Detect request coalescing?

[Batanun B]

Just a quick question that I wasn't able to find any information on using regular google searches. Is it possible to detect request coalescing somehow? Meaning that, when looking at the response headers, can I somehow see that the request had to wait for another request for the same resource to finish, before this request could return? Can I somehow detect that in VCL, and add a custom header with that information?

Regards
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