fix: forward resample algorithm to metric store for running jobs

Only archived job data and internal-store node-list data honoured the
selected resample algorithm. For running jobs the algorithm was dropped:
MetricDataRepository.LoadData had no such parameter, so the memory store
fell back to an empty string, which cc-lib's GetResampler maps to LTTB.
The external store client was worse - its APIQueryRequest had no
ResampleAlgo field at all, and LoadNodeListData accepted the parameter
without using it.

Add resampleAlgo to the LoadData interface (mirroring LoadNodeListData),
forward it from metricdispatch, and set it on both stores' requests. The
field is tagged omitempty, so the wire format is unchanged when empty -
verify the deployed cc-metric-store accepts it before relying on it there.

The REST job endpoints pass a non-zero resolution and therefore do
resample, so they now request the configured default instead of an empty
string. Add config.ResampleAlgo() for that, since "" is not a neutral
value at this layer.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/metricstoreclient/cc-metric-store.go

@@ -81,13 +81,14 @@ type CCMetricStore struct {
 // APIQueryRequest represents a request to the cc-metric-store query API.
 // It supports both explicit queries and "for-all-nodes" bulk queries.
 type APIQueryRequest struct {
-	Cluster     string     `json:"cluster"`       // Target cluster name
-	Queries     []APIQuery `json:"queries"`       // Explicit list of metric queries
-	ForAllNodes []string   `json:"for-all-nodes"` // Metrics to query for all nodes
-	From        int64      `json:"from"`          // Start time (Unix timestamp)
-	To          int64      `json:"to"`            // End time (Unix timestamp)
-	WithStats   bool       `json:"with-stats"`    // Include min/avg/max statistics
-	WithData    bool       `json:"with-data"`     // Include time series data points
+	Cluster      string     `json:"cluster"`                 // Target cluster name
+	Queries      []APIQuery `json:"queries"`                 // Explicit list of metric queries
+	ForAllNodes  []string   `json:"for-all-nodes"`           // Metrics to query for all nodes
+	From         int64      `json:"from"`                    // Start time (Unix timestamp)
+	To           int64      `json:"to"`                      // End time (Unix timestamp)
+	WithStats    bool       `json:"with-stats"`              // Include min/avg/max statistics
+	WithData     bool       `json:"with-data"`               // Include time series data points
+	ResampleAlgo string     `json:"resample-algo,omitempty"` // Downsampling algorithm ("lttb", "average", "simple"); empty = server default
 }
 
 // APIQuery specifies a single metric query with optional scope filtering.
@@ -231,6 +232,7 @@ func (ccms *CCMetricStore) LoadData(
 	scopes []schema.MetricScope,
 	ctx context.Context,
 	resolution int,
+	resampleAlgo string,
 ) (schema.JobData, error) {
 	queries, assignedScope, err := ccms.buildQueries(job, metrics, scopes, resolution)
 	if err != nil {
@@ -245,12 +247,13 @@ func (ccms *CCMetricStore) LoadData(
 	}
 
 	req := APIQueryRequest{
-		Cluster:   job.Cluster,
-		From:      job.StartTime,
-		To:        job.StartTime + int64(job.Duration),
-		Queries:   queries,
-		WithStats: true,
-		WithData:  true,
+		Cluster:      job.Cluster,
+		From:         job.StartTime,
+		To:           job.StartTime + int64(job.Duration),
+		Queries:      queries,
+		WithStats:    true,
+		WithData:     true,
+		ResampleAlgo: resampleAlgo,
 	}
 
 	resBody, err := ccms.doRequest(ctx, &req)
@@ -632,12 +635,13 @@ func (ccms *CCMetricStore) LoadNodeListData(
 	}
 
 	req := APIQueryRequest{
-		Cluster:   cluster,
-		Queries:   queries,
-		From:      from.Unix(),
-		To:        to.Unix(),
-		WithStats: true,
-		WithData:  true,
+		Cluster:      cluster,
+		Queries:      queries,
+		From:         from.Unix(),
+		To:           to.Unix(),
+		WithStats:    true,
+		WithData:     true,
+		ResampleAlgo: resampleAlgo,
 	}
 
 	resBody, err := ccms.doRequest(ctx, &req)