I hadn't considered dynamic urls as the dominant use case. But I can certainly see the importance in handling them as well. To me that feel like a function memo

I hadn't considered dynamic urls as the dominant use case. But I can certainly see the importance in handling them as well. To me that feel like a function memoization problem (e.g. this example was a function of 2 parameters, height and width). For that case passing along cache-control: immutable, integrity: sha-abc123 headers in the response feels like the best current solution. Though it would be nice to somehow have the url self-descriptively assert its purity. Something to the effect of saying `I don't have the content-hash for this now but whatever i return is going to be immutable`, rather than having to muck around in the web-server protocol layer to assert that fact via cache-control: immutable. I think fundamentally the metadata on whether a particular url is immutable/pure or not, should be self evident, rather than buried in as an implementation detail in the response's http header.