diff --git a/lib/lua/runtime.sx b/lib/lua/runtime.sx
index c88dbcce..5efbf147 100644
--- a/lib/lua/runtime.sx
+++ b/lib/lua/runtime.sx
@@ -59,28 +59,29 @@
 (define
   lua-arith
   (fn
-    (mm op a b)
-    (cond
-      ((and (= (type-of a) "number") (= (type-of b) "number"))
-        (lua-num-op op a b))
-      ((and
-         (or (= (type-of a) "number") (= (type-of a) "string"))
-         (or (= (type-of b) "number") (= (type-of b) "string"))
-         (not (= (lua-to-number a) nil))
-         (not (= (lua-to-number b) nil)))
-        (lua-num-op op a b))
-      (else
-        (let
-          ((m (lua-get-mm a mm)))
-          (cond
-            ((not (= m nil)) (lua-first (m a b)))
-            (else
-              (let
-                ((m2 (lua-get-mm b mm)))
-                (if
-                  (not (= m2 nil))
-                  (lua-first (m2 a b))
-                  (error (str "lua: arith on " (type-of a) " " op " " (type-of b))))))))))))
+    (mm op a-in b-in)
+    (let ((a (lua-first a-in)) (b (lua-first b-in)))
+      (cond
+        ((and (= (type-of a) "number") (= (type-of b) "number"))
+          (lua-num-op op a b))
+        ((and
+           (or (= (type-of a) "number") (= (type-of a) "string"))
+           (or (= (type-of b) "number") (= (type-of b) "string"))
+           (not (= (lua-to-number a) nil))
+           (not (= (lua-to-number b) nil)))
+          (lua-num-op op a b))
+        (else
+          (let
+            ((m (lua-get-mm a mm)))
+            (cond
+              ((not (= m nil)) (lua-first (m a b)))
+              (else
+                (let
+                  ((m2 (lua-get-mm b mm)))
+                  (if
+                    (not (= m2 nil))
+                    (lua-first (m2 a b))
+                    (error (str "lua: arith on " (type-of a) " " op " " (type-of b)))))))))))))
 
 (define lua-add (fn (a b) (lua-arith "__add" "+" a b)))
 
@@ -116,33 +117,35 @@
 (define
   lua-concat-coerce
   (fn
-    (v)
-    (cond
-      ((= (type-of v) "string") v)
-      ((= (type-of v) "number") (str v))
-      (else (error (str "lua: cannot concat " v))))))
+    (v-in)
+    (let ((v (lua-first v-in)))
+      (cond
+        ((= (type-of v) "string") v)
+        ((= (type-of v) "number") (str v))
+        (else (error (str "lua: cannot concat " v)))))))
 
 (define
   lua-concat
   (fn
-    (a b)
-    (cond
-      ((and
-         (or (= (type-of a) "string") (= (type-of a) "number"))
-         (or (= (type-of b) "string") (= (type-of b) "number")))
-        (str (lua-concat-coerce a) (lua-concat-coerce b)))
-      (else
-        (let
-          ((m (lua-get-mm a "__concat")))
-          (cond
-            ((not (= m nil)) (lua-first (m a b)))
-            (else
-              (let
-                ((m2 (lua-get-mm b "__concat")))
-                (if
-                  (not (= m2 nil))
-                  (lua-first (m2 a b))
-                  (error (str "lua: concat on " (type-of a) " and " (type-of b))))))))))))
+    (a-in b-in)
+    (let ((a (lua-first a-in)) (b (lua-first b-in)))
+      (cond
+        ((and
+           (or (= (type-of a) "string") (= (type-of a) "number"))
+           (or (= (type-of b) "string") (= (type-of b) "number")))
+          (str (lua-concat-coerce a) (lua-concat-coerce b)))
+        (else
+          (let
+            ((m (lua-get-mm a "__concat")))
+            (cond
+              ((not (= m nil)) (lua-first (m a b)))
+              (else
+                (let
+                  ((m2 (lua-get-mm b "__concat")))
+                  (if
+                    (not (= m2 nil))
+                    (lua-first (m2 a b))
+                    (error (str "lua: concat on " (type-of a) " and " (type-of b)))))))))))))
 
