[MLOB-1981] fix(llmobs): childOf applies to LLM Observability spans

[sabrenner]

What does this PR do?

Has the LLMObs SDK respect the childOf option when instrumenting spans with LLM Observability. If childOf is specified, we will activate the function in the context of that span if it is an LLM Observability span, otherwise activate it in the scope of the current active LLMObs span.

This is useful for cases where you might want to have a callback run in the same scope as the function that invoked it:

let llmSpan

function myLlm () {
  setTimeout(myTask, 200)
  llmobs.trace({ ... }, span => { 
    llmSpan = span 
    // some other task that keeps this span alive for more than 200ms
  })
}

function myTask () {
  llmobs.trace({ ..., childOf: llmSpan }, () => ...)
}

as we do not have a way of currently activating myTask in the scope of the traced function, since the function is not called before the scope of the llmobs.trace in myLlm closes. Respecting the childOf argument helps with this.

Motivation

Fixes parentage in cases of manual instrumentation.

[github-actions]

Overall package size

Self size: 8.24 MB
Deduped: 94.81 MB
No deduping: 95.37 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | @datadog/libdatadog | 0.2.2 | 29.27 MB | 29.27 MB | | @datadog/native-appsec | 8.3.0 | 19.37 MB | 19.38 MB | | @datadog/native-iast-taint-tracking | 3.2.0 | 13.9 MB | 13.91 MB | | @datadog/pprof | 5.4.1 | 9.76 MB | 10.13 MB | | protobufjs | 7.2.5 | 2.77 MB | 5.16 MB | | @datadog/native-iast-rewriter | 2.6.0 | 2.58 MB | 2.72 MB | | @opentelemetry/core | 1.14.0 | 872.87 kB | 1.47 MB | | @datadog/native-metrics | 3.0.1 | 1.06 MB | 1.46 MB | | @opentelemetry/api | 1.8.0 | 1.21 MB | 1.21 MB | | import-in-the-middle | 1.11.2 | 112.74 kB | 826.22 kB | | msgpack-lite | 0.1.26 | 201.16 kB | 281.59 kB | | source-map | 0.7.4 | 226 kB | 226 kB | | opentracing | 0.14.7 | 194.81 kB | 194.81 kB | | lru-cache | 7.18.3 | 133.92 kB | 133.92 kB | | pprof-format | 2.1.0 | 111.69 kB | 111.69 kB | | @datadog/sketches-js | 2.1.0 | 109.9 kB | 109.9 kB | | semver | 7.6.3 | 95.82 kB | 95.82 kB | | lodash.sortby | 4.7.0 | 75.76 kB | 75.76 kB | | ignore | 5.3.1 | 51.46 kB | 51.46 kB | | int64-buffer | 0.1.10 | 49.18 kB | 49.18 kB | | shell-quote | 1.8.1 | 44.96 kB | 44.96 kB | | istanbul-lib-coverage | 3.2.0 | 29.34 kB | 29.34 kB | | rfdc | 1.3.1 | 25.21 kB | 25.21 kB | | @isaacs/ttlcache | 1.4.1 | 25.2 kB | 25.2 kB | | tlhunter-sorted-set | 0.1.0 | 24.94 kB | 24.94 kB | | limiter | 1.1.5 | 23.17 kB | 23.17 kB | | dc-polyfill | 0.1.4 | 23.1 kB | 23.1 kB | | retry | 0.13.1 | 18.85 kB | 18.85 kB | | jest-docblock | 29.7.0 | 8.99 kB | 12.76 kB | | crypto-randomuuid | 1.0.0 | 11.18 kB | 11.18 kB | | path-to-regexp | 0.1.12 | 6.6 kB | 6.6 kB | | koalas | 1.0.2 | 6.47 kB | 6.47 kB | | module-details-from-path | 1.0.3 | 4.47 kB | 4.47 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[Yun-Kim]

small question but otherwise lgtm. thanks!

[Yun-Kim]

if childOf is null (example: the queued task does not end up executing), do we handle this case here?

[Kyle-Verhoog]

one small thought about the handling of unexpected values, otherwise good to me!

[Kyle-Verhoog]

I think this condition would subtly hide programming errors with the type of childOf. I'd rather we just take the value of childOf if specified and let it fail wherever it might if it's the wrong type or fail hard up front in these cases rather than subtly falling back to parent here.