fix(webapp,clickhouse): pre-cap history keeps its truthful gap in the combined chart

The config-gauge back-fill exists to cover leading buckets with no
samples, but it also overwrote sampled history from before a combined
cap existed, showing a cap that was never in force. The cap series now
carries a sampled guard column and the back-fill skips sampled buckets.
Also corrects the renumbered migration's pre-044 comment.

Author: matt-aitken

apps/webapp/app/components/queues/QueueMetricCards.tsx

@@ -102,6 +102,12 @@ type QueueMetricChartProps = {
    * are config values that existed all along, so carry the first value backward instead.
    */
   carryBackfill?: string[];
+  /**
+   * Column that marks a bucket as genuinely sampled. When set, carryBackfill only
+   * overwrites buckets where this column is absent or zero, so history from before
+   * a config value existed keeps its truthful gap instead of inheriting the value.
+   */
+  carryBackfillGuard?: string;
   /** Show the series legend below the chart (use for multi-series charts). */
   showLegend?: boolean;
   /**
@@ -141,6 +147,7 @@ export function QueueMetricChart({
   defaultPeriod,
   warningOverlay,
   carryBackfill,
+  carryBackfillGuard,
   thresholdStroke,
   onHasDataChange,
   minBucketSeconds,
@@ -174,12 +181,15 @@ export function QueueMetricChart({
         const first = points.findIndex((p) => toNumber(p[key]) > 0);
         if (first > 0) {
           const value = points[first]![key]!;
-          for (let i = 0; i < first; i++) points[i]![key] = value;
+          for (let i = 0; i < first; i++) {
+            if (carryBackfillGuard && toNumber(points[i]![carryBackfillGuard]) > 0) continue;
+            points[i]![key] = value;
+          }
         }
       }
     }
     return points;
-  }, [rows, series, carryBackfill, sampleCountColumn]);
+  }, [rows, series, carryBackfill, carryBackfillGuard, sampleCountColumn]);
 
   const chartConfig = useMemo(() => {
     const cfg: ChartConfig = {};

apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.queues_.$queueParam/route.tsx

@@ -499,7 +499,7 @@ function OverviewCharts({
             }
             showLegend
             className="aspect-[2/1]"
-            query={`SELECT timeBucket() AS t, max(max_total_running) AS running, least(nullIf(max(max_total_limit), 0), max(max_env_limit)) AS cap\nFROM concurrency_metrics\nGROUP BY t\nORDER BY t`}
+            query={`SELECT timeBucket() AS t, max(max_total_running) AS running, least(nullIf(max(max_total_limit), 0), max(max_env_limit)) AS cap, max(max_env_limit) AS sampled\nFROM concurrency_metrics\nGROUP BY t\nORDER BY t`}
             fillGaps
             minBucketSeconds={SYNCED_CHART_MIN_BUCKET_SECONDS}
             ids={ids}
@@ -515,6 +515,7 @@ function OverviewCharts({
               aboveColor: "var(--color-warning)",
             }}
             carryBackfill={["cap"]}
+            carryBackfillGuard="sampled"
           />
         ) : null}
         <QueueDetailChartCard

internal-packages/clickhouse/schema/044_add_queue_metrics_total_concurrency.sql

@@ -109,7 +109,7 @@ ALTER TABLE trigger_dev.queue_metrics_5m_v1 DROP COLUMN IF EXISTS max_total_runn
 ALTER TABLE trigger_dev.queue_metrics_v1 DROP COLUMN IF EXISTS max_total_running, DROP COLUMN IF EXISTS max_total_limit;
 ALTER TABLE trigger_dev.queue_metrics_raw_v1 DROP COLUMN IF EXISTS total_running, DROP COLUMN IF EXISTS total_limit;
 
--- Recreate the pre-042 materialized views (the definitions from 036) so ingestion keeps
+-- Recreate the pre-044 materialized views (the definitions from 036) so ingestion keeps
 -- feeding every aggregate table after a rollback.
 CREATE MATERIALIZED VIEW IF NOT EXISTS trigger_dev.queue_metrics_mv_v1
 TO trigger_dev.queue_metrics_v1 AS