feat: OTel context sharing

[morrisonlevi]

Description

This adds OTel context sharing using libdatadog. It adds it to both tracing (producer) and profiling (consumer).

This is mostly AI-written with a little human review as I went. It is not ready for merge, but it did pass some local end-to-end experimentation.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-datadog-prod-us1]

 

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⚠️ Warnings

🚦 42 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-php | ASAN test_c with multiple observers: [8.5]     

DataDog/apm-reliability/dd-trace-php | compile extension windows: [7.2]     

DataDog/apm-reliability/dd-trace-php | compile extension windows: [7.3]     

View all 42 failed jobs.

ℹ️ Info

No other issues found (see more)

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 54.11% (+0.00%)

Useful? React with 👍 / 👎

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🔗 Commit SHA: a449010 | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks [ profiler ]

Benchmark execution time: 2026-06-15 21:04:55

Comparing candidate commit a449010 in PR branch levi/otel-thread-context with baseline commit 1d6b7ca in branch master.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 26 metrics, 8 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:php-profiler-timeline-memory-control

• 🟥 cpu_user_time [+31.216ms; +36.582ms] or [+5.183%; +6.074%]
• 🟥 execution_time [+32.141ms; +36.915ms] or [+5.108%; +5.867%]

[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-06-15 22:05:54

Comparing candidate commit a449010 in PR branch levi/otel-thread-context with baseline commit 1d6b7ca in branch master.

Found 1 performance improvements and 3 performance regressions! Performance is the same for 190 metrics, 0 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:MessagePackSerializationBench/benchMessagePackSerialization-opcache

• 🟩 execution_time [-4.916µs; -2.944µs] or [-4.333%; -2.595%]

scenario:PDOBench/benchPDOOverhead

• 🟥 execution_time [+9.550µs; +11.833µs] or [+3.750%; +4.647%]

scenario:PDOBench/benchPDOOverheadWithDBM

• 🟥 execution_time [+9.456µs; +12.357µs] or [+3.703%; +4.839%]

scenario:PHPRedisBench/benchRedisOverhead

• 🟥 execution_time [+53.107µs; +70.110µs] or [+5.279%; +6.969%]