CHW-4824 IdempotencyKeyConflict

Idempotency-Key was reused with a different request body; pick a fresh key or resend the original body to receive the cached response

Default message: Idempotency-Key was reused with a different request body; pick a fresh key or resend the original body to receive the cached response
HTTP status: 409 (client)

Problem. An idempotent request was rejected because the Idempotency-Key header matches a stored response that was generated for a different request body. Cause. The caller is reusing a key across distinct operations. Fix. Pick a fresh key, or send the original body to receive the cached reply. HTTP 409.