 (define
   lua-eq
@@ -1646,3 +1649,6 @@
 (define
   lua-return-value
   (fn (e) (if (> (len e) 1) (nth e 1) nil)))
+
+(define lua-break-sentinel?
+  (fn (e) (and (= (type-of e) "list") (> (len e) 0) (= (first e) (quote lua-brk)))))
diff --git a/lib/lua/scoreboard.json b/lib/lua/scoreboard.json
index 4bbeb235..caa7b7d5 100644
--- a/lib/lua/scoreboard.json
+++ b/lib/lua/scoreboard.json
@@ -1,8 +1,8 @@
 {
   "totals": {
     "pass": 0,
-    "fail": 13,
-    "timeout": 3,
+    "fail": 12,
+    "timeout": 4,
     "skip": 8,
     "total": 24,
     "runnable": 16,
@@ -15,15 +15,11 @@
     ],
     [
       "timeout",
-      3
+      4
     ],
     [
       "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: attempt to call non-functio",
       2
-    ],
-    [
-      "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: concat on list and string\\\\",
-      1
     ]
   ],
   "results": [
@@ -43,19 +39,19 @@
       "name": "attrib.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 6225
+      "ms": 6183
     },
     {
       "name": "big.lua",
       "status": "timeout",
       "reason": "per-test timeout",
-      "ms": 8008
+      "ms": 8007
     },
     {
       "name": "calls.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 5175
+      "ms": 4986
     },
     {
       "name": "checktable.lua",
@@ -67,7 +63,7 @@
       "name": "closure.lua",
       "status": "timeout",
       "reason": "per-test timeout",
-      "ms": 8007
+      "ms": 8008
     },
     {
       "name": "code.lua",
@@ -77,9 +73,9 @@
     },
     {
       "name": "constructs.lua",
-      "status": "fail",
-      "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: concat on list and string\\\\",
-      "ms": 4874
+      "status": "timeout",
+      "reason": "per-test timeout",
+      "ms": 8005
     },
     {
       "name": "db.lua",
@@ -91,13 +87,13 @@
       "name": "errors.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 3289
+      "ms": 3253
     },
     {
       "name": "events.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 7546
+      "ms": 7283
     },
     {
       "name": "files.lua",
@@ -115,13 +111,13 @@
       "name": "literals.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 1888
+      "ms": 1857
     },
     {
       "name": "locals.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: attempt to call non-functio",
-      "ms": 1721
+      "ms": 1726
     },
     {
       "name": "main.lua",
@@ -133,43 +129,43 @@
       "name": "math.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 4231
+      "ms": 4173
     },
     {
       "name": "nextvar.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 7290
+      "ms": 7128
     },
     {
       "name": "pm.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 6155
+      "ms": 6098
     },
     {
       "name": "sort.lua",
       "status": "timeout",
       "reason": "per-test timeout",
-      "ms": 8006
+      "ms": 8008
     },
     {
       "name": "strings.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 4215
+      "ms": 4137
     },
     {
       "name": "vararg.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"assertion failed!\\\\\\\"\\",
-      "ms": 2288
+      "ms": 2264
     },
     {
       "name": "verybig.lua",
       "status": "fail",
       "reason": "other: Unhandled exception: \\\"Unhandled exception: \\\\\\\"lua: attempt to call non-functio",
-      "ms": 622
+      "ms": 575
     }
   ]
 }
\ No newline at end of file
diff --git a/lib/lua/scoreboard.md b/lib/lua/scoreboard.md
index f04e00bb..44bbfda4 100644
--- a/lib/lua/scoreboard.md
+++ b/lib/lua/scoreboard.md
@@ -1,14 +1,13 @@
 # Lua-on-SX conformance scoreboard
 
 **Pass rate:** 0/16 runnable (0.0%)
-fail=13 timeout=3 skip=8 total=24
+fail=12 timeout=4 skip=8 total=24
 
 ## Top failure modes
 
 - **10x** other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\
-- **3x** timeout
+- **4x** timeout
 - **2x** other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio
-- **1x** other: Unhandled exception: \"Unhandled exception: \\\"lua: concat on list and string\\
 
