fix: normalize usage timeline buckets

apps/ui/js/usage.js

@@ -76,6 +76,96 @@ document.addEventListener('DOMContentLoaded', function () {
     return 'Wk ' + (index + 1);
   }
 
+  function toUtcBucketStart(date, period) {
+    var bucket = new Date(date.getTime());
+    bucket.setUTCMilliseconds(0);
+    bucket.setUTCSeconds(0);
+    bucket.setUTCMinutes(0);
+    bucket.setUTCHours(0);
+
+    if (period === '30d' || period === 'this_month') {
+      var day = bucket.getUTCDay();
+      var offset = day === 0 ? 6 : (day - 1);
+      bucket.setUTCDate(bucket.getUTCDate() - offset);
+      return bucket;
+    }
+
+    if (period === '90d') {
+      bucket.setUTCDate(1);
+      return bucket;
+    }
+
+    return bucket;
+  }
+
+  function shiftUtcBucket(date, period, amount) {
+    var shifted = new Date(date.getTime());
+    if (period === '30d' || period === 'this_month') {
+      shifted.setUTCDate(shifted.getUTCDate() + (amount * 7));
+      return shifted;
+    }
+    if (period === '90d') {
+      shifted.setUTCMonth(shifted.getUTCMonth() + amount);
+      return shifted;
+    }
+    shifted.setUTCDate(shifted.getUTCDate() + amount);
+    return shifted;
+  }
+
+  function bucketKey(date) {
+    return date.toISOString().slice(0, 19) + 'Z';
+  }
+
+  function expectedBucketCount(period, endBucket) {
+    if (period === '7d') {
+      return 7;
+    }
+    if (period === '30d') {
+      return 5;
+    }
+    if (period === '90d') {
+      return 4;
+    }
+    if (period === 'this_month') {
+      var firstDay = new Date(Date.UTC(endBucket.getUTCFullYear(), endBucket.getUTCMonth(), 1));
+      var firstWeek = toUtcBucketStart(firstDay, period);
+      var diffMs = endBucket.getTime() - firstWeek.getTime();
+      return Math.max(1, Math.floor(diffMs / (7 * 24 * 60 * 60 * 1000)) + 1);
+    }
+    return 7;
+  }
+
+  function normalizeTimeline(timeline, period) {
+    if (!timeline.length) {
+      return [];
+    }
+
+    var byBucket = {};
+    timeline.forEach(function(point) {
+      byBucket[point.bucket_start] = point;
+    });
+
+    var latestBucket = timeline.reduce(function(current, point) {
+      return point.bucket_start > current.bucket_start ? point : current;
+    }, timeline[0]);
+    var endBucket = toUtcBucketStart(new Date(latestBucket.bucket_start), period);
+    var bucketCount = expectedBucketCount(period, endBucket);
+    var startBucket = shiftUtcBucket(endBucket, period, -(bucketCount - 1));
+    var normalized = [];
+
+    for (var index = 0; index < bucketCount; index += 1) {
+      var bucketDate = shiftUtcBucket(startBucket, period, index);
+      var key = bucketKey(bucketDate);
+      normalized.push(byBucket[key] || {
+        bucket_start: key,
+        calls_ok: 0,
+        calls_error: 0,
+      });
+    }
+
+    return normalized;
+  }
+
   function renderEmpty(title, message) {
     chartWrap.innerHTML =
       '<div class="empty-state" style="width:100%;">' +
@@ -125,7 +215,7 @@ document.addEventListener('DOMContentLoaded', function () {
   }
 
   function renderChart() {
-    var timeline = state.usage ? state.usage.timeline : [];
+    var timeline = state.usage ? normalizeTimeline(state.usage.timeline || [], state.period) : [];
     chartWrap.innerHTML = '';
 
     if (!timeline.length) {