feat: default to average downsampling

Average consolidation makes every plotted point the true arithmetic mean of
its interval, which is what the Ganglia-style plot appearance depends on.
LTTB deliberately keeps extremes instead, so a plot downsampled with it
cannot be read as interval means.

resolveResampleAlgo used to return an empty string when neither the user nor
the config had chosen an algorithm, and cc-lib's GetResampler maps that to
LTTB. Route every fallback through config.ResampleAlgo() and ship "average"
as the generated and example default.

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

cmd/cc-backend/init.go

@@ -25,7 +25,7 @@ const configString = `
     "short-running-jobs-duration": 300,
     "resampling": {
       "default-policy": "medium",
-      "default-algo": "lttb"
+      "default-algo": "average"
     },
     "api-allowed-ips": [
       "*"

configs/config.json

@@ -15,7 +15,7 @@
     },
     "resampling": {
       "default-policy": "medium",
-      "default-algo": "lttb"
+      "default-algo": "average"
     },
     "footer-links": {
       "imprint": "/imprint",

internal/config/schema.go

@@ -98,7 +98,7 @@ var configSchema = `
           "enum": ["low", "medium", "high"]
         },
         "default-algo": {
-          "description": "Default resample algorithm when no user preference is set.",
+          "description": "Default resample algorithm when no user preference is set. Default and recommended: 'average' (RRDTool-style interval averaging).",
           "type": "string",
           "enum": ["lttb", "average", "simple"]
         }

internal/graph/resample.go

@@ -63,12 +63,12 @@ func resolveResampleAlgo(ctx context.Context, resampleAlgo *model.ResampleAlgo)
 
 	user := repository.GetUserFromContext(ctx)
 	if user == nil {
-		return ""
+		return config.ResampleAlgo()
 	}
 
 	conf, err := repository.GetUserCfgRepo().GetUIConfig(user)
 	if err != nil {
-		return ""
+		return config.ResampleAlgo()
 	}
 
 	algoVal, ok := conf["plotConfiguration_resampleAlgo"]
@@ -78,12 +78,8 @@ func resolveResampleAlgo(ctx context.Context, resampleAlgo *model.ResampleAlgo)
 		}
 	}
 
-	// Fall back to global default algo
-	if config.Keys.EnableResampling != nil && config.Keys.EnableResampling.DefaultAlgo != "" {
-		return config.Keys.EnableResampling.DefaultAlgo
-	}
-
-	return ""
+	// Fall back to the global default algo
+	return config.ResampleAlgo()
 }
 
 // resolveResolutionFromDefaultPolicy computes a resolution using the global

web/frontend/src/config/user/PlotRenderOptions.svelte

@@ -301,7 +301,10 @@
             </div>
           {/each}
           <div id="resampleAlgoHelp" class="form-text">
-            Algorithm used when downsampling time-series data. LTTB preserves visual shape, Average smooths data, Simple picks every Nth point.
+            Algorithm used when downsampling time-series data. Average (the
+            default) makes every plotted point the true mean of its interval,
+            LTTB preserves visual shape by keeping extremes, Simple picks every
+            Nth point.
           </div>
         </div>
         <Button color="primary" type="submit">Submit</Button>