 ## Per-test results
 
@@ -16,25 +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!\\\"\ | 6225 |
-| big.lua | timeout | per-test timeout | 8008 |
-| calls.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 5175 |
+| attrib.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 6183 |
+| big.lua | timeout | per-test timeout | 8007 |
+| calls.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4986 |
 | checktable.lua | skip | internal debug helpers | 0 |
-| closure.lua | timeout | per-test timeout | 8007 |
+| closure.lua | timeout | per-test timeout | 8008 |
 | code.lua | skip | bytecode inspection via debug library | 0 |
-| constructs.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: concat on list and string\\ | 4874 |
+| constructs.lua | timeout | per-test timeout | 8005 |
 | db.lua | skip | debug library | 0 |
-| errors.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 3289 |
-| events.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7546 |
+| errors.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 3253 |
+| events.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7283 |
 | files.lua | skip | io library | 0 |
 | gc.lua | skip | collectgarbage / finalisers | 0 |
-| literals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 1888 |
-| locals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 1721 |
+| literals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 1857 |
+| locals.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 1726 |
 | main.lua | skip | standalone interpreter driver | 0 |
-| math.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4231 |
-| nextvar.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7290 |
-| pm.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 6155 |
-| sort.lua | timeout | per-test timeout | 8006 |
-| strings.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4215 |
-| vararg.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 2288 |
-| verybig.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 622 |
+| math.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4173 |
+| nextvar.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 7128 |
+| pm.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 6098 |
+| sort.lua | timeout | per-test timeout | 8008 |
+| strings.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 4137 |
+| vararg.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"assertion failed!\\\"\ | 2264 |
+| verybig.lua | fail | other: Unhandled exception: \"Unhandled exception: \\\"lua: attempt to call non-functio | 575 |
diff --git a/lib/lua/test.sh b/lib/lua/test.sh
index d4f58133..8b427201 100755
--- a/lib/lua/test.sh
+++ b/lib/lua/test.sh
@@ -944,6 +944,16 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1852)
 (eval "(lua-eval-ast \"function f(i) if type(i) ~= \\\"number\\\" then return i, \\\"jojo\\\" end if i > 0 then return i, f(i-1) end end local a, b = f(3) return a\")")
 
+;; ── break via sentinel (escapes while/for-num/for-in/repeat) ──
+(epoch 1860)
+(eval "(lua-eval-ast \"local i = 0 while true do i = i + 1 if i >= 5 then break end end return i\")")
+(epoch 1861)
+(eval "(lua-eval-ast \"local s = 0 for i = 1, 100 do if i > 10 then break end s = s + i end return s\")")
+(epoch 1862)
+(eval "(lua-eval-ast \"local t = {10, 20, 99, 40} local s = 0 for i, v in ipairs(t) do if v == 99 then break end s = s + v end return s\")")
+(epoch 1863)
+(eval "(lua-eval-ast \"local i = 0 repeat i = i + 1 if i >= 3 then break end until false return i\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1427,6 +1437,12 @@ check 1850 "early return negative path"     '-1'
 check 1851 "non-early return path"          '14'
 check 1852 "nested early-return recursion"  '3'
 
+# ── break via sentinel ───────────────────────────────────────
+check 1860 "break in while"                 '5'
+check 1861 "break in for-num"               '55'
+check 1862 "break in for-in"                '30'
+check 1863 "break in repeat"                '3'
+
 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 c06824e1..ab7c60fa 100644
--- a/lib/lua/transpile.sx
+++ b/lib/lua/transpile.sx
@@ -1,3 +1,17 @@
+(define
+  lua-tx-loop-guard
+  (fn (body-sx)
+    (list
+      (make-symbol "guard")
+      (list (make-symbol "e")
+        (list
+          (list (make-symbol "lua-break-sentinel?") (make-symbol "e"))
+          nil)
+        (list
+          (make-symbol "else")
+          (list (make-symbol "raise") (make-symbol "e"))))
+      body-sx)))
+
 (define
   lua-tx
   (fn
@@ -36,7 +50,7 @@
       ((= tag (quote lua-for-num)) (lua-tx-for-num node))
       ((= tag (quote lua-for-in)) (lua-tx-for-in node))
       ((= tag (quote lua-do)) (lua-tx-do node))
-      ((= tag (quote lua-break)) (quote lua-break-marker))
+      ((= tag (quote lua-break)) (list (make-symbol "raise") (list (make-symbol "list") (list (make-symbol "quote") (make-symbol "lua-brk")))))
       ((= tag (quote lua-return)) (lua-tx-return node))
       ((= tag (quote lua-call-stmt)) (lua-tx (nth node 1)))
       ((= tag (quote lua-local-function)) (lua-tx-local-function node))
@@ -392,7 +406,7 @@
                 (make-symbol "begin")
                 body
                 (list (make-symbol "_while_loop"))))))
-        (list (make-symbol "_while_loop"))))))
+        (lua-tx-loop-guard (list (make-symbol "_while_loop")))))))
 
