Misleading TTFB when using 103 early hints

It seems that when enabling 103 early hints the TTFB is misleading (entry.responseStart) on the main page as it is not the response for this very request but rather for the resource that was pushed

How can we measure the time to the first byte of payload data?

FWIW, there’s quite a bit of discussion in the specs spaces about how early hints should be exposed. As things currently stand, early hints “count” as the start of the response but it’s clear that they should probably be separated out into several different metrics:

  • Time to first headers
  • Time to final headers
  • Time to first payload bytes

Probably best for @tkadlec and crew to weigh in on the desired end state for WPT because it’s easy enough to implement the technical changes in the agent.