fix(charts): collision-aware end-of-line labels when lines converge

Replace per-dataset label drawing with a post-pass in afterDatasetsDraw
that collects all museum line endpoints, sorts by Y, then pushes overlapping
labels apart with a connector line back to the actual data point.

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

src/config/chartConfig.ts

@@ -138,6 +138,8 @@ export const createBaseOptions = (showDataLabels: boolean): any => {
 // Only activates for charts that have datasets marked with _isMuseumLine.
 const trendLinePlugin = {
   id: 'trendLineOverlay',
+
+  // ── hover dim ──────────────────────────────────────────────────
   beforeDatasetDraw(chart: any, args: any) {
     if (!chart.data.datasets.some((ds: any) => ds._isMuseumLine)) return;
     const active = chart.getActiveElements();
@@ -149,30 +151,77 @@ const trendLinePlugin = {
   },
   afterDatasetDraw(chart: any, args: any) {
     if (!chart.data.datasets.some((ds: any) => ds._isMuseumLine)) return;
-    const ds = chart.data.datasets[args.index] as any;
     const active = chart.getActiveElements();
-    const isDimmed = active.length > 0 && active[0].datasetIndex !== args.index;
-    if (isDimmed) chart.ctx.restore();
+    if (active.length > 0 && active[0].datasetIndex !== args.index) {
+      chart.ctx.restore();
+    }
+  },
+
+  // ── end-of-line labels with collision resolution ───────────────
+  afterDatasetsDraw(chart: any) {
+    const MIN_GAP = 13;
+
+    // Collect last-point info for every visible museum line
+    type Entry = { label: string; color: string; x: number; actualY: number; placedY: number };
+    const entries: Entry[] = [];
+    chart.data.datasets.forEach((ds: any, i: number) => {
       if (!ds._isMuseumLine) return;
-    const meta = chart.getDatasetMeta(args.index);
+      const meta = chart.getDatasetMeta(i);
       if (meta.hidden) return;
       const vals = ds.data as number[];
-    let lastIdx = vals.length - 1;
-    while (lastIdx > 0 && !vals[lastIdx]) lastIdx--;
-    if (!vals[lastIdx]) return;
-    const pt = meta.data[lastIdx] as any;
+      let idx = vals.length - 1;
+      while (idx > 0 && !vals[idx]) idx--;
+      if (!vals[idx]) return;
+      const pt = meta.data[idx] as any;
       if (!pt) return;
       const name: string = ds.label;
-    const label = name.length > 22 ? name.slice(0, 20) + '…' : name;
+      entries.push({
+        label: name.length > 22 ? name.slice(0, 20) + '…' : name,
+        color: ds.borderColor,
+        x: pt.x,
+        actualY: pt.y,
+        placedY: pt.y,
+      });
+    });
+
+    if (entries.length === 0) return;
+
+    // Sort top → bottom, then push labels apart
+    entries.sort((a, b) => a.actualY - b.actualY);
+    for (let i = 1; i < entries.length; i++) {
+      if (entries[i].placedY - entries[i - 1].placedY < MIN_GAP) {
+        entries[i].placedY = entries[i - 1].placedY + MIN_GAP;
+      }
+    }
+
+    // Draw labels + connectors
     const ctx = chart.ctx;
+    for (const e of entries) {
       ctx.save();
+      // Small dot at the actual line tip
+      ctx.beginPath();
+      ctx.arc(e.x, e.actualY, 2.5, 0, Math.PI * 2);
+      ctx.fillStyle = e.color;
+      ctx.fill();
+      // Connector if label was displaced
+      if (Math.abs(e.placedY - e.actualY) > 3) {
+        ctx.beginPath();
+        ctx.moveTo(e.x + 5, e.actualY);
+        ctx.lineTo(e.x + 7, e.placedY);
+        ctx.strokeStyle = e.color;
+        ctx.globalAlpha = 0.45;
+        ctx.lineWidth = 0.8;
+        ctx.stroke();
+      }
+      ctx.globalAlpha = 1;
       ctx.font = '600 9px system-ui,-apple-system,sans-serif';
-    ctx.fillStyle = ds.borderColor;
+      ctx.fillStyle = e.color;
       ctx.textAlign = 'left';
       ctx.textBaseline = 'middle';
-    ctx.fillText(label, pt.x + 6, pt.y);
+      ctx.fillText(e.label, e.x + 9, e.placedY);
       ctx.restore();
     }
+  },
 };
 
 ChartJS.register(trendLinePlugin);