fix: improve baggage implementation

[BridgeAR]

This addresses multiple baggage issues and adds further documentation to the new implementation.
The regular API is now spec compliant by ignoring non string keys as well as returning the new context consistently when needed.

Baggage headers are also improved by not accepting arbitrary strings as keys anymore. They now adhere to the spec as outlined in the code comment.
In addition, the parsing now handles optional properties that may be attached.

TODO:
This is lacking additional tests for the improvements. Especially system tests should be used for the headers.

[github-actions]

Overall package size

Self size: 4.41 MB
Deduped: 5.24 MB
No deduping: 5.24 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 2.0.0 | 68.46 kB | 797.03 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB |

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.37%. Comparing base (971bdd5) to head (398f1e0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7279      +/-   ##
==========================================
+ Coverage   85.14%   85.37%   +0.23%     
==========================================
  Files         532      316     -216     
  Lines       22897    12204   -10693     
==========================================
- Hits        19495    10419    -9076     
+ Misses       3402     1785    -1617     

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[datadog-official]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 3 Tests failed

esbuild 0.27.0 "before all" hook for "works" from esbuild 0.27.0 (Datadog) (Fix with Cursor)

spawnSync /bin/sh ETIMEDOUT

Error: spawnSync /bin/sh ETIMEDOUT
    at Object.spawnSync (node:internal/child_process:1120:20)
    at spawnSync (node:child_process:902:24)
    at Object.execSync (node:child_process:983:15)
    at execSync (integration-tests/esbuild/index.spec.js:18:10)
    at Context.<anonymous> (integration-tests/esbuild/index.spec.js:37:7)
    at process.processImmediate (node:internal/timers:485:21)

esbuild 0.16.12 "after all" hook for "prints a warning when user opts to minify output without retaining class names" from ESM (Datadog) (Fix with Cursor)

spawnSync /bin/sh ETIMEDOUT

Error: spawnSync /bin/sh ETIMEDOUT
    at Object.spawnSync (node:internal/child_process:1117:20)
    at spawnSync (node:child_process:876:24)
    at Object.execSync (node:child_process:957:15)
    at execSync (integration-tests/esbuild/index.spec.js:18:10)
    at Context.<anonymous> (integration-tests/esbuild/index.spec.js:47:7)
    at process.processImmediate (node:internal/timers:476:21)

tests.parametric.test_headers_baggage.Test_Headers_Baggage_Span_Tags.test_baggage_span_tags_malformed_header[parametric-nodejs] from system_tests_suite (Datadog) (Fix with Cursor)

AssertionError: assert '' is None
 +  where '' = <built-in method get of dict object at 0x7f236352abc0>('baggage.user.id')
 +    where <built-in method get of dict object at 0x7f236352abc0> = {'_dd.integration': 'opentracing', '_dd.p.dm': '-0', '_dd.rc.client_id': 'f626f603-1dd2-450c-b2b1-b6711e432f82', 'baggage.account.id': 'abcd', ...}.get

self = <tests.parametric.test_headers_baggage.Test_Headers_Baggage_Span_Tags object at 0x7f2395a56480>
test_agent = <utils.docker_fixtures._test_agent.TestAgentAPI object at 0x7f2360f08fb0>
test_library = <utils.docker_fixtures._test_clients._test_client_parametric.ParametricTestClientApi object at 0x7f23610ff9b0>

    def test_baggage_span_tags_malformed_header(self, test_agent: TestAgentAPI, test_library: APMLibrary) -> None:
        with test_library:
...

ℹ️ Info

❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 398f1e0 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-01-20 02:16:09

Comparing candidate commit 398f1e0 in PR branch BridgeAR/2026-01-19-improve-baggage with baseline commit 971bdd5 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 230 metrics, 30 unstable metrics.