chore(llmobs): remove beta auto span linking flag, decorator linking

[Yun-Kim]

This PR removes the _DD_LLMOBS_AUTO_SPAN_LINKING_ENABLED configuration flag. This is a beta feature that was previously private, but no longer disabled by default. However removing this flag is not a breaking change, as this will simply add functionality (add span linking in our integrations and decorators).

This PR also removes the auto span linking feature for decorator spans. This was an experimental feature that we started when we first introduced span linking, but we've decided to remove this for now and keep span linking limited to our integrations.

In hindsight it should be noted that adding this option to the config.py file was probably a mistake, since it was a private feature flag that was destined to be removed fairly soon. We should have just read it directly as an environment variable, but wanted to reiterate that removing this from the config.py file is not a breaking change (although it would be normally) since this is a private feature flag for experimental users.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/llmobs/_integrations/base.py                                    @DataDog/ml-observability
ddtrace/llmobs/_integrations/langchain.py                               @DataDog/ml-observability
ddtrace/llmobs/decorators.py                                            @DataDog/ml-observability
ddtrace/settings/_config.py                                             @DataDog/apm-core-python
tests/llmobs/_utils.py                                                  @DataDog/ml-observability
tests/llmobs/test_llmobs_decorators.py                                  @DataDog/ml-observability
tests/telemetry/test_writer.py                                          @DataDog/apm-python
tests/utils.py                                                          @DataDog/python-guild

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 238 ± 5 ms.

The average import time from base is: 238 ± 4 ms.

The import time difference between this PR and base is: -0.4 ± 0.2 ms.

The difference is not statistically significant (z = -1.89).

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 1.879 ms (0.79%)

ddtrace.bootstrap.sitecustomize 1.219 ms (0.51%)

ddtrace.bootstrap.preload 1.219 ms (0.51%)

ddtrace.internal.products 1.219 ms (0.51%)

ddtrace.internal.remoteconfig.client 0.599 ms (0.25%)

ddtrace 0.660 ms (0.28%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-04-07 18:54:39

Comparing candidate commit 291112d in PR branch yunkim/llmobs-enable-span-linking with baseline commit 612d802 in branch main.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 495 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathsplit_aspect

• 🟥 execution_time [+449.754ns; +512.441ns] or [+11.590%; +13.205%]

[christophe-papazian]

Approved, but some llmobs snapshot tests are failing, (maybe?) due to the span_links tag