feat: add bounded prediction cache (max 100 entries, FIFO eviction)

- Before inserting into predictionCacheRef, check if size >= 100
- If so, evict oldest entry via cache.keys().next().value (FIFO)
- Applied at both cache write sites (lines ~549 and ~671 in page.tsx)
- Marks task 8.5 as done in tasks.md

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

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

@@ -74,7 +74,7 @@
 - [x] 8.2 `[sonnet]` Use `chart.applyOptions()` for theme changes instead of re-creating chart (`src/components/CandleChart.tsx:333`)
 - [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`)
-- [ ] 8.5 `[sonnet]` Add bounded prediction cache (max 100 entries, FIFO eviction) to `predictionCacheRef` (`src/app/page.tsx:195-199`)
+- [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`)
 - [ ] 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/app/page.tsx

@@ -544,9 +544,13 @@ export default function Home() {
 
       const data = await response.json();
 
-      // Cache the results
+      // Cache the results (bounded: max 100 entries, FIFO eviction)
       if (cacheKey) {
-        predictionCacheRef.current.set(cacheKey, {
+        const cache = predictionCacheRef.current;
+        if (cache.size >= 100) {
+          cache.delete(cache.keys().next().value);
+        }
+        cache.set(cacheKey, {
           spans: data.spans,
           predictions: data.predictions,
           modelVersion: data.model_info.model_version,
@@ -668,7 +672,11 @@ export default function Home() {
 
       const cacheKey = generateCacheKey(activeChartId, data.model_info.model_version);
       if (cacheKey) {
-        predictionCacheRef.current.set(cacheKey, {
+        const cache = predictionCacheRef.current;
+        if (cache.size >= 100) {
+          cache.delete(cache.keys().next().value);
+        }
+        cache.set(cacheKey, {
           spans: data.spans,
           predictions: data.predictions,
           modelVersion: data.model_info.model_version,