flat: walk with depth, recursive when element is list and depth>0.
fill(value, start?, end?): in-place mutation, returns self.
indexOf: honor second arg as start position.
396/398 unit (+5), 148/148 slice unchanged.
String global with fromCharCode (variadic). parseInt truncates via
js-math-trunc; parseFloat delegates to js-to-number. Wired into
js-global.
381/383 unit (+5), 148/148 slice unchanged.
Math gains sqrt/pow/trunc/sign/cbrt/hypot plus LN2/LN10/LOG2E/
LOG10E/SQRT2/SQRT1_2 constants and full-precision PI/E.
Number global: isFinite/isNaN/isInteger/isSafeInteger plus
MAX_VALUE/MIN_VALUE/MAX_SAFE_INTEGER/MIN_SAFE_INTEGER/EPSILON/
POSITIVE_INFINITY/NEGATIVE_INFINITY/NaN.
Global isFinite, isNaN, Infinity, NaN. Wired into js-global.
329/331 unit (+21), 148/148 slice unchanged.
Initial commit of the lib/js/ tree and plans/ directory. A previous
session left template-string work in progress — 278/280 unit tests pass
(2 failing: tpl part-count off-by-one, escaped-backtick ident lookup).
test262-runner.py and scoreboard are placeholders (0/8 with 7 timeouts);
fixing the runner is the next queue item.