feat(llmobs): propagate mlApp for LLM proxy or gateway services

[sabrenner]

What does this PR do?

Adds mlApp propagation for use cases with a proxy service that might expect to receive requests from many different mlApps. This enables easier enablement in services using LLM Observability that aren't mlApp-specific.

Motivation

Easier onboarding and observability experience for LLM proxy/gateway services.

[codecov]

Codecov Report

Attention: Patch coverage is 58.33333% with 5 lines in your changes missing coverage. Please review.

Project coverage is 78.99%. Comparing base (0672b4d) to head (bb7e092).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/dd-trace/src/llmobs/index.js	42.85%	4 Missing ⚠️
packages/dd-trace/src/llmobs/tagger.js	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5553      +/-   ##
==========================================
- Coverage   79.04%   78.99%   -0.06%     
==========================================
  Files         515      512       -3     
  Lines       23589    23482     -107     
==========================================
- Hits        18647    18550      -97     
+ Misses       4942     4932      -10     

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-19 17:23:11

Comparing candidate commit bb7e092 in PR branch sabrenner/ml-app-propagation with baseline commit 0672b4d in branch master.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 1269 metrics, 53 unstable metrics.

scenario:plugin-bluebird-control-22

• 🟥 cpu_user_time [+6.503ms; +10.297ms] or [+5.800%; +9.184%]

[github-actions]

Overall package size

Self size: 9.39 MB
Deduped: 103.41 MB
No deduping: 103.93 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/pprof | 5.8.0 | 12.55 MB | 12.92 MB | | @datadog/native-iast-taint-tracking | 4.0.0 | 11.72 MB | 11.73 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}

[datadog-datadog-prod-us1]

Datadog Report

Branch report: sabrenner/ml-app-propagation
Commit report: df4e938
Test service: dd-trace-js-integration-tests

✅ 0 Failed, 985 Passed, 0 Skipped, 14m 43.86s Total Time