Trackside: fix Max Cell T + realtime Cell Thermals grid

[cyberneel]

What

• Fix "Max Cell T" stuck at 0. It read cell_top_temp (CAN 0x132), which HVC does not emit, so it sat at 0. Now uses the per-cell cells_temps[] array — the same source the driver park dash (dashd) uses on-car — taking the max over positive temps (the array is zero-padded for not-yet-reported cells). Falls back to the enricher's max_cell_temp scalar, then the legacy fields; requires > 0 so genuine no-data reads -- instead of a misleading 0.
• New "Cell Thermals" panel on the Live tab: a Grafana-style heatmap grid of every populated cell, fixed 20–60 °C blue→red scale, with min/avg/max in the header. Tooltip shows cell index + exact °C.

Why it was 0 (and the dash wasn't)

Two different sources: trackside read the unemitted 0x132 scalar; the dash computes max from the emitted 0x100 cells_temps[] array (zero-filtered). This aligns trackside to the dash's source.

Scope — client-only

The derived feed grafana_data_orion_derived already carries cells_temps (the bridge emits the array; the enricher passes lists through) plus a computed max_cell_temp. The only gaps were client-side: trackside read the wrong key, and flattenNumeric drops arrays. So this PR touches only the viewer_tool — no enricher/bridge/firmware changes.

Changes: LiveSample (+cellTemps, both type defs), normalizeLivePayload extracts the array, maxCellTempFor rewrite, CellThermalsPanel + CSS.

Verify

tsc --noEmit clean; next build green. Data path traced end-to-end (SSE JSON → event.sample.cellTemps → stored raw → smoothLiveSample preserves via spread → panel).

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Project	Deployment	Actions	Updated (UTC)
lhre-2026	Ready	Preview, Comment	Jun 18, 2026 4:14am

[gemini-code-assist]

Code Review

This pull request introduces a real-time per-cell thermal grid (heatmap) to the trackside live viewer. It extracts per-cell temperatures (cellTemps) from the telemetry feed, defines the CellThermalsPanel component to display the thermal grid with min, max, and average statistics, and updates the maxCellTempFor calculation to prioritize this array. The review feedback highlights potential stack overflow risks (RangeError) when using the spread operator with Math.min and Math.max on unvalidated arrays, suggesting the use of Array.prototype.reduce as a safer alternative.

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[gemini-code-assist]

Using the spread operator ... with Math.min and Math.max on an array of unvalidated size can lead to a stack overflow (RangeError: Maximum call stack size exceeded) if the array is unexpectedly large (e.g., due to corrupted telemetry data). It is safer and more defensive to use reduce to find the minimum and maximum values.

Suggested change

	const vals = populated.map((c) => c.t);
	const min = Math.min(...vals);
	const max = Math.max(...vals);
	const vals = populated.map((c) => c.t);
	const min = vals.reduce((m, t) => t < m ? t : m, Infinity);
	const max = vals.reduce((m, t) => t > m ? t : m, -Infinity);

[gemini-code-assist]

Using the spread operator ... with Math.max on an array of unvalidated size can lead to a stack overflow (RangeError: Maximum call stack size exceeded) if the array is unexpectedly large. It is safer and more defensive to use reduce to find the maximum value.

Suggested change

	const fromArray = sample.cellTemps?.filter((t) => t > 0) ?? [];
	if (fromArray.length) return Math.max(...fromArray);
	const fromArray = sample.cellTemps?.filter((t) => t > 0) ?? [];
	if (fromArray.length) return fromArray.reduce((max, t) => t > max ? t : max, -Infinity);