metrics: sift_batch_* series (jobs, targets, depth, in-flight, durations, bytes)

New internal/metrics/batch.go adds the batch series to metrics.Set, registered
in New: BatchJobsTotal and BatchTargetsTotal counters (label "outcome", any
value outside the known set folded to "other" so a raw string never becomes a
label), BatchQueueDepth and BatchTargetsInflight gauges, BatchJobSeconds and
BatchTargetSeconds histograms (the existing request buckets) and
BatchResultBytes (1K,4K,16K,64K,256K,1M). The Observe…/Set… methods are
nil-receiver safe like ObservePDF and flow through the existing /metrics
handler; no new endpoint or Snapshot change.

Co-Authored-By: ornith-1.5-35b-a3b <ornith-1.5-35b-a3b@llama.cpp.invalid>

internal/metrics/batch.go

@@ -0,0 +1,80 @@
+package metrics
+
+import "time"
+
+var batchResultBytesBuckets = []float64{1024, 4096, 16384, 65536, 262144, 1048576}
+
+var batchJobOutcomes = map[string]struct{}{
+	"created": {}, "reused": {}, "done": {}, "partial": {},
+	"failed": {}, "cancelled": {}, "restart": {},
+}
+
+var batchTargetOutcomes = map[string]struct{}{
+	"ok": {}, "blocked": {}, "timeout": {}, "busy": {},
+	"upstream_4xx": {}, "upstream_5xx": {}, "unsupported": {},
+	"too_long": {}, "cancel": {},
+}
+
+// ObserveBatchJob records one batch outcome. Values outside the known set fold
+// to "other" so a raw string never becomes a label.
+func (s *Set) ObserveBatchJob(outcome string) {
+	if s == nil {
+		return
+	}
+	if _, ok := batchJobOutcomes[outcome]; !ok {
+		outcome = "other"
+	}
+	s.BatchJobsTotal.WithLabelValues(outcome).Inc()
+}
+
+// ObserveBatchTarget records one target outcome. Values outside the known set
+// fold to "other" so a raw string never becomes a label.
+func (s *Set) ObserveBatchTarget(outcome string) {
+	if s == nil {
+		return
+	}
+	if _, ok := batchTargetOutcomes[outcome]; !ok {
+		outcome = "other"
+	}
+	s.BatchTargetsTotal.WithLabelValues(outcome).Inc()
+}
+
+// SetBatchQueueDepth sets the live job count gauge (queued+running).
+func (s *Set) SetBatchQueueDepth(n int) {
+	if s == nil {
+		return
+	}
+	s.BatchQueueDepth.Set(float64(n))
+}
+
+// SetBatchTargetsInflight sets the in-flight targets gauge.
+func (s *Set) SetBatchTargetsInflight(n int) {
+	if s == nil {
+		return
+	}
+	s.BatchTargetsInflight.Set(float64(n))
+}
+
+// ObserveBatchJobSeconds records the wall time from submit to a batch's terminal status.
+func (s *Set) ObserveBatchJobSeconds(d time.Duration) {
+	if s == nil {
+		return
+	}
+	s.BatchJobSeconds.Observe(d.Seconds())
+}
+
+// ObserveBatchTargetSeconds records the wall time for one target fetch.
+func (s *Set) ObserveBatchTargetSeconds(d time.Duration) {
+	if s == nil {
+		return
+	}
+	s.BatchTargetSeconds.Observe(d.Seconds())
+}
+
+// ObserveBatchResultBytes records the stored byte count of one target result.
+func (s *Set) ObserveBatchResultBytes(n int) {
+	if s == nil {
+		return
+	}
+	s.BatchResultBytes.Observe(float64(n))
+}