[joeblau]

Closes #93
Closes #94

Behavior

Checks sit on the calls that write layout and scroll state. The render loop is unchanged.

• Invariant: canvas size and pixelRatio are finite and > 0 #93, canvas size and pixelRatio. The constructor and resize throw chart-ts: invalid pixelRatio … unless the ratio is finite and > 0, the same shape of error takeScreenshot already uses. resize also throws chart-ts: invalid chart width/height … unless both CSS sizes are finite and >= 0, and it does not change the canvas when it throws. resolveConfig and updateConfig reject a non-finite or negative width, height, priceAxis.width, or timeAxis.height before the config is stored. 0 stays a legal size.
• Invariant: the time scale's scroll offset stays finite #94, scroll offset. scroll, scrollTo, and fitRange (scrollBy, scrollTo, zoomToRange) ignore a non-finite argument, matching zoom. clampScroll resets a non-finite offset to 0 before clamping, so a NaN cannot stick across the next gesture.

Tests

1909 tests passed. Coverage is 100% line, branch, and function. bun run typecheck:tsc and bun run check:invariants passed.

Benchmarks

node bench/suite/run.mjs --samples=7 --sizes=100000, Node 24, median ms/op. The two builds were timed back to back. These paths do not run during setData, appendData, or render.

Case	Before	After
100000 setData sorted	1.0025	1.0617
100000 setData shuffled	28.4973	29.8749
100000 DataStore single bar append	0.0005	0.0005
100000 chart appendData streaming	0.2223	0.1965
100000 stored 200 visible redraw	0.7345	0.8024
100000 stored 200 visible live	0.7693	0.7990
100000 stored 5000 visible redraw	10.5311	9.0193
100000 stored 5000 visible live	9.0146	9.4136

The differences are run-to-run noise. Minimums for the 5000-bar redraw were 5.94 ms before and 5.77 ms after.