
+(epoch 1821)
+(eval "(lua-eval-ast \"function f(a, ...) return arg[1] + arg[2] + arg[3] end return f({}, 10, 20, 30)\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1381,6 +1387,10 @@ check 1810 "if then local shadows"          '10'
 check 1811 "else local shadows"             '10'
 check 1812 "elseif local shadows"           '10'
 
+# ── Lua 5.0-style `arg` table in vararg functions ─────────────
+check 1820 "arg.n in vararg fn"             '3'
+check 1821 "arg[i] access"                  '60'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL Lua-on-SX tests passed"
diff --git a/lib/lua/transpile.sx b/lib/lua/transpile.sx
index f7feaefe..8c5e39a4 100644
--- a/lib/lua/transpile.sx
+++ b/lib/lua/transpile.sx
@@ -180,6 +180,13 @@
       (make-symbol "__varargs")
       (list (make-symbol "lua-varargs") (make-symbol "__args") n))))
 
+(define
+  lua-tx-function-arg-binding
+  (fn (n)
+    (list
+      (make-symbol "arg")
+      (list (make-symbol "lua-varargs-arg-table") (make-symbol "__args") n))))
+
 (define
   lua-tx-function
   (fn
@@ -200,7 +207,10 @@
             (let
               ((all-bindings
                  (if is-vararg
-                     (append bindings (list (lua-tx-function-varargs-binding (len params))))
+                     (append bindings
+                       (list
+                         (lua-tx-function-varargs-binding (len params))
+                         (lua-tx-function-arg-binding (len params))))
                      bindings)))
               (list
                 (make-symbol "fn")
diff --git a/plans/lua-on-sx.md b/plans/lua-on-sx.md
index feb0a92a..d4886605 100644
--- a/plans/lua-on-sx.md
+++ b/plans/lua-on-sx.md
@@ -82,6 +82,7 @@ Each item: implement → tests → tick box → update progress log.
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-24: lua: scoreboard iteration — Lua 5.0-style `arg` auto-binding inside vararg functions (some PUC-Rio tests still rely on it). `lua-varargs-arg-table` builds `{1=v1, 2=v2, …, n=count}`; transpile adds `arg` binding alongside `__varargs` when `is-vararg`. Diagnosis done with assert-counter instrumentation — literals.lua fails at #4 (long-string NL rule), vararg.lua was at #2 (arg table — FIXED), attrib.lua at #9, locals.lua now past asserts into call-non-fn. 360 tests.
 - 2026-04-24: lua: scoreboard iteration — **`loadstring` scoping**. Temporarily instrumented `lua-assert` with a counter, found `locals.lua` fails at assertion #5: `loadstring('local a = {}')() → assert(type(a) ~= 'table')`. The loadstring'd code's `local a` was leaking to outer scope because `lua-eval-ast` ran at top-level. Fixed by transpiling once and wrapping the AST in `(let () …)` before `eval-expr`.
 - 2026-04-24: lua: scoreboard iteration — **`if`/`else`/`elseif` body scoping** (latent bug). `else local x = 99` was leaking to enclosing scope. Wrap all three branches in `(let () …)` via `lua-tx-if-body`. 358 tests.
 - 2026-04-24: lua: scoreboard iteration — **`do`-block proper scoping**. Was transpiling `do ... end` to a raw `lua-tx` pass-through, so `define`s inside leaked to the enclosing scope (`do local i = 100 end` overwrote outer `i`). Now wraps in `(let () body)` for proper lexical isolation. 355 tests, +2 scoping tests.