Method getRobustDate

src/utils/usage-tracker.ts:395–410

* Get robust date for a pattern (P90 percentile) to avoid "single file edit" skew * This means we take the date of the 10th percentile newest file. * For example, if there are 100 files, we take the 10th newest file's date. * This allows ~10% of legacy files to be edited without resetting t

(category: string, patternName: string)

   * This allows ~10% of legacy files to be edited without resetting the trend.
   */
  private getRobustDate(category: string, patternName: string): Date | undefined {
    const dates = this.patternFileDates.get(`${category}:${patternName}`);
    if (!dates || dates.length === 0) return undefined;

    // Sort descending (newest first)
    dates.sort((a, b) => b - a);

    // If few samples, trust the newest (not enough for stats)
    if (dates.length < 5) return new Date(dates[0]);

    // Use 90th percentile (exclude top 10% outliers)
    // For 100 files, P90 is index 10 (11th newest file)
    // This allows ~10% of legacy files to be edited without resetting the trend
    const p90Index = Math.floor(dates.length * 0.1);
    return new Date(dates[p90Index]);
  }

  getConsensus(category: string): PatternUsageStats[string] | null {
    const categoryPatterns = this.patterns.get(category);