fix: unify resample policy target-points table

The policy -> target-points mapping existed twice with different values:
internal/config (300/600/1000) fed the resampler's MinimumRequiredPoints
threshold, while internal/metricdispatch (200/500/1000) fed the requested
resolution and the frontend target point count.

Because the threshold was larger than the target, the resampler refused to
downsample series whose length fell between the two numbers, silently
dropping the resolution the backend had asked for. With the medium policy
that covered every series between 500 and 600 points.

Move the table into internal/config as the single source of truth (import
direction rules out the reverse, since metricdispatch already imports
config) and keep the 200/500/1000 values, which already drove the requested
resolution. metricdispatch.TargetPointsForPolicy now delegates to it, so
MinimumRequiredPoints equals the target and resampling happens exactly when
a series exceeds it.

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

internal/config/config.go

@@ -171,24 +171,41 @@ func Init(mainConfig json.RawMessage) {
 		cclog.Abortf("Config Init: Could not decode config file '%s'.\nError: %s\n", mainConfig, err.Error())
 	}
 
-	if Keys.EnableResampling != nil {
+	initResampler()
-		policy := Keys.EnableResampling.DefaultPolicy
-		if policy == "" {
-			policy = "medium"
-		}
-		resampler.SetMinimumRequiredPoints(targetPointsForPolicy(policy))
-	}
 }
 
-func targetPointsForPolicy(policy string) int {
+// initResampler aligns the resampler's MinimumRequiredPoints threshold with the
+// configured policy's target point count. The resampler must be allowed to act
+// exactly when a series is longer than that target; a different threshold here
+// silently drops resample requests for a band of job durations.
+func initResampler() {
+	if Keys.EnableResampling == nil {
+		return
+	}
+
+	policy := Keys.EnableResampling.DefaultPolicy
+	if policy == "" {
+		policy = DefaultResamplePolicy
+	}
+	resampler.SetMinimumRequiredPoints(TargetPointsForPolicy(policy))
+}
+
+// DefaultResamplePolicy is used when no resample policy is configured.
+const DefaultResamplePolicy = "medium"
+
+// TargetPointsForPolicy returns the target number of data points for a resample
+// policy. This is the single source of truth: it feeds both the requested
+// resolution (via metricdispatch.ComputeResolution) and the resampler's
+// MinimumRequiredPoints threshold. Unknown or empty policies return 0.
+func TargetPointsForPolicy(policy string) int {
 	switch policy {
 	case "low":
-		return 300
+		return 200
 	case "medium":
-		return 600
+		return 500
 	case "high":
 		return 1000
 	default:
-		return 600
+		return 0
 	}
 }

internal/config/config_test.go

@@ -10,6 +10,7 @@ import (
 
 	ccconf "github.com/ClusterCockpit/cc-lib/v2/ccConfig"
 	cclog "github.com/ClusterCockpit/cc-lib/v2/ccLogger"
+	"github.com/ClusterCockpit/cc-lib/v2/resampler"
 )
 
 func TestInit(t *testing.T) {
@@ -39,3 +40,46 @@ func TestInitMinimal(t *testing.T) {
 		t.Errorf("wrong addr\ngot: %s \nwant: 127.0.0.1:8080", Keys.Addr)
 	}
 }
+
+func TestTargetPointsForPolicy(t *testing.T) {
+	tests := []struct {
+		policy string
+		want   int
+	}{
+		{"low", 200},
+		{"medium", 500},
+		{"high", 1000},
+		{"unknown", 0},
+		{"", 0},
+	}
+
+	for _, tt := range tests {
+		if got := TargetPointsForPolicy(tt.policy); got != tt.want {
+			t.Errorf("TargetPointsForPolicy(%q) = %d, want %d", tt.policy, got, tt.want)
+		}
+	}
+}
+
+// The resampler must be allowed to act exactly when a series exceeds the target
+// point count. A mismatch here silently drops resample requests for a band of
+// job durations.
+func TestInitSyncsResamplerThreshold(t *testing.T) {
+	for _, policy := range []string{"low", "medium", "high"} {
+		Keys.EnableResampling = &ResampleConfig{DefaultPolicy: policy}
+		initResampler()
+
+		want := TargetPointsForPolicy(policy)
+		if resampler.MinimumRequiredPoints != want {
+			t.Errorf("policy %q: MinimumRequiredPoints = %d, want %d",
+				policy, resampler.MinimumRequiredPoints, want)
+		}
+	}
+
+	// Empty policy falls back to the documented default.
+	Keys.EnableResampling = &ResampleConfig{}
+	initResampler()
+	if want := TargetPointsForPolicy(DefaultResamplePolicy); resampler.MinimumRequiredPoints != want {
+		t.Errorf("empty policy: MinimumRequiredPoints = %d, want %d",
+			resampler.MinimumRequiredPoints, want)
+	}
+}

internal/metricdispatch/resamplepolicy.go

@@ -4,7 +4,11 @@
 // license that can be found in the LICENSE file.
 package metricdispatch
 
-import "math"
+import (
+	"math"
+
+	"github.com/ClusterCockpit/cc-backend/internal/config"
+)
 
 type ResamplePolicy string
 
@@ -14,18 +18,12 @@ const (
 	ResamplePolicyHigh   ResamplePolicy = "high"
 )
 
-// TargetPointsForPolicy returns the target number of data points for a given policy.
+// TargetPointsForPolicy returns the target number of data points for a given
+// policy. The table lives in the config package so that the requested
+// resolution and the resampler's MinimumRequiredPoints threshold can never
+// diverge.
 func TargetPointsForPolicy(policy ResamplePolicy) int {
-	switch policy {
+	return config.TargetPointsForPolicy(string(policy))
-	case ResamplePolicyLow:
-		return 200
-	case ResamplePolicyMedium:
-		return 500
-	case ResamplePolicyHigh:
-		return 1000
-	default:
-		return 0
-	}
 }
 
 // ComputeResolution computes the resampling resolution in seconds for a given