feat: add delta mode for counter metrics using ClickHouse lag()

Counter metrics like chunks.exported.count are monotonically increasing.
Add mode=delta query parameter to the agent metrics API that computes
per-bucket deltas server-side using ClickHouse lag() window function:
max(value) per bucket, then greatest(0, current - previous) to get the
increase per period with counter-reset handling.

The chunks exported/dropped charts now show throughput per bucket
instead of the ever-increasing cumulative total.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/AgentMetricsController.java

@@ -27,15 +27,17 @@ public class AgentMetricsController {
             @RequestParam String names,
             @RequestParam(required = false) Instant from,
             @RequestParam(required = false) Instant to,
-            @RequestParam(defaultValue = "60") int buckets) {
+            @RequestParam(defaultValue = "60") int buckets,
+            @RequestParam(defaultValue = "gauge") String mode) {
 
         if (from == null) from = Instant.now().minus(1, ChronoUnit.HOURS);
         if (to == null) to = Instant.now();
 
         List<String> metricNames = Arrays.asList(names.split(","));
 
-        Map<String, List<MetricTimeSeries.Bucket>> raw =
+        Map<String, List<MetricTimeSeries.Bucket>> raw = "delta".equalsIgnoreCase(mode)
-                metricsQueryStore.queryTimeSeries(agentId, metricNames, from, to, buckets);
+                ? metricsQueryStore.queryTimeSeriesDelta(agentId, metricNames, from, to, buckets)
+                : metricsQueryStore.queryTimeSeries(agentId, metricNames, from, to, buckets);
 
         Map<String, List<MetricBucket>> result = raw.entrySet().stream()
                 .collect(Collectors.toMap(

cameleer3-server-app/src/main/java/com/cameleer3/server/app/storage/ClickHouseMetricsQueryStore.java

@@ -69,4 +69,57 @@ public class ClickHouseMetricsQueryStore implements MetricsQueryStore {
 
         return result;
     }
+
+    @Override
+    public Map<String, List<MetricTimeSeries.Bucket>> queryTimeSeriesDelta(
+            String instanceId, List<String> metricNames,
+            Instant from, Instant to, int buckets) {
+
+        long intervalSeconds = Math.max(60,
+                (to.getEpochSecond() - from.getEpochSecond()) / Math.max(buckets, 1));
+
+        Map<String, List<MetricTimeSeries.Bucket>> result = new LinkedHashMap<>();
+        for (String name : metricNames) {
+            result.put(name.trim(), new ArrayList<>());
+        }
+
+        String[] namesArray = metricNames.stream().map(String::trim).toArray(String[]::new);
+        String placeholders = String.join(", ", Collections.nCopies(namesArray.length, "?"));
+
+        String finalSql = """
+            SELECT bucket, metric_name,
+                   greatest(0, max_val - lag(max_val, 1, max_val)
+                       OVER (PARTITION BY metric_name ORDER BY bucket)) AS avg_value
+            FROM (
+                SELECT toStartOfInterval(collected_at, INTERVAL %d SECOND) AS bucket,
+                       metric_name,
+                       max(metric_value) AS max_val
+                FROM agent_metrics
+                WHERE tenant_id = ?
+                  AND instance_id = ?
+                  AND collected_at >= ?
+                  AND collected_at < ?
+                  AND metric_name IN (%s)
+                GROUP BY bucket, metric_name
+            )
+            ORDER BY bucket
+            """.formatted(intervalSeconds, placeholders);
+
+        List<Object> params = new ArrayList<>();
+        params.add(tenantId);
+        params.add(instanceId);
+        params.add(java.sql.Timestamp.from(from));
+        params.add(java.sql.Timestamp.from(to));
+        Collections.addAll(params, namesArray);
+
+        jdbc.query(finalSql, rs -> {
+            String metricName = rs.getString("metric_name");
+            Instant bucket = rs.getTimestamp("bucket").toInstant();
+            double value = rs.getDouble("avg_value");
+            result.computeIfAbsent(metricName, k -> new ArrayList<>())
+                    .add(new MetricTimeSeries.Bucket(bucket, value));
+        }, params.toArray());
+
+        return result;
+    }
 }

cameleer3-server-core/src/main/java/com/cameleer3/server/core/storage/MetricsQueryStore.java

@@ -11,4 +11,11 @@ public interface MetricsQueryStore {
     Map<String, List<MetricTimeSeries.Bucket>> queryTimeSeries(
             String instanceId, List<String> metricNames,
             Instant from, Instant to, int buckets);
+
+    /** Counter mode: returns per-bucket deltas (max - previous max, floored at 0). */
+    default Map<String, List<MetricTimeSeries.Bucket>> queryTimeSeriesDelta(
+            String instanceId, List<String> metricNames,
+            Instant from, Instant to, int buckets) {
+        return queryTimeSeries(instanceId, metricNames, from, to, buckets);
+    }
 }

ui/src/api/queries/agent-metrics.ts

@@ -9,15 +9,17 @@ export function useAgentMetrics(
   buckets = 60,
   from?: string,
   to?: string,
+  mode: 'gauge' | 'delta' = 'gauge',
 ) {
   const refetchInterval = useRefreshInterval(30_000);
   return useQuery({
-    queryKey: ['agent-metrics', agentId, names.join(','), buckets, from, to],
+    queryKey: ['agent-metrics', agentId, names.join(','), buckets, from, to, mode],
     queryFn: async () => {
       const token = useAuthStore.getState().accessToken;
       const params = new URLSearchParams({
         names: names.join(','),
         buckets: String(buckets),
+        mode,
       });
       if (from) params.set('from', from);
       if (to) params.set('to', to);

ui/src/pages/AgentInstance/AgentInstance.tsx

@@ -75,7 +75,7 @@ export default function AgentInstance() {
   const { data: agentMetrics } = useAgentMetrics(
     agent?.instanceId || null,
     ['cameleer.chunks.exported.count', 'cameleer.chunks.dropped.count'],
-    60, timeFrom, timeTo,
+    60, timeFrom, timeTo, 'delta',
   );
 
   const feedEvents = useMemo<FeedEvent[]>(() => {