lua: math.mod (alias) + math.frexp + math.ldexp

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._
 
+- 2026-04-25: lua: scoreboard iteration — `math.mod` (Lua 5.0 alias for `fmod`), `math.frexp` (mantissa/exponent split), `math.ldexp` (m·2^e). math.lua moves past line-103 `math.mod` call. Timeouts 6→3, asserts 5→7. 393/393 green.
 - 2026-04-25: lua: scoreboard iteration — `unpack(t, i, j)` now treats explicit nil for `i` or `j` as missing (defaults to 1 and `#t`). vararg.lua-style `unpack(args, 1, args.n)` works when `args.n` is nil. Asserts 4→5, timeouts 8→6 (more tests reach assertions instead of timing out). 393/393 green.
 - 2026-04-25: lua: scoreboard iteration — extended `string.format`. New `%x`/`%X`/`%o` (hex/octal), `%c` (codepoint→char via `lua-char-one`), `%q` (basic quote), width N (`%5d`), zero-pad (`%05d`), left-align (`%-5d`), `%.Ns` precision. Helpers `lua-fmt-pad` and `lua-fmt-int-base`. 393/393 green (+6 format tests).
 - 2026-04-25: lua: scoreboard iteration — `lua-eval-ast` now SKIPS the top-level guard when the parsed chunk has no top-level `return` (recursive AST walk via `lua-has-top-return?` that descends through control-flow but stops at function-body boundaries). Without the guard, top-level user defines leak to the SX top env, and `loadstring`-captured closures can find them. Verified: `function fat(x)...loadstring("return fat(...)")...end; x=fat(5)` works (was undefined). Most PUC-Rio tests still have top-level returns elsewhere, so they still need the guard. Scoreboard unchanged at 1/16 but unblocks future work.