fix(webhook): preserve trace context across async detach via WithoutCancel

pkg/modules/webhook/async_context.go

@@ -11,22 +11,30 @@ import (
 // conversion deadline.
 //
 // Echo cancels the request context as soon as the synchronous handler returns
-// [api.ErrAsyncProcess], which would abort the asynchronous work. Replacing the
-// embedded context severs that cancellation. The returned cancel function
-// cleans up both the detached context and the original working directory.
+// [api.ErrAsyncProcess], which would abort the asynchronous work. Detaching via
+// [context.WithoutCancel] severs that cancellation while keeping the context
+// values, most importantly the active trace span, so downstream conversion and
+// webhook spans stay in the caller's trace instead of starting a new one.
+// [context.WithoutCancel] also drops the deadline, so it is re-layered. The
+// returned cancel function cleans up both the detached context and the original
+// working directory.
 func detachAsyncContext(ctx *api.Context, cancel context.CancelFunc) context.CancelFunc {
-	if deadline, ok := ctx.Deadline(); ok {
-		detachedCtx, detachedCancel := context.WithDeadline(context.Background(), deadline)
-		ctx.Context = detachedCtx
+	deadline, hasDeadline := ctx.Deadline()
+	base := context.WithoutCancel(ctx.Context)
 
-		originalCancel := cancel
-		return func() {
-			detachedCancel()
-			originalCancel()
-		}
+	var detachedCtx context.Context
+	var detachedCancel context.CancelFunc
+	if hasDeadline {
+		detachedCtx, detachedCancel = context.WithDeadline(base, deadline)
+	} else {
+		// Fallback if no deadline was set (rare, as newContext enforces it).
+		detachedCtx, detachedCancel = context.WithCancel(base)
 	}
+	ctx.Context = detachedCtx
 
-	// Fallback if no deadline was set (rare, as newContext enforces it).
-	ctx.Context = context.Background()
-	return cancel
+	originalCancel := cancel
+	return func() {
+		detachedCancel()
+		originalCancel()
+	}
 }

pkg/modules/webhook/async_context_test.go

@@ -5,9 +5,37 @@ import (
 	"testing"
 	"time"
 
+	"go.opentelemetry.io/otel/trace"
+
 	"github.com/gotenberg/gotenberg/v8/pkg/modules/api"
 )
 
+func TestDetachAsyncContext_PreservesTraceContext(t *testing.T) {
+	traceID, _ := trace.TraceIDFromHex("0123456789abcdef0123456789abcdef")
+	spanID, _ := trace.SpanIDFromHex("0123456789abcdef")
+	sc := trace.NewSpanContext(trace.SpanContextConfig{
+		TraceID:    traceID,
+		SpanID:     spanID,
+		TraceFlags: trace.FlagsSampled,
+		Remote:     true,
+	})
+
+	reqCtx, reqCancel := context.WithDeadline(
+		trace.ContextWithSpanContext(context.Background(), sc),
+		time.Now().Add(2*time.Hour),
+	)
+	defer reqCancel()
+
+	ctx := &api.Context{Context: reqCtx}
+	cancel := detachAsyncContext(ctx, func() {})
+	defer cancel()
+
+	got := trace.SpanContextFromContext(ctx.Context)
+	if got.TraceID() != sc.TraceID() {
+		t.Errorf("expected the detached context to keep trace id %s, got %s", sc.TraceID(), got.TraceID())
+	}
+}
+
 func TestDetachAsyncContext_PreservesDeadline(t *testing.T) {
 	deadline := time.Now().Add(2 * time.Hour)
 	reqCtx, reqCancel := context.WithDeadline(context.Background(), deadline)