Gauge metrics do not expose `sum` in the UI

[haoyi-amilabs]

Environment

SaaS (https://sentry.io/)

Steps to Reproduce

The official website says

I'd like to be able to generate a chart of all the gauges across the group_by categories summed together. Ideally with things like stacked charts and stuff, but even a single line would be fine too

Expected Result

Gauges let you obtain aggregates like min, max, avg, sum, and count. They can be represented in a more space-efficient way than distributions, but they can't be used to get percentiles. If percentiles aren't important to you, we recommend using gauges.

Actual Result

But when I try to create a chart, there is no sum:

Product Area

Dashboards

Link

No response

DSN

No response

Version

No response

[linear-code]

ENG-8395

[getsantry]

Assigning to @getsentry/support for routing ⏲️

[haoyi-amilabs]

Codex says

sum is a generic trace-metric aggregate
whose accepted metric-type literal explicitly includes gauge. That support was added when
trace-metric aggregates were introduced. The frontend’s gauge option list omitted sum from
its first commit.

• Backend computation: implemented.
• Current Application Metrics UI: never exposed.
• Documentation/product contract: declares it unsupported.
• New trace-metrics end-to-end coverage for sum(..., gauge, ...): absent.

Of course, the public docs do declare it supported as linked in the original isseu