fix(llmobs): llmobs data can be sent to agent proxy running on uds

[sabrenner]

What does this PR do?

Fixes an issue where LLMObs data could not be sent to an agent proxy running on a unix domain socket. This is accomplished by passing the base URL and path separately into the request, instead of constructing the URL dynamically.

The only other change is aesthetic for logging - making sure the URL string is properly formatted for logging configuration for llmobs, and for when data is sent.

Testing

Aside from some unit tests written and modified for this change, I tested locally using the setup described via our corp docs
with a dummy app that creates 1 span and 1 evaluation metric.

Configuring LLMObsEvalMetricsWriter to unix:///var/run/datadog/apm.socket/evp_proxy/v2/api/intake/llm-obs/v1/eval-metric
Configuring LLMObsSpanWriter to unix:///var/run/datadog/apm.socket/evp_proxy/v2/api/v2/llmobs

...

Sent 1 LLMObs evaluation_metric events to unix:///var/run/datadog/apm.socket/evp_proxy/v2/api/intake/llm-obs/v1/eval-metric
Sent 1 LLMObs span events to unix:///var/run/datadog/apm.socket/evp_proxy/v2/api/v2/llmobs

and indeed the span shows up in the UI:

Motivation

MLOB-2736

[github-actions]

Overall package size

Self size: 9.3 MB
Deduped: 102.55 MB
No deduping: 103.07 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | @datadog/libdatadog | 0.5.1 | 29.73 MB | 29.73 MB | | @datadog/native-appsec | 8.5.2 | 19.33 MB | 19.34 MB | | @datadog/native-iast-taint-tracking | 3.3.1 | 13.99 MB | 13.99 MB | | @datadog/pprof | 5.7.1 | 9.51 MB | 9.88 MB | | @opentelemetry/core | 1.30.1 | 908.66 kB | 7.16 MB | | protobufjs | 7.4.0 | 2.77 MB | 5.42 MB | | @datadog/wasm-js-rewriter | 4.0.1 | 2.85 MB | 3.58 MB | | @datadog/native-metrics | 3.1.1 | 1.02 MB | 1.43 MB | | @opentelemetry/api | 1.8.0 | 1.21 MB | 1.21 MB | | import-in-the-middle | 1.13.1 | 117.64 kB | 839.26 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 | 2.1.1 | 109.9 kB | 109.9 kB | | lodash.sortby | 4.7.0 | 75.76 kB | 75.76 kB | | ignore | 5.3.2 | 53.63 kB | 53.63 kB | | istanbul-lib-coverage | 3.2.0 | 29.34 kB | 29.34 kB | | rfdc | 1.4.1 | 27.15 kB | 27.15 kB | | @isaacs/ttlcache | 1.4.1 | 25.2 kB | 25.2 kB | | dc-polyfill | 0.1.8 | 25.08 kB | 25.08 kB | | tlhunter-sorted-set | 0.1.0 | 24.94 kB | 24.94 kB | | shell-quote | 1.8.2 | 23.54 kB | 23.54 kB | | limiter | 1.1.5 | 23.17 kB | 23.17 kB | | retry | 0.13.1 | 18.85 kB | 18.85 kB | | semifies | 1.0.0 | 15.84 kB | 15.84 kB | | jest-docblock | 29.7.0 | 8.99 kB | 12.76 kB | | crypto-randomuuid | 1.0.0 | 11.18 kB | 11.18 kB | | ttl-set | 1.0.0 | 4.61 kB | 9.69 kB | | mutexify | 1.4.0 | 5.71 kB | 8.74 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}

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.10%. Comparing base (9721d08) to head (aa445ab).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/dd-trace/src/llmobs/writers/base.js	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5679      +/-   ##
==========================================
- Coverage   79.13%   79.10%   -0.03%     
==========================================
  Files         513      513              
  Lines       23500    23511      +11     
==========================================
+ Hits        18596    18599       +3     
- Misses       4904     4912       +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-07 17:23:28

Comparing candidate commit aa445ab in PR branch sabrenner/fix-llmobs-writers-for-unix-socket with baseline commit 9721d08 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1271 metrics, 52 unstable metrics.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: sabrenner/fix-llmobs-writers-for-unix-socket
Commit report: a17dab0
Test service: dd-trace-js-integration-tests

✅ 0 Failed, 935 Passed, 0 Skipped, 15m 41.84s Total Time