refactor(webhook): extract async context detach into a helper

pkg/modules/webhook/async_context.go

@@ -0,0 +1,32 @@
+package webhook
+
+import (
+	"context"
+
+	"github.com/gotenberg/gotenberg/v8/pkg/modules/api"
+)
+
+// detachAsyncContext detaches ctx from the inbound request lifecycle so the
+// webhook goroutine survives echo recycling the request, while preserving the
+// 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.
+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
+
+		originalCancel := cancel
+		return func() {
+			detachedCancel()
+			originalCancel()
+		}
+	}
+
+	// Fallback if no deadline was set (rare, as newContext enforces it).
+	ctx.Context = context.Background()
+	return cancel
+}