fix: detect candle interval dynamically instead of hardcoded 60s

Replace the hardcoded 60-second assumption in CandleChart.tsx with
dynamic interval detection: compute interval as candles[1].time -
candles[0].time when at least 2 candles are available, fall back to
60 otherwise. Used for span-to-prediction-time mapping iteration.

Marks task 8.6 as done in tasks.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openspec/changes/code-review-fix/tasks.md

@@ -75,7 +75,7 @@
 - [x] 8.3 `[sonnet]` Remove `fitContent()` from reconciliation effect, only call on initial load (`src/components/SpanAnnotationManager.tsx:160`)
 - [x] 8.4 `[opus]` Implement incremental primitive updates in SpanAnnotationManager: update only selection state on selection change, full reconciliation only on annotation list changes (`src/components/SpanAnnotationManager.tsx:104-161`)
 - [x] 8.5 `[sonnet]` Add bounded prediction cache (max 100 entries, FIFO eviction) to `predictionCacheRef` (`src/app/page.tsx:195-199`)
-- [ ] 8.6 `[sonnet]` Fix hardcoded 1-minute candle interval: detect interval from data, use for span iteration (`src/components/CandleChart.tsx:452`)
+- [x] 8.6 `[sonnet]` Fix hardcoded 1-minute candle interval: detect interval from data, use for span iteration (`src/components/CandleChart.tsx:452`)
 - [ ] 8.7 `[haiku]` Extract magic numbers (8px, 60s, colors) to named constants in `CandleChart.tsx`
 - [ ] 8.8 `[haiku]` Move `new Set<string>()` default prop to module-level constant in `CandleChart.tsx:125`
 

src/components/CandleChart.tsx

@@ -472,11 +472,14 @@ const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
       // Build candle price lookup for histogram values
       const candleMap = new Map(candles.map((c) => [c.time, c]));
 
+      // Detect candle interval from data (fall back to 60s if fewer than 2 candles)
+      const candleInterval = candles.length >= 2 ? candles[1].time - candles[0].time : 60;
+
       // Build a map from prediction time to its span for disagreement lookup
       const predictionTimeToSpan = new Map<number, PredictionSpan>();
       predictionSpans.forEach((span) => {
         // Associate all times in the span with the span object
-        for (let t = span.start_time; t <= span.end_time; t += 60) { // Assuming 1-minute candles, adjust if needed
+        for (let t = span.start_time; t <= span.end_time; t += candleInterval) {
           predictionTimeToSpan.set(t, span);
         }
       });