lua: break via guard+raise sentinel; auto-first multi in arith/concat +4 tests

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).