 (define
   lua-tx-repeat
@@ -418,7 +432,7 @@
                   (make-symbol "not")
                   (list (make-symbol "lua-truthy?") cnd))
                 (list (make-symbol "_repeat_loop"))))))
-        (list (make-symbol "_repeat_loop"))))))
+        (lua-tx-loop-guard (list (make-symbol "_repeat_loop")))))))
 
 (define
   lua-tx-for-num
@@ -462,7 +476,7 @@
                       (make-symbol name)
                       (make-symbol "_for_step")))
                   (list (make-symbol "_for_loop"))))))
-          (list (make-symbol "_for_loop")))))))
+          (lua-tx-loop-guard (list (make-symbol "_for_loop"))))))))
 
 (define lua-tx-do (fn (node) (list (make-symbol "let") (list) (lua-tx (nth node 1)))))
 
@@ -704,4 +718,4 @@
                       (make-symbol "fn")
                       (list)
                       (lua-tx-for-in-loop-body names body f-sym s-sym v-sym rets-sym loop-sym first-name)))
-                  (list loop-sym))))))))))
+                  (lua-tx-loop-guard (list loop-sym)))))))))))
diff --git a/plans/lua-on-sx.md b/plans/lua-on-sx.md
index 4a6da9fd..72c5946f 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 — **proper `break` via guard+raise sentinel** (`lua-brk`) + auto-first multi-values in arith/concat. Loop break dispatch was previously a no-op (emitted bare `'lua-break-marker` symbol that nothing caught); converted to raise+catch pattern, wrapping the OUTER invocation of `_while_loop`/`_for_loop`/`_repeat_loop`/`__for_loop` in a break-guard (wrapping body doesn't work — break would just be caught and loop keeps recursing). Also `lua-arith`/`lua-concat`/`lua-concat-coerce` now `lua-first` their operands so multi-returns auto-truncate at scalar boundaries. 372/372 green (+4 break tests). Scoreboard: 10×assert / 4×timeout / 2×call-non-fn (no more undef-symbol or compare-incompat).
 - 2026-04-24: lua: scoreboard iteration — **proper early-return via guard+raise sentinel**. Fixes long-logged limitation: `if cond then return X end ...rest` now exits the enclosing function; `rest` is skipped. `lua-tx-return` raises `(list 'lua-ret value)`; every function body and the top-level chunk + loadstring'd chunks wrap in a guard that catches the sentinel and returns its value. Eliminates "compare incompatible types" from constructs.lua (past line 40). 368/368 green (+3 early-return tests).
 - 2026-04-24: lua: scoreboard iteration — **unary-minus / `^` precedence fix**. Per Lua spec, `^` binds tighter than unary `-`, so `-2^2` should parse as `-(2^2) = -4`, not `(-2)^2 = 4`. My parser recursed into `parse-unary` and then let `^` bind to the already-negated operand. Added `parse-pow-chain` helper and changed the `else` branch of `parse-unary` to parse a primary + `^`-chain before returning; unary operators now wrap the full `^`-chain. Fixed `constructs.lua` past assert #3 (moved to compare-incompatible). 365/365 green (+3 precedence tests).
 - 2026-04-24: lua: scoreboard iteration — `lua-byte-to-char` regression fix. My previous change returned 2-char strings (`"\a"` etc.) for bytes that SX string literals can't express (0, 7, 8, 11, 12, 14–31, 127+), breaking `'a\0a'` length from 3 → 4. Now only 9/10/13 and printable 32-126 produce real bytes; others use a single `"?"` placeholder so `string.len` stays correct. literals.lua back to failing at assert #4 (was regressed to #2).