promql: add temporary debug logging to yrate start-timestamp codepath

Logs when start timestamps are found during yrate/yincrease evaluation
and when they trigger counter reset detection. This is temporary logging
for integration testing on red.prodref — to be removed after validation.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Shannon Price <sprice@invoca.com>

Author: dasbus

promql/yrate_funcs.go

@@ -14,10 +14,15 @@
 package promql
 
 import (
+"log/slog"
+
 "github.com/prometheus/prometheus/promql/parser"
 "github.com/prometheus/prometheus/util/annotations"
 )
 
+// TEMPORARY: debug logger for start-timestamp verification. Remove after integration testing.
+varyrateSTLogger=slog.Default().With("component", "yrate-st-debug")
+
 // yIncrease is a utility function for yincrease/yrate/ydelta.
 // It calculates the increase of the range (allowing for counter resets if isCounter is true),
 // taking into account the sample at the end of the previous range (just before rangeStartMsec).
@@ -66,6 +71,17 @@ func yIncrease(points []FPoint, rangeStartMsec, rangeEndMsec int64, isCounter bo
 ifisCounter&&isYCounterReset(startTimestamps, prevST, currentST, points[i].T, rangeStartMsec, points[i].F, lastInRange) {
 // Counter reset: accumulate as if 0 had come before this sample.
 inRangeResetIncreases+=lastInRange
+// TEMPORARY: log counter reset detection details.
+stTriggered:=startTimestamps!=nil&&currentST!=0&&currentST!=prevST
+yrateSTLogger.Info("yrate counter reset detected",
+"value_drop", points[i].F<lastInRange,
+"st_triggered", stTriggered,
+"prev_st", prevST,
+"current_st", currentST,
+"sample_t", points[i].T,
+"sample_value", points[i].F,
+"last_in_range", lastInRange,
+ )
 
 if!foundInRangeSample {
 // This reset was *also* the first in-range sample. Since we just counted
@@ -132,8 +148,14 @@ func funcYrate(_ []Vector, matrixVals Matrix, args parser.Expressions, enh *Eval
 funcyStartTimestamps(points []FPoint, enh*EvalNodeHelper) []int64 {
 ifenh.StartTimestamps!=nil&&len(enh.StartTimestamps.Floats) ==len(points) {
 startTimestamps:=enh.StartTimestamps.Floats
-for_, startTimestamp:=rangestartTimestamps {
+fori, startTimestamp:=rangestartTimestamps {
 ifstartTimestamp!=0 {
+// TEMPORARY: log when start timestamps are found for yrate/yincrease evaluation.
+yrateSTLogger.Info("start timestamps found for yrate evaluation",
+"num_points", len(points),
+"first_nonzero_st_index", i,
+"first_nonzero_st_value", startTimestamp,
+ )
 returnstartTimestamps
  }
  }