chore: import upstream snapshot with attribution

pkg/observability/metrics/metrics.go

@@ -0,0 +1,13 @@
+package metrics
+
+import "time"
+
+// Metrics is a backend-agnostic interface for emitting metrics.
+// Implementations can route to DataDog, log to slog, or discard (noop).
+type Metrics interface {
+	Increment(key string, tags map[string]string)
+	Counter(key string, tags map[string]string, value int64)
+	Distribution(key string, tags map[string]string, value float64)
+	DistributionMs(key string, tags map[string]string, value time.Duration)
+	WithTags(tags map[string]string) Metrics
+}

pkg/observability/metrics/noop_sink.go

@@ -0,0 +1,19 @@
+package metrics
+
+import "time"
+
+// NoopMetrics is a no-op implementation of the Metrics interface.
+type NoopMetrics struct{}
+
+var _ Metrics = (*NoopMetrics)(nil)
+
+// NewNoopMetrics returns a new NoopMetrics.
+func NewNoopMetrics() *NoopMetrics {
+	return &NoopMetrics{}
+}
+
+func (n *NoopMetrics) Increment(_ string, _ map[string]string)                       {}
+func (n *NoopMetrics) Counter(_ string, _ map[string]string, _ int64)                {}
+func (n *NoopMetrics) Distribution(_ string, _ map[string]string, _ float64)         {}
+func (n *NoopMetrics) DistributionMs(_ string, _ map[string]string, _ time.Duration) {}
+func (n *NoopMetrics) WithTags(_ map[string]string) Metrics                          { return n }

pkg/observability/metrics/noop_sink_test.go

@@ -0,0 +1,42 @@
+package metrics
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNoopMetrics_ImplementsInterface(_ *testing.T) {
+	var _ Metrics = (*NoopMetrics)(nil)
+}
+
+func TestNoopMetrics_NoPanics(t *testing.T) {
+	m := NewNoopMetrics()
+
+	assert.NotPanics(t, func() {
+		m.Increment("key", map[string]string{"a": "b"})
+		m.Counter("key", map[string]string{"a": "b"}, 1)
+		m.Distribution("key", map[string]string{"a": "b"}, 1.5)
+		m.DistributionMs("key", map[string]string{"a": "b"}, time.Second)
+	})
+}
+
+func TestNoopMetrics_NilTags(t *testing.T) {
+	m := NewNoopMetrics()
+
+	assert.NotPanics(t, func() {
+		m.Increment("key", nil)
+		m.Counter("key", nil, 1)
+		m.Distribution("key", nil, 1.5)
+		m.DistributionMs("key", nil, time.Second)
+	})
+}
+
+func TestNoopMetrics_WithTags(t *testing.T) {
+	m := NewNoopMetrics()
+	tagged := m.WithTags(map[string]string{"env": "prod"})
+
+	assert.NotNil(t, tagged)
+	assert.Equal(t, m, tagged)
+}