refactor: remove ensureSampled, use natural OTel root spans

middleware/tracing.go

@@ -2,28 +2,21 @@ package middleware
 
 import (
 	"context"
-	"crypto/rand"
 
 	"github.com/go-coldbrew/log"
 	"github.com/go-coldbrew/tracing"
 	"github.com/go-coldbrew/workers"
 	oteltrace "go.opentelemetry.io/otel/trace"
 )
 
-// Tracing creates an OTEL span per cycle via go-coldbrew/tracing.
+// Tracing creates an OTEL root span per cycle via go-coldbrew/tracing.
 // The span is named "worker:<name>:cycle" and records errors.
-//
-// Worker spans are always sampled regardless of the global
-// TracerProvider's sampler. This prevents silent span drops when
-// using ParentBased(TraceIDRatioBased(ratio)), where worker root
-// spans (which have no parent) would otherwise be probabilistically
-// dropped.
+// Sampling is determined by the global TracerProvider's sampler.
 //
 // The OTEL trace ID is injected into the log context as "trace"
 // for correlation with the tracing backend.
 func Tracing() workers.Middleware {
 	return func(ctx context.Context, info *workers.WorkerInfo, next workers.CycleFunc) error {
-		ctx = ensureSampled(ctx)
 		span, ctx := tracing.NewInternalSpan(ctx, "worker:"+info.GetName()+":cycle")
 		defer span.Finish()
 
@@ -38,23 +31,3 @@ func Tracing() workers.Middleware {
 		return err
 	}
 }
-
-// ensureSampled injects a sampled remote span context so that
-// ParentBased samplers always sample the next span created from
-// this context. If the context already has a sampled span, it is
-// returned unchanged.
-func ensureSampled(ctx context.Context) context.Context {
-	if oteltrace.SpanFromContext(ctx).SpanContext().IsSampled() {
-		return ctx
-	}
-	var traceID oteltrace.TraceID
-	var spanID oteltrace.SpanID
-	_, _ = rand.Read(traceID[:])
-	_, _ = rand.Read(spanID[:])
-	return oteltrace.ContextWithRemoteSpanContext(ctx, oteltrace.NewSpanContext(oteltrace.SpanContextConfig{
-		TraceID:    traceID,
-		SpanID:     spanID,
-		TraceFlags: oteltrace.FlagsSampled,
-		Remote:     true,
-	}))
-}

middleware/tracing_test.go

@@ -6,7 +6,6 @@ import (
 
 	"github.com/go-coldbrew/workers"
 	"github.com/stretchr/testify/assert"
-	oteltrace "go.opentelemetry.io/otel/trace"
 )
 
 func TestTracing_NoPanic(t *testing.T) {
@@ -33,42 +32,3 @@ func TestTracing_PropagatesError(t *testing.T) {
 
 	assert.ErrorIs(t, err, assert.AnError)
 }
-
-func TestEnsureSampled(t *testing.T) {
-	// From a bare context (no span), ensureSampled should inject a
-	// sampled remote span context.
-	ctx := ensureSampled(context.Background())
-	sc := oteltrace.SpanContextFromContext(ctx)
-
-	assert.True(t, sc.IsSampled(), "should be sampled")
-	assert.True(t, sc.IsRemote(), "should be remote")
-	assert.True(t, sc.HasTraceID(), "should have a trace ID")
-	assert.True(t, sc.HasSpanID(), "should have a span ID")
-}
-
-func TestEnsureSampled_AlreadySampled(t *testing.T) {
-	// If context already has a sampled span, ensureSampled is a no-op.
-	existing := oteltrace.NewSpanContext(oteltrace.SpanContextConfig{
-		TraceID:    oteltrace.TraceID{1, 2, 3},
-		SpanID:     oteltrace.SpanID{4, 5, 6},
-		TraceFlags: oteltrace.FlagsSampled,
-		Remote:     true,
-	})
-	ctx := oteltrace.ContextWithRemoteSpanContext(context.Background(), existing)
-
-	ctx = ensureSampled(ctx)
-	sc := oteltrace.SpanContextFromContext(ctx)
-
-	assert.Equal(t, existing.TraceID(), sc.TraceID(), "should keep existing trace ID")
-	assert.Equal(t, existing.SpanID(), sc.SpanID(), "should keep existing span ID")
-}
-
-func TestEnsureSampled_UniqueIDs(t *testing.T) {
-	ctx1 := ensureSampled(context.Background())
-	ctx2 := ensureSampled(context.Background())
-
-	sc1 := oteltrace.SpanContextFromContext(ctx1)
-	sc2 := oteltrace.SpanContextFromContext(ctx2)
-
-	assert.NotEqual(t, sc1.TraceID(), sc2.TraceID(), "each call should generate unique trace IDs")
-}