fix double-reversal in unified hover: normalize entry order first

groupedHoverData arrives in inconsistent order depending on showlegend
and hover collection path. Sorting entries by trace.index before passing
to getLegendData ensures the reversal in getLegendData is the single
source of truth for traceorder.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ryan-williams

specs/done/double-reversal-unified-hover.md

@@ -0,0 +1,24 @@
+# Inconsistent unified hover tooltip ordering
+
+## Problem
+
+Unified hover entries arrive in inconsistent order depending on whether the plot has `showlegend: true` or `false`:
+
+- **Plot with `showlegend: false`** (custom legend): hover entries arrive in `groupedHoverData` already reversed (top-of-stack first). `getLegendData.reverse()` then double-reverses → wrong order.
+- **Plot with `showlegend: true`**: hover entries arrive in original trace array order (bottom-of-stack first). `getLegendData.reverse()` correctly reverses → right order.
+- But for CrashPlot (`showlegend: true`): the order is scrambled (Fatal, Prop. Damage, Injury instead of Prop. Damage, Injury, Fatal).
+
+## Debug evidence (Plot1, showlegend: false)
+
+```
+BEFORE_REVERSE: Total,Passengers,Pedestrians,Drivers,Cyclists  ← already reversed
+AFTER_REVERSE:  Cyclists,Drivers,Pedestrians,Passengers,Total  ← double-reversed, WRONG
+```
+
+## Root cause
+
+The `groupedHoverData` order depends on the plot's full layout processing. When `showlegend: false`, the trace iteration order during hover data collection may differ from when `showlegend: true`. The hover code in `hover.ts` builds entries in whatever order `hoverData` arrives, which depends on `_hoverPoints` in `plot_api.ts`.
+
+## Fix needed
+
+Normalize the hover entry order BEFORE passing to `getLegendData`. The entries should always arrive in trace array order (bottom-of-stack first), and `getLegendData.reverse()` should be the sole reversal. Find where `groupedHoverData` gets pre-reversed and prevent that.

src/components/fx/hover.ts

@@ -1233,7 +1233,11 @@ function createHoverText(hoverData: any[], opts: any): any {
 
             mockLegend.entries.push([pt]);
         }
-        // Sort is handled by getLegendData inside legendDraw,
+        // Normalize to trace index order before getLegendData applies traceorder.
+        // groupedHoverData may arrive in inconsistent order depending on
+        // showlegend and hover collection order.
+        mockLegend.entries.sort((a: any, b: any) => a[0].trace.index - b[0].trace.index);
+        // Reversal (if traceorder includes 'reversed') is handled by getLegendData inside legendDraw.
         // which respects traceorder (including 'reversed').
         mockLegend.layer = container;