fix: bestLane timeCount bug, denPlace null narrowing

- bestLane averaged time over all runs including untimed; now uses
  separate timeCount for timed-only average
- Add denPlace guard before showDen for TypeScript strict null narrowing
- Add test for mixed timed/untimed runs on the same lane

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

Author: Rio517

src/frontend/lib/racer-stats.ts

@@ -10,13 +10,14 @@ export function bestLane(history: RacerHistoryEntry[]): number | null {
   const valid = history.filter(h => !h.dnf && h.place != null);
   if (valid.length === 0) return null;
 
-  const byLane = new Map<number, { totalTime: number; totalPlace: number; count: number; hasTimes: boolean }>();
+  const byLane = new Map<number, { totalTime: number; timeCount: number; totalPlace: number; count: number; hasTimes: boolean }>();
   for (const h of valid) {
-    const entry = byLane.get(h.lane_number) ?? { totalTime: 0, totalPlace: 0, count: 0, hasTimes: false };
+    const entry = byLane.get(h.lane_number) ?? { totalTime: 0, timeCount: 0, totalPlace: 0, count: 0, hasTimes: false };
     entry.totalPlace += h.place!;
     entry.count++;
     if (h.time_ms != null && h.time_ms > 0) {
       entry.totalTime += h.time_ms;
+      entry.timeCount++;
       entry.hasTimes = true;
     }
     byLane.set(h.lane_number, entry);
@@ -30,7 +31,7 @@ export function bestLane(history: RacerHistoryEntry[]): number | null {
   let bestScore = Infinity;
   for (const [lane, stats] of byLane) {
     if (anyTimed && !stats.hasTimes) continue;
-    const score = anyTimed ? stats.totalTime / stats.count : stats.totalPlace / stats.count;
+    const score = anyTimed ? stats.totalTime / stats.timeCount : stats.totalPlace / stats.count;
     if (score < bestScore) {
       bestScore = score;
       best = lane;

src/frontend/views/RacerProfileView.tsx

@@ -266,7 +266,7 @@ export function RacerProfileView() {
               totalRacers={racers.length}
             />
 
-            {showDen && (
+            {denPlace && showDen && (
               <DenPlacementStrip rank={denPlace.rank} den={denPlace.den} isPodium={rank !== null && rank <= 3} />
             )}
 

tests/best-lane.test.ts

@@ -78,4 +78,15 @@ describe('bestLane', () => {
     // Lane 1 is the only timed lane, so it wins
     expect(bestLane(history)).toBe(1);
   });
+
+  it('averages time only over timed runs on the same lane', () => {
+    const history = [
+      entry(1, 1, 3000),
+      entry(1, 2),        // untimed run — should not dilute avg time
+      entry(2, 1, 3100),
+    ];
+    // Lane 1 avg time: 3000/1 = 3000 (not 3000/2 = 1500)
+    // Lane 2 avg time: 3100/1 = 3100
+    expect(bestLane(history)).toBe(1);
+  });
 });