Synchronous validation on async path

Heavy synchronous checks run in an async/event loop, blocking responsiveness.

Stream/validate incrementally; offload to worker threads/background jobs; pre-validate at edges; benchmark and set budgets

Observable signs that may indicate Synchronous validation on async path:

• UI stutters during parsing/validation on input.
• Server event loop stalls when validating large payloads.
• Throughput collapses under heavy synchronous checks.